A review of cell/organ biology

Chapter 3 – Macromolecules and the Origin of Life

3.1 What Kinds of Molecules Characterize Living Things?

-Molecules in living organisms: proteins, carbohydrates, lipids, nucleic acids

-Polymers are made of smaller monomers

-Macromolecules: polymers with molecular weights >1000

Functional groups give specific properties to molecules

-Functional groups: groups of atoms with specific chemical properties and consistent behavior; confers these properties when attached to large molecules

Isomers have different arrangements of the same atoms

-Isomers: molecules with the same chemical formula, but atoms are arranged differently

            -Structural isomer: differ in how their atoms are joined together

The structures of macromolecules reflect their functions

-Biochemical unity: organisms obtain required macromolecules by eating other organisms

-One macromolecule can contain many different functional groups – determines shape and function

Most macromolecules are formed by condensation and broken down by hydrolysis

-Condensation reaction: polymers are formed; monomers joined by covalent bonds and a water is removed, also called dehydration reaction

-Hydrolysis: polymers are broken down into monomers in hydrolysis

3.2 What Are the Chemical Structures and Functions of Proteins?

-Functions of proteins: structural support, protection, transport, catalysis, defense, regulation, movement

Amino acids are the building blocks of proteins

            -Proteins are made from 20 different amino acids

            -Amino acids are distinguished by their side chains

                        -3 have + charged hydrophilic side chains

                        -2 have – charged hydrophilic side chains

                        -5 have polar but neutral hydrophilic side chains

                        -7 have nonpolar hydrophobic side chains

-3 are special cases, generally hydrophobic (cysteine forms disulfide bridge, glycine’s side chain is single H atom and can fit into tight corners in the interior of protein, proline posses modified amino group lacking a H on its N, limits H-bonding ability, ring structure limits rotation about α carbon, so found at bends/loops of protein)

Peptide bonds form the backbone of a protein

-Amino acids bond together covalently by peptide bonds to form polypeptide chain

-First: amino group of first amino acid – N terminus

-Last: carboxyl group of last amino acid – C terminus

The primary structure of a protein is its amino acid sequence

            -Sequence determines secondary and tertiary structure

The secondary structure of a protein requires hydrogen bonding

            -α helix: right-handed coil, R groups extend outward from peptide backbone

-β pleated sheet: two or more polypoptide chains that are almost completely extended aligned, stabilized by H-bonds between NH on one chain and C=O on the other

The tertiary structure of a protein is formed by bending and folding

            -Bending and folding of α helix/β pleated sheet forms 3-D shape

            -Outer surfaces present functional groups that can interact with other molecules

The quaternary structure of a protein consists of subunits

-Results from interaction of subunits by hydrophobic interactions, van der Waals, ionic bonds, & H-bonds

Both shape and surface chemistry contribute to protein specificity

-Specific shape and functional groups determines function & allows it to bind non-covalently with another molecule - ligand

3.3 What Are the Chemical Structures and Functions of Carbohydrates?

            -Carbohydrates: carbon is flanked by hydrogen & hydroxyl groups

-carbon skeleton for many other molecules

-Monosaccharide: simple sugar, pentoses, hexoses, simplest sugar has 3 carbons (glyceraldehyde)

-Disaccharide: 2 simple sugars linked by covalent bonds

-Oligosaccharide: 3-20 monosaccharides

-Polysaccharides: 100’s to 1000’s of monosaccharides: starch, glycogen, cellulose

Monosaccharides are simple sugars

            -All living cells use glucose, which exists as chain or ring form (more stable)

Glycosidic linkages bond monosaccharides

            -single glycosidic linkage forms disaccharide from two monosaccharides

-oligosaccharides may include other functionjal groups, often covalently bonded to proteins/lipids on cell surfaces, act as recognition signals

Polysaccharides store energy and provide structural materials

            -Starch: storage of glucose in plants (slightly branched)

            -Glycogen: storage of glucose in animals (highly branched)

            -Cellulose: stable, good structural component (linear)

Chemically modified carbohydrates contain additional functional groups

            -Sugar phosphates: important intermediates in cellular energy reactions

            -Amino sugars: important in extracellular matrix

3.4 What Are the Chemical Structures and Functions of Lipids?

            -Fats and oils store energy

            -Phospholipids play important structural roles in cell membranes

            -Carotenoids help plants capture light energy

            -Steroids/modified fatty acids play regulatory roles as hormones & vitamins

            -Fats in animal bodies = thermal insulation

            -Lipid coating around nerves = electrical insulation

            -Oil/wax on surfaces of skin/fur/feathers repels water

Fats and oils store energy

            -Fats & oils are triglycerides – made of 3 fatty acids + 1 glycerol (ester linkage)

            -Saturated fatty acids: saturated with hydrogen atoms

-Unsaturated fatty acids: some double bonds in carbon chain (can be mono or poly unsaturated)

-Animal fats: saturated; plant oils: unsaturated

Phospholipids form biological membranes

            -One fatty acid group is replaced by phosphate in triglyceride

            -Phosphate head = hydrophilic, fatty acid tails = hydrophobic

            -Forms bilayer: hydrophilic heads outside, hydrophobic tails inside

Not all lipids are triglycerides

            -Steroids: multiple rings share carbons (6, 6, 6, 5)

3.5 What Are the Chemical Structures and Functions of Nucleic Acids?

            -DNA (deoxyribonucleic acid) & RNA (Ribonucleic acid)

Nucleotides are the building blocks of nucleic acids

            -Nucleotides consist of pentose sugar, phosphate group, & nitrogen-containing base

            -Pyrimidine (single ring base), Purine (fused ring structure)

            -Pentose sugar + nitrogenous base (but no phosphate) = nucleoside

The uniqueness of a nucleic acid resides in its nucleotide sequence

            -DNA bases: Adenine (A), Cytosine (C), Guanine (G), Thymine (T)

            -Complementary base pairing: A-T, C-G (Purine with Pyrimidine)

            -DNA is purely informational molecule

            -RNA uses information to determine the sequence of amino acids in proteins

            -2 strands of DNA molecule forms double helix

            -DNA carries hereditary information between generations

            -Determining sequence of bases helps reveal evolutionary relationships

            -Closest living relative of human is the chimpanzee

-Central dogma of molecular biology: DNA in the genome is transcribed into RNA which is translated into protein

Chapter 4 – Cells: Working Units of Life

4.1 What Features of Cells Make Them the Fundamental Unit of Life?

-Light microscopes: glass lense to focus visible light, resolution of 0.2 μm

-Electron microscopes: electromagnets to focus electron beam, resolution of 0.5 nm

-Limit of Resolution = 0.61 x wavelength/NA

Cells are surrounded by a plasma membrane

-Plasma membrane: continuous membrane composed of lipid bilayer with proteins floating within

            -Fluid Mosaic model by Nicholson & Singer

            -Roles of the plasma membrane

                        -Act as selectively permeable barrier

-Interface for cells where information is received from adjacent cells and extracellular signals

                        -Allow cells to maintain a constant internal environment

                        -Has molecules that are responsible for binding and adhering to adjacent cells

Cells are prokaryotic or eukaryotic

            -Prokaryotes: no nucleus or other membrane-enclosed compartments. Lack distinct organelles

-Eukaryotes: membrane-enclosed nucleus and other membrane-enclosed compartments (organelles)

4.2 What Are the Characteristics of Prokaryotic Cells?

Prokaryotic cells share certain features

            -Plasma membrane: encloses cell, regulates traffic, separate cell from environment

            -Nucleoid: contains hereditary material (DNA) of cell

            -Cytosol: water, dissolved ions, small molecules, soluble macromolecules (proteins)

            -Ribosomes: complexes of RNA, sites of protein synthesis

Some prokaryotic cells have specialized features

-Cell walls: made of peptidoglycan for most bacteria; some bacteria has outer membrane (polysaccharide-rich phospholipid membrane); others have capsule, but can survive without

-Internal membranes: some bacteria, including cyanobacteria, can carry on photosynthesis; plasma membrane is infolded and has chlorophyll

-Flagella and pili: flagella is locomotory structure shaped like corkscrew; pili are threadlike structures that help bacteria adhere to one another during mating or to other cells for food & protection

4.3 What Are the Characteristics of Eukaryotic Cells?

            -Eukaryotes have membrane-enclosed nucleus in each cell, and:

                        -tend to be larger than prokaryotic cells

                        -has variety of membrane-enclosed compartments called organelles

                        -has protein scaffolding called the cytoskeleton

Compartmentalization is the key to eukaryotic cell function

            -each organelle/compartment has specific role defined by chemical process

-membranes surrounding organelles keep away inappropriate molecule; act as traffic regulators for raw materials in/out of the organelle

Some organelles process information

            -Nucleus: largest organelle in cell, approx 5 μm in diameter

                        -site of DNA replication, genetic control of cell’s activities

                        -nucleolus assembles ribosomes

                        -two lipid bilayers form the nuclear envelope, perforated with nuclear pores

                        -nuclear pores connect interior of nucleus with rest of cytoplasm

                        -pore complex, consisting of 8 large protein granules, surrounds each pore

                        -RNA & proteins must pass through these pores to enter or leave nucleus

-chromatin consists of diffuse/very long, thin fibers in which DNA is bound to proteins

                        -these condense and organize into chromosomes prior to cell division

                        -nucleoplasm surrounds chromatin

-nuclear lamina is meshwork of proteins which maintains the shape of the nuclear envelope and the nucleus

            -Ribosomes: sites of protein synthesis

-functional ribosomes found free in cytoplasm, in mitochondria, bound to endoplasmic reticulum, and in chloroplasts

                        -consist of a type of RNA called rRNA & more than 50 other proteins

The endomembrane system is a group of interrelated organelles

-Cells specialized for synthesizing proteins for extracellular transport have extensive ER membrane systems

            -Rough endoplasmic reticulum: has ribosomes attached

-segregate newly synthesized proteins away from cytoplasm, transports them to other locations in the cell

-proteins can be chemically modified in RER to alter function & eventual destination

            -Smooth endoplasmic reticulum: ribosome-free area of ER

                        -chemically modifies small molecules taken in by cell: drugs & pesticides

                        -site for hydrolysis of glycogen in animal cells

                        -site of synthesis of lipids & steroids

-Golgi apparatus: consists of flattened membranous sacs (called cisternae) & small membrane-enclosed vesicles

                        -receives proteins from ER, may further modify them

                        -concentrate, package, & sort proteins before sent to destination

                        -some polysaccharides for plant cell walls synthesized

                        -come in on cis side, lave on trans side, cisternae in middle = medial region

            -Lysosomes: vesicles containing digestive enzymes that come in part from the Golgi

                        -sites for breakdown of food/foreign material brought into cell by phagocytosis

                        -sites where digestion of spent cellular components occurs (autophagy)

Some organelles transform energy

            -Mitochondria: convert potential chemical energy of fuel into form cells can use (ATP)

                        -production of ATP is called cellular respiration

                        -mitochondria have an outer lipid bilayer & highly folded inner membrane

-folds of inner membrane = cristae, contains large protein molecules used in cellular respiration

-region enclosed by inner membrane = mitochondrial matrix, where citric acid cycle takes place

            -Plastids: organelles found only in plants & some protists

            -Chloroplasts: one type of plastid, site where photosynthesis occurs

                        -Surrounded by two layers, have internal membrane system

-Inner membranes arranged as thylakoids (stacks of thylakoid are grana), contain chlorophyll & other pigments

                        -Fluid in which grana are suspended = stroma

Several other organelles are surrounded by a membrane

-Peroxisomes: aka microbodies; small organelles specialized to compartmentalize toxic peroxides & break them down into H₂O and O₂; catalyzed by catalase

-Glyoxysome: structurally similar to peroxisomes; found in plants; store lipids are converted into carbohydrates

The cytoskeleton is important in cell structure:

            -Maintains cell shape & support

            -Provides mechanisms for cell movement

            -Act as tracks for motor proteins that help move material within cells

            -Three major types of cytoskeletal components: MF, IF, MT

            -Microfilaments: made of actin, exist as single filament, bundles, or networks

-needed for cell contraction (muscle), add structure to plasma membrane & shape to cells

                        -involved in cytoplasmic streaming, formation of pseudopodia

-Intermediate filaments: found only in multicellular organisms; forms ropelike assemblage

                        -2 structural functions: stabilize cell structure, resist tension

                        -in some cells, maintain position of nucleus & other organelles

-amino acid sequence in heptad (a, d, hydrophobic), α helix has hydrophobic stripe down the length, and two subunits wrap around each other

            -Microtubules: hollow cylinders made from tubulin protein subunits

                        -provide rigid intracellular skeleton

                        -function as tracks that motor proteins can move along in cell

                        -regularly form and disassemble as needs of cell change

                        -in animal cells, centrioles are aggregates of microtubules

-capped by GTP; formation of GTP cap stabilizies microtubule & causes it to grow at + end; if GTP cap is lost, microtubule quickly disassembles

            -Cilia/Flagella: common locomotion appendages, made of microtubules

                        -Flagella: typically longer than cilia, cells only have one or two

                        -Cilia: are shorter, present in great numbers

-microtubules in cilia/flagella arranged in 9+2 array; at base of each is a basal body; 9 pairs extend into basal body

-centrioles are similar to basal bodies, but located at center of cell & help in movement of chromosomes during cell division

            -Motor proteins: move along microtubules

                        -in both cilia/flagella, microtubules cross-linked by spokes of dynein

                        -dynein changes shape when energy is released from ATP

                        -many dynein molecules associate along length of microtubule pair

                        -dynein moves toward – end, kinesin moves to + end

4.4 What Are the Roles of Extracellular Structures?

-Multicellular animals have an extracellular matrix composed of fibrous proteins, such as collagen  and glycoproteins

-Functions of the extracellular matrix

            -Hold cells together in tissues

            -Contribute to physical properties of tissue

            -Help filter material passing between tissues

            -Help orient cell movements

            -Play a role in chemical signaling

Chapter 5 – The Dynamic Cell Membrane

5.1 What Is the Structure of a Biological Membrane?

            -general structure is known as fluid mosaic model (Nicholson & Singer)

            -phospholipid bilayer is like a “lake” in which a variety of proteins float

-membranes may vary in lipid composition: fatty acid chain length, degree of saturation, phosphate groups

            -membranes may be up to 25% cholesterol

Lipids constitute the bulk of a membrane

-phospholipid bilayer is flexible, and interior isfluid, allowing lateral movement of molecules

            -fluidity depends on temperature & lipid composition

Membrane proteins are asymmetrically distributed

            -Membranes contain proteins, the number of which varies with cell function

            -Some extend across the lipid bilayer, with hydrophobic & hydrophilic domains

            -Two types of membrane proteins:

-Integral membrane proteins: span the bilayer, hydrophilic ends protrude on either side, may have different domains on either side of membrane with very different properties

                        -Peripheral membrane proteins: do not penetrate bilayer

            -Proteins and lipids are independent and only interact noncovalently

-Some membrane proteins can move freely within the bilayer, while others are anchored to a specific region by cytoskeleton elements or lipid rafts (lipids in semisolid state)

Membrane carbohydrates are recognition sites

-Membranes have carbohydrates on outer surface that serve as recognition sites for other cells & molecules

5.2 How Is the Plasma Membrane Involved in Cell Adhesion and Recognition?

            -Cells arrange themselves in groups by cell recognition and cell adhesion

            -Processes studied in sponge cells: easily separated & come back together

Cell recognition and cell adhesion involves proteins at the cell surface

            -Binding of cells can be:

                        -Homotypic: same molecule sticks out from both cells & forms a bond

                        -Heterotypic: the cells have different proteins

Three types of cell junctions connect adjacent cells

-Cell junctions are specialized structures that hold cells together

                        -Tight junctions: specialized seals that link adjacent epithelial cells

                                    -prevent substances from moving through spaces between cells

-restrict migration of membrane proteins/phospholipids from one region of the cell to another

-Desmosomes: hold cells together; spot welds of cytoplasmic plaque  and adhesion proteins made of keratin fibers

                        -Gap junctions: allow communication between cells

-made of channel proteins called connexons, dissolved small molecules & ions can pass from cell to cell through these junctions

5.3 What Are the Passive Processes of Membrane Transport?

            -Membranes have selective permeability: some can pass through, others cannot

            -Passive transport: no outside energy required

            -Active transport: energy required

Diffusion is the process of random movement towards a state of equilibrium

-Diffusion: the process of random movement towards equilibrium, net movement is direction until equilibrium is reached

-Net movement from regions of greater concentration to regions of lesser concentration

-Diffusion rate depends on:

            -Diameter of molecules/ions

            -Temperature of solution

            -Electric charges

            -Concentration gradient

-Works well over short distances

-Membrane properties affect diffusion of solutes

            -Permeable to solutes that move easily across it

            -Impermeable to solutes that cannot move across it

Simple diffusion takes place through the phospholipid bilayer

            -Simple diffusion: small uncharged molecules pass through the lipid bilayer

            -lipid soluble molecules & water can diffuse across membrane

            -electrically charged & polar molecules cannot pass through easily

Osmosis is the diffusion of water across membranes

            -Osmosis: the diffusion of water; depends on number of solute particles present

            -always from hypotonic to hypertonic until both solutions are isotonic

                        -Isotonic: equal solute concentration

                        -Hypertonic: higher solute concentration

                        -Hypotonic: lower solute concentration

            -animal cells may burst when placed in hypotonic solution

-plant cells with rigid cell walls build up internal pressure to keep more water from entering – turgor pressure

Diffusion may be aided by channel proteins

-Facilitated diffusion: polar molecules can cross membrane through channel proteins and carrier proteins

            -Channel proteins: have central pore lined with polar amino acids

            -Ion channels: important channel proteins, most are gated; can be opened/closed to ion passage

            -gates open when protein is stimulated to change shape

                        -ligand-gated: protein changes shape due to molecule

                        -voltage-gated: electrical charge resulting from many ions

            -The K⁺ Channel selects K⁺ over Na⁺ when K⁺ is larger

                        -Both Na⁺ and K⁺ are attracted to polar H₂O

                        -In K⁺ channel, O atoms are located at a constriction

-K⁺ ion fits into constriction & gets into position where it is more strongly attracted to O atoms; K⁺ loses H₂O shell

                        -smaller Na⁺ ion is more distant from O atoms; therefore does not enter K⁺ channel

-Water passes through membrane by hydrating ions that pass through channel, or through special water channels called aquaporins

Carrier proteins aid diffusion by binding substances

            -Carrier proteins: transport polar molecules such as glucose across membranes

            -Glucose binds to protein, which causes it to change shape

5.4 How Do Substances Cross Membranes Against a Concentration Gradient?

Active transport is directional:

            -Active transport: moves substance against concentration gradient; requires energy

            -Uniports: moves one substance in one direction

            -Symports: moves two substances in the same direction

            -Antiports: moves two substances in opposite directions

Primary and secondary active transport rely on different energy sources

            -Primary active transport: requires direct participation of ATP

-Sodium-potassium pump: active transport, found in all animal cells; integral membrane glycoprotein, antiport

-Secondary active transport: energy comes from ion concentration gradient established by primary active transport

-Energy can be “regained” by letting ions move across membrane with concentration g         radient

-aids in uptake of amino acids and sugars

-uses symports & antiports

5.5 How Do Large Molecules Enter and Leave a Cell?

Macromolecules and particles enter the cell by endocytosis

            -Macromolecules (proteins, polysaccharides, nucleic acids) are too large to cross membrane

            -can be taken in or excreted by means of vesicles

            -Endocytosis: process that brings molecules/cells into eukaryotic cell

                        -Plasma membrane invaginates around material, forming vesicle

            -Phagocytosis: molecules or entire cells are engulfed

                        -some protists feed this way

                        -some white blood cells engulf foreign substances

                        -food vacule or phagosome forms, which fuses with lysosome to digest

            -Pinocytosis: vesicle forms to bring small dissolved substances or fluids into cell

                        -vesicles are much smaller than in phagocytosis

                        -constant in endothelial (capillary) cells

Receptor-mediated endocytosis is highly specific

            -Depends on receptor proteins: integral membrane proteins to bind to specific substances

            -sites are called coated pits – coated with other proteins such as clathrin

            -Mammalian cells take in cholesterol by receptor-mediated endocytosis

            -Lipids packaged by liver into lipoproteins à bloodstream

            -Liver takes low-density lipoproteins for recycling; LDLs bind to specific receptor proteins

Exocytosis moves materials out of the cell

            -Exocytosis: material in vesicles is expelled from cell

            -indigestible materials are expelled

            -other materials leave cells, such as digestive enzymes and neurotransmitters

Chapter 6 – Energy, Enzymes, and Metabolism

6.1 What Physical Principles Underlie Biological Energy Transformations?

The first law of thermodynamics: Energy is neither created nor destroyed

-When energy is converted from one form to another, the total energy before and after the conversion is the same

The second law of thermodynamics: disorder tends to increase

-When energy is converted from one form to another, some of that energy becomes unavailable to do work; entropy increases

            -no energy transformation is 100% efficient

Chemical reactions release or consume energy

            -Metabolism: sum total of all chemical reactions in an organism

            -Anabolic reactions: complex molecules are made from simple ones; energy input

            -Catabolic reactions: complex molecules are broken down into simpler ones; energy released

Chemical equilibrium and free energy are related

            ΔG = ΔH – TΔS

            -ΔG +, free energy is consumed; anabolic reactions

            -ΔG -, free energy is released, catabolic reactions

            -spontaneous processes always proceed to disorder

6.2 What is the Role of ATP in Biochemical Energetics?

ATP hydrolysis releases energy

            -ATP is a nucleotide; hydrolysis yields free energy

            -all living cells use adenosine triphosphate for capture, transfer, storage of energy

            -some of free energy released by exergonic reactions is captured in ATP

-not used exclusively to drive endergonic reactions; can also be converted into a building block for DNA/RNA

            ATP + H₂O à ADP + P_i + free energy, ΔG = -7.3 kcal/mol

ATP couples exergonic and endergonic reactions

            -Exogonic reaction: cell respiration, catabolism

            -Endergonic reaction: active transport, cell movements, anabolism

6.3 What Are Enzymes?

            -Catalysts speed up rate of reaction; catalyst itself not altered by reactions

            -Most biological catalysts are enzymes that act as a framework in which reactions can take place

For a reaction to occur, an energy barrier must be overcome

            -Activation energy (E_a): amount of energy required to start the reaction

-Activation energy changes reactants into unstable forms with higher free energy – transition state species

            -Can come from heating system (reactants have more KE)

-Enzymes lowers energy barrier by bringing reactants together. Final equilibrium does not change, ΔG does not change

Enzymes bind specific reactant molecules

            -Reactants are called substrates which bind to active sites of enzyme

            -3D shape of enzyme determines specificity

            -Most enzymes are much larger than substrate, active site only small region

            -Specificity of enzyme for a particular substrate depends on a precise interlock

            -1894, Emil Fischer compared the fit to lock and key

-1965, David Philips observed pocket in enzyme lysozyme that neatly fits its substrate using x-ray crystallography

Enzymes lower the energy barrier but do not affect equilibrium

-Enzyme-substrate complex is held together by hydrogen bonds, electrical attraction, or covalent bonds

E + S à ES à E + P

-Enzyme may change when bound to substrate, but returns to original shape

6.4 How Do Enzymes Work?

            -Enzymes orient substrate molecules, bringing together the atoms that will bond

            -Enzymes can stretch bonds in substrate molecules, making them unstable

            -Enzymes can temporarily add chemical groups to substrates

-Acid-base catalysis: enzyme side chains transfer H⁺ to/from substrate; break covalent bond

                        -Covalent catalysis: a functional group in a side chain bonds covalently with substrate

                        -Metal ion catalysis: metals on side chains lose or gain electrons

Molecular structure determines enzyme function

            -Shape of the enzyme’s active site allows specific substrate to fit

            -Induced fit: enzymes are thought to change shapes when they bind to substrate

-Best fit: enzymes exist in large variety of conformations; the conformation that provides the best fit binds the substrate

Some enzymes require other molecules in order to function

            -Prosthetic groups: non-amino acid groups permanently bound to enzymes (heme, flavin, retinal)

            -Cofactors: inorganic ions (iron, copper, zinc)

-Coenzymes: not bound permanently to enzymes, are changed in reaction (biotin, Coenzyme A, NAD, FAD, ATP)

Substrate concentration affects reaction rate

            -Rate of uncatalyzed reaction is proportional to concentration of reactants

            -Rate of catalyzed reactions level off due to saturation of enzyme

            -Turnover number: number of substrate molecules converted to product/unit time

            -Can range from 1 molecule ever 2 seconds for lysozyme, to 40 million/s for catalase

6.5 How Are Enzyme Activities Regulated?

Enzymes can be regulated by inhibitors

            -Inhibitors: molecule that binds to enzyme and slows reaction rates

            -naturally-occurring inhibitors regulate metabolism

-Irreversible inhibition: inhibitor covalently bonds to side chains in active site – permanently inactivates enzyme (nerve gas binds to OH on side chain of serine; prevents degredation of acetylcholine)

-Reversible inhibition: inhibitor binds noncovalently to active site

-Competitive inhibitors: similar to substrate, prevents substrate from binding to active site; when concentration is reduced, detaches from active site

-Noncompetitive inhibitors: binds to enzyme at different site; enzyme changes shape and alters active site

Allosteric enzymes control their activity by changing their shape

            -Allostery: some enzymes exist in more than one form

                        -Active form: can bind substrate

                        -Inactive form: cannot bind substrate but can bind inhibitor

            -Most allosteric enzymes have quaternary structure

                        -Catalytic subunit: has active site

                        -Regulatory subunits: where inhibitors and activators bind

Allosteric effects regulate metabolism

            -Metabolic pathways: first step is commitment step, everything else follows

-Final product may allosterically inhibit enzyme needed for commitment step & shuts down pathway – feedback inhibition or end-product inhibition

Enzymes are affected by their environment

-Every enzyme has optimal pH (depending on area of body) and temperature (usually body temperature)

Chapter 7 – Glycolysis and Cellular Respiration

7.1 How Does Glucose Oxidation Release Chemical Energy?

Cells trap free energy while metabolizing glucose

            C₆H₁₂O₆ + 6O₂ à 6CO₂ + 6H₂O + free energy

            ADP + P_i + free energy à ATP

            -Three metabolic processes play important roles

-Glycolysis: begins glucose metabolism & produces 2 molecules of pyruvate; small amount of energy stored in glucose is stored in usable forms; does not use O₂

-Cellular respiration: completely converts each pyruvate into 3 CO₂, great deal of energy stored in covalent bonds is released and transferred to ADP to form ATP; uses O₂

-Fermentation: converts pyruvate into lactic acid or ethanol; incomplete breakdown, less energy released; does not use O₂

An overview: harvesting energy from glucose

            -If O₂ is available: glycolysis, pyruvate oxidation, citric acid cycle, electron transport chain

            -If O₂ is not available: glycolysis, pyruvate metabolized in fermentation;

Redox reactions transfer electrons and energy

            -Coupled reaction, energy is transferred

            -Reducing agent is oxidized while oxidizing agent is reduced

The coenzyme NAD is a key electron carrier in redox reactions

            -NAD: nicotinamide adenine dinucleotide

            -exists in NAD⁺ (oxidized) and NADH + H⁺  (reduced)

                        NAD⁺ + 2H à NADH + H⁺

                        NADH + H⁺ + ½O₂ à NAD⁺ + H₂O

            -FAD: flavin adenine dinucleotide also transfers electrons

7.2 What Are the Aerobic Pathways of Glucose Metabolism?

-Glycolysis takes place in the cytosol

            -involves 10 enzyme-catalyzed reactions

            -results in: 2 molecules of pyruvate, 4 molecules of ATP (net 2), 2 molecules NADH

-Can be divided into two stages: energy-investing stage using ATP, energy-harvesting stage producing ATP

The energy-investing reactions of glycolysis require ATP

-in 2 separate reactions, two ATP molecules are used to make modification to glucose

-Phosphates from each ATP are added to carbon 6 and carbon 1 of the glucose molecule to ultimately form fructose 1,6-biphosphate

-The enzyme aldolase splits the molecule into two 3-C molecules that ultimately become glyceraldehyde 3-phosphate (G3P)

The energy-harvesting reactions of glycolysis yield NADH + H⁺ and ATP

-First reaction (oxidation) releases free energy used to make 2 molecules of NADH + H⁺, one for each of the two G3P molecules

-Two other reactions each yield one ATP per G3P molecule; substrate-level phosphorylation

-Third and final product is two 3-carbon molecules of pyruvate

Pyruvate oxidation links glycolysis and the citric acid cycle

            -Pyruvate is converted to acetyl CoA

            -Takes place in the mitochondrial matrix

            -Pyruvate is oxidized to acetate which is converted to acetyl CoA

-multistep reaction catalyzed by enzyme complex attached to the inner mitochondrial membrane

                        -acetyl group added to coenzyme A to form acetyl CoA; one NADH + H+ is generated

-Coenzyme A: nucleotide, vitamin, pantothenic acid, β-mercaptoethylamine, which binds the acetate molecule

The citric acid cycle completes the oxidation of glucose to CO₂

            -Acetyl CoA is the starting point of the citric acid cycle

            -Coenzyme A is removed and can be reused

            -Cycle in steady state: concentrations of intermediates don’t change

            -Output: CO₂, reduced electron carriers (NADH, FADH₂), ATP

The citric acid cycle is regulated by concentrations of starting materials

            -NADH and FADH₂ must be reoxidized before they take part in the citric acid cycle again

            -Fermentation: if no O₂ is present, pyruvate is reduced to lactate or ethanol

-Oxidative phosphorylation: if O₂ is present, then O₂ is reduced; pyruvate is fully oxidized to CO₂, and all NADH and FADH2 is reoxidized; energy released by oxidation is tapped to form ATP

7.3 How Is Energy Harvested from Glucose in the Absence of Oxygen?

            -Fermentation: occurs in cytosol

            -Pyruvate is reduced by NADH + H⁺ and NAD⁺ is regenerated

-Lactic acid fermentation: occurs in microorganisms, some muscle cells; pyruvate is the electron acceptor

            -Alcoholic fermentation: yeast and some plant cells

                        -Pyruvate is converted to acetaldehyde and CO₂ is released

                        -Acetaldehyde is reduced by NADH + H⁺, producing NAD⁺ and ethanol

7.4 How Does the Oxidation of Glucose form ATP?

-Oxidative phosphorylation: ATP is synthesized as electron carriers are reoxidized in the presence of O₂

            -Two stages: electron transport chain, chemiosmosis

-Electron transport chain has many steps because each step releases a small amount of energy that can be captured by an endergonic reaction

The electron transport chain shuttles electrons and releases energy

            -Occurs on the inner mitochondrial membrane

-4 protein complexes I (NADH-Q reductase), II (succinate dehydrogenase), III (cytochrome c reductase), IV (cytochrome c oxidase)

-Cytochrome c: small, peripheral protein that lies in the intermembrane space; loosely attached to inner mitochondrial membrane

-Ubiquinone (Q) – lipid; moves freely within the hydrophobic interior of the phospholipid bilayer of the inner mitochondrial membrane

-NADH + H+ passes through I, which passes electrons to Q; II passes electrons to Q from FADH2; III receives electrons from Q and passes them to cytochrome c; IV receives electrons from cytochrome c and passes them to oxygen, which picks up to H⁺ to form H₂O

-Electron transport chain results in active transport of H⁺ across the inner mitochondrial membranes; transmembrane complexes act as proton pumps

-Proton pump results in a proton concentration gradient and an electric charge difference across the inner membrane à potential energy called proton-motive force

Proton diffusion is coupled to ATP synthesis

-Protons must pass through a protein channel – ATP synthase – to flow back into mitochondrial matrix

            -Chemiosmosis is the coupling of the proton-motive force and ATP synthesis

-ATP synthase allows protons to diffuse back to the mitochondrial matrix, and uses the energy of diffusion to make ATP from ADP and P_i

            -ATP synthase

                        -F₀ subunit: transmembrane

-F₁ subunit: projects into mitochondrial matrix, rotates to expose active sites for ATP synthesis

-ATP synthesis can be uncoupled: if a different H+ diffusion channel is inserted into the mitochondrial membrane, the energy of diffusion is lost as heat

-the protein thermogenin occurs in human infants & hibernating animals; natural uncoupling protein plays important role in regulating the temperature of some mammals

7.5 Why Does Cellular Respiration Yield So Much More Energy Than Fermentation?

            -Energy yields:

                        -Glycolysis and fermentation: 2 ATP

                        -Glycolysis and cellular respiration: 32 ATP

-sometimes 30 due to some animal cells’ inner mitochondrial membrane impermeable to NADH, so one ATP must be used for each NADH to be shuttled into mitochondrial matrix

-Reason: fermentation byproducts have a lot of energy remaining remaining in the covalent bonds of lactate/ethanol

Chapter 8 – Photosynthesis: Energy from Sunlight

8.1 What Is Photosynthesis?

6CO₂ + 12H₂O à C₆H₁₂O₆ + 6O₂ + 6H₂O

            -Water is both consumed and produced, all oxygen produced comes from water

Photosynthesis involves two pathways

            -light reactions: light energy converted to chemical energy stored in ATP & NADPH + H⁺

-light-independent reactions: uses ATP and NADPH + H⁺ plus the reduction of CO₂ to produce sugars

-But because ATP and NADPH are not stored, both reactions must occur in the light

8.2 How Does Photosynthesis Convert Light Energy into Chemical Energy?

Light behaves as both a particle and a wave

            -Light is a form of electromagnetic radiation, comes in packets called photons

            -behaves as particles, and as if propogated like waves

            -energy of photon is inversely proportional to its wavelength

Absorbing a photon excites a pigment molecule

            -Photon à molecule can be:

                        -scattered or reflected

                        -transmitted or pass through molecule

-absorbed: molecule acquires energy of photon; goes from ground state to excited state

Absorbed wavelengths correlate with biological activity

            -photons can have a wide range of wavelengths and energy levels

            -pigments: molecules that absorb specific wavelengths in the visible range of the spectrum

            -absorption spectrum: plot of wavelengths absorbed by a pigment

-action spectrum: plot of biological activity as a function of wavelengths of light the organism is exposed to

Photosynthesis uses energy absorbed by several pigments

            -chlorophylls: a and b

-accessory pigments: carotenoids, phycobilins, absorb in red/blue regions, transfer energy to chlorophylls

Light absorption results in photochemical change

            -Pigment returns to ground state, energy may be given off as heat or fluorescence

            -fluorescence has longer wavelengths and less energy than absorbed light energy, no work is done

-Pigments can also pass energy to another molecule, which can be passed to a reaction center to be converted to chemical energy

-Pigments are arranged in antenna systems

            -packed together on thylakoid membrane proteins

-excitation energy is passed from pigments that absorb short wavelengths, to those that absorb longer wavelengths, and end up in the reaction center pigment

Excited chlorophylls in the reaction center acts as a reducing agent

            -Reaction center molecule is chlorophyll a

                        -absorbs light energy, transforms to chemical energy in the form of electrons

                        -transfers these electrons to other molecules

            -Excited chlorophyll (Chl*) is reducing agent (electron donor)

            Chl* + A à Chl⁺ + A^-

Reduction leads to electron transport

            -Final electron acceptor is NADP⁺ (nicotinamide adenine dinucleotide phosphate)

                        NADP⁺ + e^- à NADPH + H⁺

            -Noncyclic electron transport produces NADPH + H⁺ and ATP

            -cyclic electron transport produces ATP only

Noncyclic electron transport produces ATP and NADPH

            -Two photosystemsrequired in noncyclic electron transport

            -each photosystem consists of several chlorophyll and accessory pigment molecules

-photosystems complement each other; must be constantly absorbing light energy to power noncyclic electron transport

-Photosystem I:

            -Light energy reduces NADP⁺ to NADPH + H⁺

            -Reaction center is chlorophyll a molecule P₇₀₀ (absorbs in 700 nm range)

-Photosystem II:

            -Light energy oxidizes water à O₂, H⁺, and electrons

            -Reaction center is chlorophyll a molecule P₆₈₀ (absorbs at 680 nm)

-Z scheme model describes noncyclic electron transport

-Chain reactions in electron transport chain are coupled to proton pump that results in chemiosmotic formation of ATP

            -Noncyclic electron transport yields NADPH + H⁺, ATP, O₂

Cyclic electron transport produces ATP but no NADPH

-Cyclic electron transport: electron from excited chlorophyll cycles back to same chlorophyll molecule

-A series of exergonic redox reactions, released energy creates proton gradient used to synthesize ATP

Chemiosmosis is the source of the ATP produced in photophosphorylation

            -Photophosphorylation: light-driven production of ATP

-Electron transport is coupled with transport of H⁺ across thylakoid membrane (from stroma into lumen)

8.3 How Is Chemical Energy Used to Synthesize Carbohydrates?

            CO₂ fixation: CO₂ is reduced to carbohydrates

            -enzymes in stroma uses energy in ATP and NADH to reduce CO₂

-because ATP/NADPH are not stored, these light-independent reactions must also take place in the light

Radioisotope labeling experiments revealed the steps of the Calvin cycle

-Calvin and Benson used the ¹⁴C radioisotope to determine sequence of reactions in CO₂ fixation

-Exposed Chlorella to ¹⁴CO₂, then extracted organic compounds and separated by paper chromatography

-3-second exposure of Chlorella to ¹⁴CO₂ revealed tat first compound to be formed is 3PG (3-phosphoglycerate)

-initial reaction fixes one CO₂ into 5-C compound: ribulose 1,5-biphosphate (RuBP)

-intermediate 6-C compound forms, unstable and breaks down into two 3PG

-enzyme that catalyzes fixation of CO₂ is ribulose biphosphate carboxylase (rubisco), most abundant protein in the world

The Calvin cycle is made up of three processes

            -Fixation of CO₂, combination with RuBP catalyzed by rubisco

-Conversion of fixed CO₂ into carbohydrate – glyceraldehyde 3-phosphate (G3P), uses ATP and NADPH

            -Regeneration of CO₂ acceptor RuBP by ATP

-5/6 of G3P is recycled into RuBP

-1/6 of G3P forms starch (1/3) and sucrose (2/3), which is hydrolyzed to glucose and fructose

-Covalent bonds in carbohydrates produced in the Calvin cycle represent the total energy yield of photosynthesis

-this energy is used by the autotrophs themselves, and heterotrophs who cannot photosynthesize

Light stimulates the Calvin cycle

-Proton pumping from stroma into thylakoid increases pH, which favors activation of rubisco

-Electron flow from photosystem I reduces disulfide bonds to activate Calvin cycle enzymes

-Rubisco is oxygenase as well as a carboxylase

-can add O₂ to RuBP instead of CO₂, reduce amount of CO₂ fixed, and limit plant growth; product: 3PG and phosphoglycolate

8.5 How Is Photosynthesis Connected to Other Metabolic Pathways in Plants?

            -Photosynthesis and respiration are linked by Calvin cycle

-Glycolysis in cytosol, respiration in mitochondria, and photosyntehsis in chloroplasts can occur simultaneously

Chapter 40 – Physiology, Homeostasis, and Temperature Regulation

40.1 Why Must Animals Regulate Their Internal Environments?

-Extracellular fluid constitutes internal environment

-Extracellular fluid interacts directly with each cell: provide nutrients, accept waste, vehicle for communication

            -Each cell must be near water environment, must be constant, homeostatis

An internal environment makes complex multicellular animals possible

            -Evolution of multicellular organisms allowed specialization of functions

            -Each cell did not have to perform the same functions

            -Cells insulated from external environment

            -Specialization: salt/water balance, nutrients, gamete production, exchange

            -Control and regulation needed         (nervous & endocrine systems)

Homeostasis requires physiological regulation

-Feedback: comparison of variable to be regulated with set point; error, change control of generator

            -Feedforward: change in set points based on anticipation of changing conditions

            -Types of information necessary for physiological systems:

            -set point: reference point

            -feedback information: what is happening to the system

            -error signal: difference between set point and feedback information

-Sensory information in regulatory systems include:

-Negative feedback: feedback info causes effectors to reduce/reverse the process or counteract the influence that created an error signal, returns variable to set point

-Positive feedback: amplifies response; increases deviation from set point

-Feedback information: anticipates internal changes and changes set point

40.2 How Does Temperature Affect Living Systems?

            -Proteins denature above 45°C

            -Most cells function between 0-45°C

Q₁₀ is a measure of temperature sensitivity

-Q₁₀: rate of reaction at one temperature divided by rate at ten degrees lower; measure sensitivity of process to temperature, =2-3 for most biological reactions

                        Q₁₀ = R_T/(R_T – 10)

            -Difficult for animal to change in temperature because each process has different Q₁₀

            -compensate for change in temperature or prevent it

Animals can acclimatize to a seasonal temperature change

-Ex: summer fish vs. winter fish

                        -Fish’s metabolic rate may be similar in winter and summer

-Fish acclimatized by regulating use of two different enzymes (same function, but different temperature optima) as well as metabolic compensation

            -Metabolic compensation: result is metabolic rate is less sensitive to temperature

            -Not passive change implied by Q10, but active, compensates for change in environment

40.3 How Do Animals Alter Their Heat Exchange with the Environments?

            Thermal classification of animals based on source of heat

-Ectotherms have external sources of heat; depends on external sources of heat: fish, amphibians, reptiles

-Endotherms regulate body temperature by producing heat metabolically or by actively losing heat: mammals, birds

                        -Heterotherms can behave as either ectotherm or endotherm

            Major differences between ectotherms and endotherms:

-Resting metabolic rate, total energy expenditure at rest, response to changes in environemental temperature

How do endotherms produce so much heat?

            -Major differences between ectotherms and endotherms:

-Resting metabolic rate, total energy expenditure at rest, response to changes in environemental temperature

Ectotherms and endotherms react differently to changes in temperature

            -Experiment I: measure body temperature as function as function of external temperature

                        -Lizard’s body temperature tracks environmental temperature closely

-Mouse’s body temperature constant over wide range of environmental temperatures

            -Experiment II: measure of lizard body temperature in the wild

-Lizard’s body temperature is relatively constant, even though environmental temperature changes

            -Both ectotherms and endotherms can alter heat exchange between body/environment

-Body temperature determined by balance between internal heat production and four types of heat exchange

Energy budgets reflect adaptations for regulating body temperature

            -Four types of heat exchange

                        -Radiation: heat transfer via infrared radiation

                        -Conduction: heat transfer by direct contact

                        -Convection: heat transfer through a surrounding medium

                        -Evaporation: heat transfer through evaporation of water from a surface

Methods of regulating body temperature

            -Behavioral: bask in sun, use of burrows, clothing

            -Control of blood flow to skin:

                        -Vasodilation allows rapid heat uptake/los

                        -Vasoconstriction reduces heat flow in/out

                        -increase in heart rate increases heat gain or loss

            -Some ectotherms produce heat

                        -Isometric contraction of muscles in insects

                        -honeybees gather in brood area to increase warmth

                        -python female wraps around eggs and does isometric contractions

            -Hot fish vs cold fish: vascular adaptations reduce heat loss to water

-Hot fish: small aorta and countercurrent flow in arteries and veins to retain heat in muscles; heart allows much more powerful muscular contractions

-Cold fish: pumps blood from heart to gills (across thin membrane from water), has large dorsal aorta

40.4 How Do Mammals Regulate Their Body Temperatures?

Basal metabolic rates are correlated with body size and environmental temperature

-Thermoneutral zone: range of environmental temperatures over which metabolic rate is low and independent of environmental temperature

-Basal metabolic rate: resting rate in this zone; 6x higher in endotherms than ectotherms of same mass

-Evolution of endothermy brought much higher capacity for energy consumption and heat production

            -Edges of thermoneutral zone are upper & lower critical temperatures

                        -Above: animals uses energy to sweat, pant

-Below: animal shivers to produce heat, consume ATP but little change in muscle length, or brown fat, high mitochondria + protein thermogenin uncouples oxidative phosphorylation to consume fuel but make no ATP

            -BMR is correlated with body size and environmental temperature

                        -BMR per gram of tissue increases as animal gets smaller

                        -a gram of mouse tissue uses energy 20x greater than a gram of elephant tissue

            -Thermoregulation in endotherms

-Cold climates: thermal insulation (fur), body shape (reduce SA/V ratio, decrease body flow to skin)

                        -Hot climates: water evaporation, sweating & panting, surface vasodilation

The vertebrate thermostat uses feedback information

            -Cool hypothalamus with temperature probe (leaving body temperature unchanged)

                        -Fish/reptiles seek warmer water

                        -Mammals constrict blood vessels to skin

            -Hypothalamic temperature is negative feedback signal rather than set point

            -Set point is in hypothalamus

-Different set points for different responses to cooling: begin cooling, first induces constriction of blood vessels, further cooling induces shivering

            -Amount of metabolic heat production proportional to magnitude of cooling

            -Thermostat integrates other information

                        -Temperature sensors in skin alter the set point

                        -Warm environment: need to cool hypothalamus to cause shivering

                        -Cold environment, same body temp: shiver without any cooling

                        -Set point changes with environmental temperature, sleeping vs waking

Fever helps the body fight infections

            -Pyrogens cause rise in temperature

            -Endogenous pyrogens from immune system

            -Exogenous pyrogens from baceria, viruses

            -Fever is adaptive response, helps fight pathogens

            -Pyrogens increase hypothalamic set point, cause shivering

            -Aspirin and acetaminophen reduces set point

            -Mechanism of aspirin action

                        -Pyrogens attacked by macrophages

                        -Macrophages release interleukins

-Interleukins act in brain, raise hypothalamus set point by stimulating prostaglandins, increase temperature = fever

-Aspirin reduces prostaglandin synthesis; blocks interleukin effect on hypothalamus, recduces fever

Turning down the thermostat

-Torpor: lowering of set point for body temperature adaptation for small animals in cold climate to reduce energy requirements

            -Hibernation: regulated hypothermia that lasts for days (even weeks), deep sleep

Chapter 41 – Animal Hormones

41.1 What Are Hormones and How Do They Work?

            -Control & regulation require information

            -Communication: feedback, coordination, feedforward, regulation, control

            -Endocrine: inside secretion; slow in contrast with nervous system

-Cells communicate with target cells that have receptors/specializations that respond to hormones

Hormones can act locally or at a distance

            -Endocrine cells: cells that secrete hormones

            -Target cells: cells that have receptors for the hormones

            -Hormones: chemical signals secreted by cells of the endocrine system

-Classical definition of hormone: molecule that is secreted into blood and is carried to distant target organ where it acts, slow; contrast with neurotransmitter which is released locally to act on adjacent cell, fast

-Recent definition: hormones do not need to enter bloodstream. Can act on adjacent cell (paracrine) or cell that synthesizes the hormone (autocrine); neurotransmitters act across specialized synaptic junctions with specialized presynaptic and postsynaptic structures; hormones only require a receptor

-Circulating hormones: secreted into extracellular fluid, diffused into blood, and distributed through body to target cells far from site of release

-Paracrine hormone: affect target cells near the site of release

-Autocrine hormone: affect cells that released the hormones

-Advantages of hormone as signal method

-Broadcast widely; different tissues can possibly evolve sensitivity to hormones to coordinate activity with secreting organ

-Ex. 1: testosterone (secreted when testes make sperm)

-acts on many tissues that need to be active during reproduction: muscles, brain, liver, penis, vas deferens

            -each tissue evolved ability to respond to the single signal

-Ex. 2: epinephrine (adrenalin from adrenal)

            -Fight or flight response; released by fear-provoking stimulus

            -speeds heart rate & strength of contractions

            -constricts blood vessels to gut, increase blood to muscles

            -stimulates glycogen breakdown to glucose for quick energy

            -stimulates breakdown of fat as source of energy

            -Hormones function to coordinate the activity of different organs and tissues

-Hormonal molecules are reused during evolution; same hormone and receptor system may serve different purposes in different animals

            -Ex. 3: prolactin (stimulates mammary tissue to produce milk in mammals)

-Pigeons/doves: causes production of “crop milk” (sloughed off lining of crop regurgitated to feed young) in pigeons/doves

                        -Amphibians: prepare for reproduction by seeking water

-Fish: regulate osmotic balance during migration of salmon from salt to fresh water

Hormones can be divided into three chemical groups

-Protein/peptide: water soluble, do not cross cell membrane, cell surface receptors; insulin, growth hormone

-Steroids: derived from cholesterol, lipid, cross cell membranes, nuclear receptor; estradiol, testosterone, cortisol

            -Amines: some are water and others are lipid soluble; thyroxine, epinephrine

Hormone receptors are found on the cell surface or in the cell interior

-Hormones have access to many cells, but only influence cells that have a receptor for the hormone

-Binding to receptor usually required for action of hormone; triggers downstream cellular/molecular events

            -Receptors can be on cell surface or inside the cell

            -Receptor sites differ for different hormones

                        -Lipid-soluble hormones: receptors inside the cell

-Water soluble hormones: receptors outside cell, since hormones cannot readily pass cell membrane

41.2 How Do the Nervous and Endocrine Systems Interact?

The pituitary gland connects nervous and endocrine functions

            -Pituitary gland: sits at base of brain for easy communication

            -two parts in humans: anterior and posterior

            -Control of posterior: neural

            -Control of anterior: hormonal

-Posterior pituitary: hypothalamic neurons whose endings are in the posterior pituitary secrete oxytocin and vasopressin (ADH)

-Oxytocin: secreted during labor of childbirth, increases uterine contraction

-baby’s suckling stimulates release of oxytocin; causes milk to let down and flow from the breast

-adults who received oxytocin via nasal spray showed more trust in psychological tests

-Vasopressin (ADH): secreted when blood pressure falls or blood too salty

-increases absorption of water in kidney, increases retention of water to increase blood volume and dilute blood; aka anti-diuretic hormone

            -increases blood pressure by constricting blood vessels

            -alcohol inhibits ADH, blood loss increases ADH

-Anterior pituitary releases four peptide/protein hormones

            -They are tropic hormones (control activities of other endocrine glands)

                        -Luteinizing hormone: causes ovulation

-Follicle stimulating hormone: growth of ovarian follicle; stimulates sex steroid secretion

-Adreno cortico trophic hormone (ACTH): growth of adrenal cortex; induces secretion of cortical glucocorticoids

            -Thyrotropin: causes secretion of thyroxine from thyroid gland

The anterior pituitary is controlled by hypothalamic hormones

            -Three organ relationship: hypothalamo-pituitary-gonadal axis

                        -Hypothalamus secrets gonadotrophin releasing hormone (GnRH)

                        -GnRH acts on anterior pituitary to cause secretion of gonadotrophins LH/FSH

                        -Gonadotrophins act on ovary to cause secretion of estradiol

                        -Estradiol acts on hypothalamus to inhibit secretion of GnRH

            -Three organ relationship: hypothalamus – anterior pituitary – adrenal

                        -Hypothalamus secretes CRF to stimulate anterior pituitary

                        -Anterior pituitary secretes ACTH to stimulate adrenal

                        -Adrenal releases cortisol, which inhibits hypothalamus secretion of CRF

            -Three organ systems: hypothalamus – anterior pituitary – thyroid

                        -Hypothalamus secretes TRH to stimulate anterior pituitary

                        -Anterior pituitary secretes thyrotropin to stimulate thyroid

                        -Thyroid releases thyroxine which inhibits hypothalamus secretion of TRH

            -Negative feedback loop

            -Other anterior pituitary hormones

-Growth hormones: act on tissues to promote growth; stimulates liver to produce somatomedins which causes growth of bone

                        -Prolactin: stimulates production/secretion of milk; growth of mammary tissues

                        -Melanocyte stimulating hormone: unknown function in humans

-Endorphins/enkephalins: endogenous opiates in grain; pituitary secretion function unknown

41.3 What Are the Major Mammalian Endocrine Glands and Hormones?

Thyroxine controls cell metabolism

            -Thyroid gland: secretes thyroxine (T4) and triiodothyronine (T3), forms of thyroxine

            -elevates metabolic rate, promotes use of carbohydrates in preference to fats

            -cold stress increases thyroxine secretion

            -important during growth/development; increases amino acid uptake & protein synthesis

-Cretinism: insufficient thyroxine leads to serious physical deficiencies in physical and mental growth

-Brain uses body temperature and day length to determine levels of TRH

Thyroid dysfunction causes goiter (enlarged thyroid)

            -Hyperthyroid goiter: failure of negative feedback

-Autoimmune disease Ab against thyrotropin receptor;  bind to thyroid cells and induces them to release thyroxine; thyroid is stimulated and grows

-Pituitary tumor: overpowers thyrotropin or hypothalamic tumor overproduces TRH; high thyrotropin stimulates overgrowth of thyroid

-Leads to high metabolic rate, jumpiness, nervous, hot

            -Hypothyroid goiter: lack of dietary iodine

                        -Lack of thyroxine à lack of negative feedback, so thyrotropin levels are high

                        -Low metabolism, intolerance of cold, physica/mental sluggishness

Calcitonin reduces blood calcium

Parathyroid hormone elevates blood calcium

Vitamin D is really a hormone

PTH lowers blood phosphate levels

Insulin and glucagon regulates blood glucose levels

            -Insulin: secreted from beta cells in Islet of Langerhans in pancreas; 51aa protein

                        -binds to surface receptors on cell membranes

                        -induces cells to take up glucose & store as glycogen and fat

-eating triggers insulin secretion b/c of need to store glucose; insulin causes uptake of glucose from blood and stores

            -Glucagon: secreted by alpha cells in the Islets of Langerhans in pancreas

                        -Opposite effects of insulin

                        -secreted when blood sugar falls well below normal

                        -causes breakdown of glycogen into glucose; release of glucose into blood

            -Diabetes: failure of action of insulin

-Type I: autoimmune disease destroys insulin-secreting cells in pancreas; juvenile onset

-Type II: loss of insulin receptors, increased by high fat diet and lack of exercise; adult onset

            -Diabetes mellitus: copious production of sweet urine

                        -lack of insulin because of autoimmune attack on beta islet cells of pancreas

-cells cannot take up glucose; body wastes away because it can only use energy from fat and brain

-lack of glucose uptake from blood means high blood sugar that is excreted by the kidney; sweet urine

Somatostatin is a hormone of the brain and the gut

            -Somatostatin: released from delta cells of pancreas

                        -response to rapid rises of glucose and amino acids

                        -has paracrine functions in Islets to inhibit release of insulin and glucagon

                        -decreases contractions in gut; increase the time nutrients are absorbed from gut

The adrenal gland is two glands in one

-Adrenal medulla (inside): secretes epinephrine (adrenalin) and norepinephrine (noradrenalin)

-Epinephrine: is amine, hydrophilic, acts on cell surface receptors; increases heart rate, blood pressure, diverts blood to muscles

                        -Two kinds of receptors: alpha and beta adrenergic

-Adrenal cortex (outside): secretes corticosteroids: glucocorticoids (cortisol), mineralocorticoids (aldosterone), and sex steroids

                        -Glucocorticoids: involved in glucose metabolism; increased by stress

-brain/muscle need glucose; cortisol stimulates other cells to decrease use of glucose & metabolize fats and proteins, release glucose, inhibit inflammation

-long term disadvantage: kills brain cells, loss of immune function, wasting of muscles, elevated blood pressure, elevated fat metabolism

                        -Mineralocorticoids: involved in mineral balance

The sex steroids are produced by the gonads

-Gonads: Testes (male) & Ovaries (female)

                        -Testes: site of production/maturation of sperm

                        -Leydig cells secrete testosterone (steroid hormone)

-Testosterone: causes growth and differentiation of masculine structures, sex drive, aggressiveness, production of sperm, hair growth, muscle mass

                        -Ovaries: site of production/maturation of egg cells

                        -Major hormones: estrogens (estradiol) and progestins (progesterone)

-Estrogens: cause enlargement of breasts, cellular changes in vagina/uterus, increase in subcutaneous fat, control of ovulation

                        -Progesterone: prepares uterus for implantation of embryo; behavioral effects

41.4 How Do We Study Mechanisms of Hormone Action?

Hormone action: general principles of mechanism

-small number of hormone molecules have large effect: amplification of hormone action occurs at target; one molecule of epinephrine releases millions of molecules of glucose from liver cell

            -Hormones act via binding to receptor proteins

-Expression of receptor by specific cell types determines which cells can respond to hormone

            -Functional effects of hormones determined by post-receptor mechanisms

-Regulation of receptors by other factors can turn on/shut off cell’s response to the hormone depending on body needs

Hormones can be detected and measured with immunoassays

A hormone can act through many receptors

-Protein/peptide/glycoprotein: hydrophilic, do not enter cell, bind to receptor on outside membrane of cell

-Steroid: lipophilic, hydrophobic, pass through cell membrane and bind to intracellular receptor

-Steroids: androgens (testosterone), estrogens (estradiol), progestins (progesterone), glucocorticoids (cortisol), mineralocorticoids (aldosterone)

-Pass through cell wall, meet soluble cytoplasmic/nuclear

-Ex.1: testosterone binds to androgen receptor (AR); causes change in conformation of AR, causing it to bind to DNA in nuclease at androgen response element; then increase/decrease DNA transcription into mRNA

-steroids turn genes on/off; specific genes depend on cell type

-Ex.2: Human XY individual with Androgen Insensitivity; Y chromosome present, androgen secreted, but androgen receptors absent à no androgen action à feminine development of genitals

            -Three domains of receptor

                        -Extracellular: binds hormone on outside

                        -Membrane spanning: lipophilic

                        -Intracellular: catalytic domain in cytoplasm

            -Mechanism of action

                        -binding of hormone activates protein kinases directly/indirectly

                        -protein kinases activates/inactivate proteins by phosphorylation

-phosphorylation is transfer of phosphate from ATP to protein, can activate/inactivate protein, enzyme kinase

                        -hormone signal is transduced to change in cell

A hormone can act through different signal transduction pathways

            -Receptors can be linked to different signal transduction pathways

-ex: epinephrine & norepinephrine connect with different pathways, can have different effects in the same cell

            -Signal transduction pathways can be “cascades” (each step amplifies response)

                        -one hormone molecule binding to receptor à 10⁶ molecules of final product

Chapter 44 – Neurons and Nervous Systems

44.1 What Cells Are Unique to the Nervous System?

            -Neurons generate and propagate electrical signals called action potentials

            -Glial cells provide support and maintain extracellular environment

Neuronal networks range in complexity

            -Neurons are organized into networks

            -Nerve net: simple network of neurons (in cnidarians)

            -Ganglia: neurons organized into clusters, sometimes in pairs

-Brain: largest pair of ganglia (as animals increase in complexity, one pair of ganglia is larger than others)

-Central nervous system (CNS): cells found in brain and spinal cord

-Peripheral nervous system (PNS): neurons /support cells found outside CNS

-brains vary in size; humans have large cerebrum, small olfactory lobe

Neurons are the functional units of nervous systems

            -Neurons are individual cells that make up nerves

            -Most have four regions

                        -Cell body: nucleus & organelles

                        -Dendrites: bring information to cell body

                        -Axons: carry information away from cell body

                        -Axon terminal: forms synapse at tip of axon

            -Neurons pass information using neurotransmitters at synapses

                        -Presynaptic neuron sends the message

                        -Postsynaptic neuron receives message

Glial cells are also important components of nervous systems

            -Glial cells outnumber neurons in the brain

            -they do not transmit electrical signals but have several functions

                        -Support during development

                        -Supply nutrients

                        -Maintain extracellular environment

                        -Insulate axons

            -Types of glial cells

                        -Oligodendrocytes produce myelin & insulate axons in the CNS

                        -Schwann cells insulate axons in the PNS

                        -Astrocytes contribute to the blood-brain barrier to protect the brain

44.2 How Do Neurons Generate and Conduct Signals?

            -Action potentials are the result of ions moving across the plasma membrane

            -ions move according to differences in concentration gradients and electrical charge

-Membrane potential is the electric potential across the membrane

            -Resting potential is the membrane potential of a resting neuron

Simple electrical concepts underlie neuronal function

            -Voltage causes electric current as ions to move across cell membranes

            -major ions in neurons: Na⁺, K⁺, Ca²⁺, Cl^-

Membrane potentials can be measured with electrodes

            -Membrane potentials are measured with electrodes

            -resting potential of axon is -60 to -70 mV

-inside of cell is negative at rest, relative to the outside; action potential allows positive ions to flow in briefly, making the inside of cell more positive

Ion pumps and channels generate membrane potentials

-plasma membrane contains ion channels and ion pumps that create resting & action potentials

-Sodium-potassium pump uses ATP to move Na⁺ ions from the inside and exchanges them for K⁺ from the outside of the cell; establishes concentration gradient for Na⁺ and K⁺

-Ion channels are selective & allow some ions to pass more easily

-direction & size of ion movement depends on concentration gradient & voltage difference of the membrane

-Two forces acting on an ion = electrochemical gradient

-Potassium channels are open in the resting membrane; highly permeable to K⁺ ions

-K⁺ ions diffuse out of cell along concentration gradient; leave behind negative charges

-K⁺ ions diffuse back into cell because of negative electrical potential

-Potassium equilibrium potential is the membrane potential at which the net movement of K⁺ ceases

-Nernst equation calculates value of potassium equilibrium potential by measuring the concentration of K⁺ on both sides of membrane

Gated ion channels alter membrane potential

            -Some ion channels are gated, & open/close under certain conditions

            -Voltage-gated channels respond to change in voltage across membrane

            -Chemically gated channels depend on molecules that bind/alter the channel protein

            -Mechanically-gated channels respond to force applied to the membrane

            -Gated ion channels change the resting potential when they open and close

            -Membrane is depolarized when Na⁺ enters cell; inside is less negative than rest

-Membrane is hyperpolarized if gated K⁺ channels open and K⁺ leaves; cell becomes more negative inside

Sudden changes in Na⁺ and K⁺ channels generate action potentials

            -Action potentials are sudden, large changes in membrane potentials

            -voltage-gated Na+ and K+ channels are responsible for action potentials

-If cell body is depolarized, voltage-gated Na⁺ channels open and Na⁺ rushes into axon; influx of cations causes more depolarization

-Threshold is reached at 5-10 mV above resting potential; influx of Na⁺ is not offset by outward movement of K⁺

-Many voltage gated Na⁺ channels open; membrane potential becomes positive, and action potential occurs

-Axons return to resting potential as voltage-gated Na⁺ channels close and voltage-gated K⁺ channels open

-K⁺ channels open more slowly and stay open longer, allowing K⁺ to carry excess charges out of axon; membrane potential returns to negative value and becomes more negative than resting potential until all voltage-gated K⁺ channels close

-Voltage gated Na+ channels have a refractory period in which they cannot open

-This property can be explained by the channels having two gates

            -Activation gate: closed at rest, but opens quickly at threshold

-Inactivation gate: open at rest, and closes at threshold but responds more slowly; gate reopens 1-2ms later than the activation gate closing

            -Voltage-gated K⁺ channels contribute to refractory period by remaining open

-efflux of K⁺ ions makes membrane potential less negative than resting potential for brief period of time

            -Dip after action potential is called hyperpolarization or undershoot

Action potentials are conducted along axons without loss of signal

-Action potential is all-or-none event because voltage-gated Na+ channels have a positive feedback mechanism that ensures the maximum value of the action potential

-Action potential is self-regenerating because it spreads to adjacent membrane regions; resulting depolarization brings neighboring areas of membrane to threshold; action potential occurring at one location on axon stimulates the adjacent region of axon to generate an action potential

-Action potentials travel faster in myelinated and large-diameter axons

Action potentials can jump along axons

            -Myelination by glial cells increases the conduction velocity of axons

            -the nodes of Ranvier are regularly spaced gaps where the axon is not covered by myelin

-Action potentials are generated at the nodes and positive current flow down the inside of the axon

-When the positive current reaches the next node, the membrane is depolarized and another axon potential is generated

            -Action potentials seem to jump from node to node; propagation = salutatory conduction

44.3 How Do Neurons Communicate with Other Cells?

            -Synapse: where neurons communicate with other neurons or target cells

-Chemical synapse: chemicals from presynaptic cell induce changes in postsynaptic cell

                        -Electrical synapse: action potential spreads directly to the postsynaptic cell

The neuromuscular junction is a model chemical synapse

-Neuromuscular junction is a chemical synapse between motor neurons and skeletal muscles

            -Motor neuron releases acetylcholine (ACh) from axon terminals

            -Postsynaptic membrane of muscle cell is the motor end plate

            -Synaptic cleft is space between presynaptic & postsynaptic membrane

The arrival of an action potential causes the release of a neurotransmitter

-Action potential causes release of ACh when voltage gated Ca²⁺ channels open & Ca²⁺ enters the axon terminal; vesicless release ACh into synaptic cleft

The postsynaptic membrane responds to neurotransmitter

-Postsynaptic membrane responds to ACh

-ACh diffuses across the cleft and binds to ACh receptors on the motor end plate

            -Receptors allow Na⁺ and K⁺ to flow through & increase in Na⁺ depolarizes membrane

-Depolarization of membrane activates firing of an action potential, which is conducted throughout the muscle cell’s membranes, causing the cell to contract

Synapses between neurons can be excitatory or inhibitory

-Synapses between motor neurons and muscle cells are excitatory; ACh always causes depolarization

            -Other synapses can be inhibitory if postsynaptic response is hyperpolarization

            -Neuron has many synapses & may receive many different chemical messages

The postsynaptic cell sums excitatory and inhibitory input

Synapses can be fast or slow

            -Receptors in postsynaptic cells open/close ion channels

-Ionotropic receptors are ion channels; neurotransmitter binding cause direct change in ion flow; response are fast & short-lived

-Metabotropic receptors induce signaling cascades that lead to changes in ion channels; responses are slower & longer-lived

                        -receptor activates intracellular signaling reactions that open/close ion channels

The action of a neurotransmitter depends on the receptor to which it binds

            -Major neurotransmitters in the CNS

                        -ACh (acetylcholine) in skeletal muscles & CNS

                        -Glutamate – excitatory amino acid

                        -Glycine & GABA (gamma amino butyric acid) – inhibitory amino acid

                        -Monoamines

                        -Peptides

            -Each neurotransmitter has multiple receptor types

            -ACh has two:

                        -Nicotinic receptors are ionotropic and excitatory

                        -Muscarinic receptors are metabotropic and inhibitory

To turn off responses, synapses must be cleared of neurotransmitter

-Neurotransmitters are cleared from the cleft after release in order to stop their action in several ways

                        -Diffusion away from cleft

                        -Reuptake by adjacent cells via active transport

-Enzymes present in the cleft may destroy them (ex acetylcholinesterase acts on ACh)

Chapter 45 – Sensory Systems

45.1 How Do Sensory Cells Convert Stimuli into Action Potentials?

            -Sensory cells transducer physical/chemical stimuli into neuronal signals

Sensory receptor proteins act on ion channels

            -Sensory transduction begins with a receptor protein that can detect a specific stimulus

            -Receptor protein opens/closes ion channels in the membrane, changing resting potential

            -Sensory receptor proteins can be:

-Ionotropic: ion channels themselves or directly affect ion channels: mechanoreceptors, thermoreceptors, electrosensors

-Metabotropic: affect ion channels through G proteins and second messengers: chemoreceptors, photoreceptors

Sensory transduction involves changes in membrane potentials

            -Sensory receptor cells transducer energy of stimulus into change in membrane potential

-Receptor potential generates action potential in receptor cell or causes release of neurotransmitter

Sensation depends on which neurons receive action potentials from sensory cells

-Some sensory receptor cells are organized with other cells in sensory organs

-Sensory systems include sensory cells, associated structures, and neuronal networks that process the information

Many receptors adapt to repeated stimulation

-Adaptation: sensory cells give gradually diminishing responses to maintained or repeated stimulation; enable animals to ignore background/unchanging conditions while remaining sensitive to changes or new information

45.2 How Do Sensory Systems Detect Chemical Stimuli?

            -Chemoreceptors: receptor proteins that bind various ligands; responsible for taste/smell

            -Also monitor internal environment, such as CO₂ levels in blood

Arthropods provide good examples for studying chemoreception

            -Pheromones are chemical signals used by insects to attract mates

-ex: female silkworm moth releases bombykol; male has receptors for bombykol on antennae; one molecule of bombykol is enough to generate action potentials

Olfaction is the sense of smell

            -Olfaction: sense of smell

            -Olfactory sensors are embedded in epithelial tissue at top of nasal cavity (in vertebrates)

-Axons extend to the olfactory bulb in the brain; dendrites end in olfactory hairs on the nasal epithelium

-Odorant: molecule that binds to receptor protein on olfactory cilia

-Olfactory receptor proteins are specific for particular odorants

-When odorant binds to receptor protein, it activates a G protein, which activates a second messenger (cAMP)

-Second messenger binds to cation channels in plasma membrane; generates action potential in the sensory neuron

-More odorants can be discriminated than there are olfactory receptors

-In olfactory bulb, axons from neurons with the same receptors converge on glomeruli

            -complex odorants can activate a unique combination of glomeruli

Gustation is the sense of taste

            -Gustation: sense of taste

            -Taste buds are clusters of chemoreceptors

            -Human taste buds are embedded in the tongue epithelium, on the papillae

            -some fish have taste buds on skin; duck-billed platypus has taste buds on the bill

            -Tongue epithelium is shed/replaced at a rapid rate

            -Taste bud cells last about 10 days

            -Neurons form new synapses with new taste bud cells as they are formed

            -Humans taste five flavors: salty, sour, sweet, bitter, and umami (receptors for amino acids)

            -Full complexity of taste involves both gustatory and olfactory receptors

            -Saltiness receptors are ionotropic

            -Sweet/bitter receptors are metabotropic

-Change in membrane potential of receptor cells causes release of neurotransmitters onto dendrites of sensory neurons

45.3 How Do Sensory Systems Detect Mechanical Forces?

Auditory systems use hair cells to sense sound waves

            -Auditory systems use mechanoreceptors to convert pressure waves to receptor potentials

            -Human ears: pinnae collect sound waves & direct them to auditory canal

-Tympanic membrane (eardrum) covers end of auditory canal & vibrates in response to pressure waves

-Middle ear is an air filled cavity

-Open to throat via the Eustachian tube which equilibrates air pressure between middle ear and the outside

-Ossicles: malleus, incus, stapes transmit vibrations of tympanic membrane to oval window

-translate vibrations of tympanic membrane to smaller movement but greater force at the smaller oval window

-movement of oval window is translated into pressure changes in the fluid-filled inner ear

            -Inner ear includes cochlea

-Cochlea is tapered/coiled chamber composed of three parallel canals separated by two membranes: Reissner’s membrane, and basilar membrane

-organ of Corti sits on basilar membrane; transduces pressure waves into action potentials

-upper & lower canals are joined at the distal end

-Round window is flexible membrane at the end of the canal

-Pressure waves can travel all the way around to reach round window, or “shortcut” across the basilar membrane by flexing

-Different pitches flex the basilar membrane at different locations (high pitch = short distance, low pitch = long distance)

-Action potentials stimulated by mechanoreceptors at different positions along the organ of Corti are transmitted to the brain via the auditory nerve

            -Deafness

                        -Conduction deafness: loss of function of tympanic membrane or ossicles

                        -Nerve deafness: damage to inner ear/auditory nerve pathways

-Hair cells in the organ of Corti can be irreversibly & cumulatively damaged by loud sounds

Hair cells provide information about displacement

            -Hair cells: mechanoreceptors in organs of hearing and balance

                        -have microvilli called stereocilia

                        -bending of stereocilia open/close ion channels

                        -when plasma membrane is depolarized, neurotransmitters are released

            -Vertebrate organs use hair cells to detect position of body with respect to gravity

-Mammalian inner ear has three semicircular canals at angles to each other; sense position & orientation of head

            -Vestibular apparatus has two chambers that sense static position of head & acceleration

45.4 How Do Sensory Systems Detect Light?

            -Photosensitivity: sensitivity to light

            -A range of animal species (simple to complex) can sense & respond to light

            -They all use the same pigments: rhodopsins

Rhodopsins are responsible for photosensitivity

            -Rhodopsin consists of opsin (protein) and light-absorbing group 11-cis-retinal

            -Rhodopsin sits in plasma membrane of photoreceptor cell

            -11-cis-retinal absorbs photons of light and changes to isomer all-trans-retinal

-this triggers cascade of reactions involving a G protein signaling mechanism that results in the alteration of membrane potential

Image-forming eyes evolved independently in vertebrates and cephalopods

-in vertebrate eyes, retinal & opsin eventually separate (bleaching)

-a series of enzymatic reactions is required to return all-trans-retinal back to 11-cis-retinal, which recombines with opsin

            -Rod cell: one type of vertebrate photoreceptor

                        -release neurotransmitters from base of cell that synapses with a neuron

                        -outer segment is a stack of plasma membrane discs packed with rhodopsin

-When rhodopsin absorbs a photon of light, a cascade of events begins, starting with the activation of a G protein, transducin

-Transducin activates PDE (phosphodiesterase) which converts cGMP to GMP – the Na⁺ channels close, and the membrane is hyperpolarized

-Vertebrate eye structure

            -Sclera: tough connective tissue; becomes transparent cornea at front

            -Iris: pigmented; controls amount of light reaching photoreceptors

            -Pupil: opening of the iris

            -Lens: crystalline protein; focuses image by accommodation (changing shape)

            -Retina: photoreceptor layer

The vertebrate retina receives and processes visual information

            -Vertebrate photoreceptors: rods and cones

            -Cones have low sensitivity to light (color)

-humans have 3 types of cone cells with slightly different opsin molecules that absorb different wavelengths of light

            -Rods: responsible for night vision (black & white)

            -Retina has five layers of cells

                        -light must pass through all layers before captured by rhodopsin

                        -light not captured is absorbed by a layer of pigmented epithelial cells

-new disks are continuously regenerated by inner segments; distal ends of outer segments disks are being shed; pigmented epithelial cells phagocytose the shed disk

                        -each outer segment is totally renewed about every two weeks

            -Ganglion cells: layer at front of retina; axons form the optic nerve

                        -photoreceptor cells are connected to ganglion cells via bipolar cells

-changes in membrane potentials of rods/cones alter the rates at which they release neurotransmitters at their synapses with bipolar cells

-in response to the neurotransmitter, the membrane potentials of the bipolar cells change, altering the rate at which they release neurotransmitter onto ganglion cells

-rate of neurotransmitter release from bipolar cells determines the rate at which ganglion cells fire action potentials

-direct flow of information in the retina is from photoreceptor to bipolar cell to ganglion cell to brain

Chapter 46 – The Mammalian Nervous System: Structure and Higher Function

46.1 How Is the Mammalian Nervous System Organized?

            -Vertebrate nervous system consists of brain, spinal cord, peripheral nerves

            -Central nervous system (CNS) – brain, spinal cord

            -Peripheral nervous system (PNS) – cranial/spinal nerves that connect CNS to all tissues

A functional organization of the nervous system is based on flow and type of information

            -Neuron is excitable cell that communicates via an axon

            -Nerve is a bundle of axons that carries information

            -Afferent part of the PNS carries sensory information to the CNS

            -Efferent part of the PNS carries information from CNS to muscles & glands

            -Efferent pathways are divided into two divisions

                        -Voluntary division: executes conscious movements

                        -Autonomic division: controls physiological functions (involuntary)

-CNS also receives chemical information from hormones, and release neurohormones to send information to other neurons or to enter circulation

The vertebrate CNS develops from the embryonic neural tube

            -the CNS develops from the neural tube of the embryo

            -anterior part of tube develops into hindbrain, the midbrain, and the forebrain

            -rest of neural tube becomes the spinal cord; cranial and spinal nerves form

            -Hindbrain develops into the medulla, the pons, and the cerebellum

                        -medulla/pons control physiological functions such as breathing & swallowing

                        -cerebellum coordinates muscle control

            -Midbrain becomes structures that process visual & auditory information

            -hindbrain + midbrain are known together as the brain stem

            -Forebrain develops into the central diencephalon and the surrounding telencephalon

                        -Diencephalon consists of the thalamus and the hypothalamus

                                    -Thalamus: final relay station for sensory information

                                    -Hypothalamus: regulates physiological functions such as hunger/thirst

                        -Telencephalon consists of two cerebral hemispheres (cerebrum)

                        -evolutionary trend: increase size/complexity of telencephalon (telencephalization)

-in humans, telecephalon is largest brain region involved in sensory perception, learning, memory, and behavior

The spinal cord transmits and processes information

-Spinal cord conducts information between brain and organs, integrates information from PNS, and responds by issuing motor commands

            -Anatomy of spinal cord

                        -Gray matter in the center (cell bodies of spinal neurons)

                        -White matter surrounding (axons that conduct information)

                        -Spinal nerves extend from the spinal cord

                        -each spinal nerve has two roots – connecting with dorsal horn and ventral horn

                        -Afferent axons enter through dorsal root

                        -Efferent axons enter through ventral root

            -Spinal reflex: afferent information converts to efferent activity without the brain

                        -Ex: Monosynaptic knee-jerk reflex

-Stretch receptors send axon potentials through dorsal horn to ventral horn via sensory axons

-At synapses with motor neurons in the ventral horn, action potentials sent to leg muscles, causing contraction

                        -Sensory neuron synapses directly on motor neuron of the same muscle

                        -Also, inhibitory disynaptic reflex

                        -Sensory neuron synapses on inhibitory interneuron in spinal cord

                        -Interneuron inhibits motor neuron of antagonist muscle; relaxes muscle

The reticular system alerts the forebrain

            -Reticular system: network of neurons in the brain stem

            -A distinct group of neurons in the CNS is called a nucleus

            -Reticular formation activity can be high or low in the brain stem

                        -Low/mid: balance, coordination

                        -High: sleep & wakefulness known as reticular activating system

The core of the forebrain controls physiological drives, instincts, and emotions

            -Limbic system: formed by structures in primitive regions of telencephalon

                        -Amygdala: fear, fear memory

                        -Hippocampus: transfers short-term memory to long-term memory

Regions of the telencephalon interact to produce consciousness and control behavior

            -Cerebral hemispheres are dominant in mammals

            -Cerebral cortex: sheet of gray matter covering each hemisphere, convoluted to fit in skull

                        -Gyri: ridges of cortex

                        -Sulci: valleys of cortex

            -Regions have specific functions

            -Association cortex: areas that integrate or associate sensory information or memories

            -The four cortical lobes: temporal, frontal, parietal, occipital

            -Temporal lobe receives & processes auditory information

                        -Association areas involve: identification, object naming, recognition

                        -Agnosia: disorder of temporal lobe; aware of stimulus, cannot identify

            -Frontal lobe: the central sulcus divides frontal & parietal lobes

                        -Primary motor cortex: located in front of central sulcus

                        -Controls muscles in specific body areas

                        -Association areas involve: planning, personality

            -Parietal lobe:

                        -Primary somatosensory motor cortex: behind central sulcus

                        -Receives touch and pressure information

                        -Association areas involve: attending to complex stimuli

-Contralateral neglect syndrome: inability to recognize stimuli on one side of body when opposite parietal lobe is damaged

            -Occipital lobe

                        -Receives & processes visual information

-Association areas involve: making sense of visual world, translating visual experience into language

46.2 How Is Information Processed by Neuronal Networks?

The autonomic nervous system controls involuntary physiological functions

            -Autonomic nervous system (ANS) output of CNS that controls involuntary functions

            -Has two divisions that work in opposition

-Sympathetic and parasympathetic divisions distinguished by anatomy, neurotransmitters, & actions

            -Sympathetic: fight-or-flight response; preps body for emergencies

            -Parasympathetic: rest & digest; slows heart rate & lowers blood pressure

-All autonomic efferent pathways begin with cholinergic neuron that uses ACh, has cell body in brain stem or spinal cord (preganglionic neurons)

-The neuron that they synapse with is in a collection of neurons called a ganglion

-This second neuron is postganglionic because its axons leaves the ganglion & synapses with cells in the target organs

-Parasympathetic division: postganglionic neurons are mostly cholinergic

-Sympathetic division: postganglionic neurons are noradrenergic; uses norepinephrine as neurotransmitter

-Target cells receiving both inputs respond in opposite ways to acetylcholine & norepinephrine (ex. Pacemaker cells in heart)

-Anatomy of parasympathetic  sympathetic divisions

            -Parasympathetic divison: sacral region contains preganglionic neurons

            -Sympathetic division: thoracic & lumbar regions contain preganglionic neurons

Patterns of light falling on the retina are integrated by the visual cortex

            -Convergence of information in the retina

-Receptive field of photoreceptors that receive information from a small area of the visual field activates a ganglion cell

-Ganglion cell transmits information to thalamus, then to visual cortex (part of occipital lobe)

-Receptive fields have two concentric regions: center and surround

-Each receptive field can be on-center or off-center

-On-center cell: light falling on center excites ganglion cell

-Off-center cell: light falling on center inhibits ganglion cell

-Surround areas have opposite effect; ganglion activity depends on which part of field is stimulated

-Photoreceptors send information to ganglion cells via bipolar cells

-Lateral connections through horizontal cells modify communication

-Receptive field results from pattern of synapses between photoreceptors, horizontal cells, amacrine cells, and bipolar cells

-Effects of glutamate on on/off-center bipolar cells

            -On-center bipolar cells

                        -Glutamate is inhibitory, cells hyperpolarized in dark

                        -Cells depolarize in light; increase firing rates of ganglion cells

            -Off-center bipolar cells

                        -Glutamate is excitatory, cells depolarized in dark

                        -Cells hyperpolarize in light; reduces firing rate of ganglion cells

-Receptive fields of the visual cortex

            -Simple cells are stimulated by bars of light, corresponding to circular receptive fields of adjacent ganglion cells

            -Complex cells respond to light with a particular orientation, across the retina

Cortical cells receive input from both eyes

            -Binocular vision results from overlapping fields of view

            -Optic nerves from each eye join at the optic chiasm

            -Half of axons from each retina go to opposite side of the brain

            -Visual cortex organized in stripes and columns

                        -Stripes: areas across the cortex

                        -Column: areas across depth of the cortex

                        -Cells in the border of stripe or column are binocular cells

-They receive input from both eyes & measure disparity of stimulus, and where it falls on each retina

46.3 Can Higher Function Be Understood in Cellular Terms?

Sleep and dreaming are reflected in electrical patterns in the cerebral cortex

            -Electroencephalogram (EEG)

                        -measures activity of groups of neurons

                        -records changes in electrical potential between electrodes, over time

            -Electromyogram (EMG): records skeletal muscle activity

            -Electrooculogram (EOG): measures eye movement

            -Humans have two main sleep states

-Rapid-eye-movement (REM) sleep: dreams occur; brain inhibits skeletal muscle activity

            -Non-REM sleep: have four progressive stages; 3&4 are slow-wave sleep

                        -Neurons in thalamus & cerebral cortex are less responsive

                        -When awake, reticular formation is active, cells depolarize often

-At sleep onset, activity slow in reticular formation; less neurotransmitter released; cells hyperpolarize and are less excitable

                        -Cells fire in bursts during non-REM sleep

            -In transition between non-REM and REM sleep

                        -brain stem nuclei become active again

                        -firing bursts cease

                        -cortex can process information as cells return to threshold, can depolarize

                        -Sensory and motor pathways are still inhibited (hence bizarre dreams)         

Some learning and memory can be localized to specific brain areas

            -Learning is the medication of behavior by experience

            -Memory is what the nervous system retains

-Long-term potentiation (LTP) and long-term depression (LTD) describe how synapses become more or less responsive to repeated stimuli

            -both may be fundamental to learning and memory

            -Associative learning: when two unrelated stimuli become linked to a response

            -Conditioned response is an example of associative learning (Pavlov’s dog)

            -Memory: can be associated with specific brain regions, attributed to neuronal properties

                        -Immediate memory: events happening now

                        -Short-term memory: lasts 10-15 minutes

                        -Long-term memory: lasts for days, up to lifetime

            -Memories have to be transferred from short-term to long-term by hippocampus

                        -Hippocampal/limbic system damage can prevent this transfer

            -Declarative memory: people, places, things that can be recalled and described

            -Procedural memory: how to perform a motor task that cannot be described

            -Fear memory formation involves the amygdala

Language abilities are localized in the left cerebral hemisphere

            -Laterization of language functions show that 97% occur in the left hemisphere

            -Brain hemispheres connected by corpus callosum (a bundle of axons)

-Aphasia is a deficit in the ability to use or understand words; occurs after damage to left hemisphere

            -Language areas

-Broca’s area: frontal lobe; damage results in slow/lost speech; but can read and understand language

-Wernicke’s area: temporal lobe; damage results in an inability to speak sensibily; written/spoken language not understood; may still be able to produce speech

-Angular gyrus: adjacent area essential for integrating spoken & written language

            -How language is processed

                        -Spoken language:  input flow from auditory cortex to Wernicke’s area

-Written language: input flow from visual cortex to angular gyrus to Wernicke’s area

-Speech commands: formulated in Wernicke’s area, travel to Broca’s area, then to primary motor cortex for production

                        -Brain imaging shows metabolic differences in brain regions using language

Chapter 47 – Effectors: How Animals Get Things Done

47.1 How Do Muscles Contract?

            -Muscles and skeletons comprise the musculoskeletal system

            -They are effectors that produce movement

            -Types of vertebrate muscles

                        -Skeletal muscles: voluntary movement, breathing

                        -Cardiac: beating of heart

                        -Smooth muscle: involuntary, movement of internal organs

Sliding filaments cause skeletal muscle to contract

            -Skeletal muscles are striated

            -Cells are called muscle fibers with multiple nuclei

            -Formed from the fusion of embryonic myoblasts

            -One muscle consists of many muscle fibers bundled together by connective tissue

            -Contractile proteins

                        -Actin: thin filaments

                        -Myosin: thick filaments

            -Each muscle fiber has several myofibrils: bundles of actin and myosin filaments

            -Each myofibril consists of repeating units called sarcomeres, marked by Z lines

            -Sarcomere: overlapping actin and myosin filaments

            -Bundles of myosin filaments held in place by titin (largest protein in body)

            -Regions of the sarcomere

                        -Z lines: bounds each sarcomere, anchors thin actin filaments

                        -A band: contains all myosin filaments, centered in sarcomere

                        -H zone/I band: regions where actin /myosin filmanets do not overlap

-M band: region in H zone (dark stripe), contains proteins that hold myosin filaments in their regular arrangement

Actin-myosin interactions cause filaments to slide

            -Sliding filament theory of muscle contraction

                        -Depends on structure of actin and myosin molecules

                        -Myosin heads can bind specific sites on actin molecules to form cross bridges

                        -Myosin changes conformation à actin slide 5-10 nm

Actin-myosin interactions are controlled by calcium ions

-Muscle contraction initiated by action potentials from motor neuron at the neuromuscular junction

            -Motor unit: all muscle fibers activated by one motor unit

            -One muscle may have many motor units

-to increase strength of muscle contraction: increase firing rate of motor neuron or activate more motor units

            -Muscle cells are excitable

                        -plasma membrane can conduct action potentials

-Acetylcholine released by motor neuron at neuromuscular junction, opens ion channels in the motor end plate

            -Action potentials travel deep within muscle fiber via T tubules

            -T tubules (transverse tubules) descend into sarcoplasm (muscle fiber cytoplasm)

-T tubules run close to the sarcoplasmic reticulum (ER), which is closed compartment that surrounds each myofibril, and has Ca²⁺ pumps

            -At rest, there is high Ca²⁺  concentration in the sarcoplasmic reticulum

            -Action potential reaches receptor proteins, open Ca²⁺ channels

            - Ca²⁺ flow out of SR and triggers interaction of actin and myosin

            -Actin filaments contain tropomysin  and troponin

            -Troponin: has 3 subunits that bind to actin, myosin, and Ca²⁺

            -Tropomyosin: blocks binding sites on actin at rest

            -When Ca²⁺ is released, it binds to troponin, which changes conformation

            -Troponin is bound to tropomyosin – twisting of tropomyosin exposes actin binding sites

            -When Ca²⁺ pumps remove Ca²⁺ from sarcoplasm, contraction stops

Cardiac muscles causes the heart to beat

            -Cardiac muscles also striated; muscles are smaller than skeletal and have one nucleus

            -Also branch and interdigitate; can withstand high pressures

            -Gap junctions: electrical synapses pass action potential from cell to cell

            -Intercalated discs provide mechanical adhesion between cells

            -Pacemaker and conducting cells initiate and coordinate heart contractions

            -Heartbeat is myogenic – generated by heart muscle itself

                        -rate can be modified by ANS, but not necessary for function

Smooth muscle causes slow contractions of many internal organs

            -Smooth muscle in most internal organs, under ANS control

            -cells arranged in sheets; electrical contact via gap junctions

            -action potential in one cell can spread to all others in the sheet

            -Plasma membrane of smooth muscle cells sensitive to stretch

            -Stretched cells depolarize, fire action potentials which starts contraction

            -Smooth muscle contraction

                        - Ca²⁺  influx into sarcoplasm, stimulated by stretch, action potential, or hormone

                        - Ca²⁺ binds with calmodulin which activates myosin kinase

                        -myosin kinase phosphorylates myosin heads, which can bind and release actin

Single skeletal muscle twitches are summed into graded contractions

            -Twitch: minimum unit of skeletal muscle contraction

            -measured in terms of tension; single action potential generates single twitch

            -force generated depends on how many fibers are in motor unit

            -Tension generated by entire muscle depends upon:

                        -Number of motor units activated

                        -Frequency at which motor units are firing

-Single twitch: if action potentials are close together in time, twitches are summed, tension increases

-Twitches sum because Ca²⁺ pumps cannot clear Ca²⁺ from sarcoplasm before next action potential arrives

-Tetanus: when action potentials are so frequent that Ca²⁺ is always present in sarcoplasm

            -How long muscle fibers can sustain contraction depends on ATP supply

                        -ATP is needed to break myosin-actin bonds, and “re-cock” myosin heads

                        -to maintain contraction, actin-myosin bonds have to keep cycling

            -Muscle tone: a small but changing number of motor units are contracting

                        -many muscles maintain a low level of tension even when body at rest

-muscle tone constantly being adjusted by nervous system

47.2 What Determines Muscle Strength and Endurance?

Muscle fiber types determine endurance and strength

            -Fast-twitch vs slow-twitch muscle fibers

                        -differ in development of tension, fatigue, contraction, and work

            -Slow-twitch muscle fibers: oxidative or red muscle

-contain myoglobin (oxygen binding protein), many mitochondria, well-supplied with blood vessels

                        -maximum tension develops slowly, but higly resistant to fatigue

                        -contain reserves of glycogen and fat

                        -can produce ATP as long as oxygen is available

                        -muscles with high proportion of slow-twitch = good for aerobic work

            -Fast-twitch muscle fibers: glycolytic or white muscle

                        -fewer mitochondria, fewer blood vessels, little or no myoglobin

                        -develop greater maximum tension faster, but fatigue more quickly

                        -can’t replenish ATP for prolonged contraction

Exercise increases muscle strength and endurance

-Proportion of fast-twitch and slow-twitch fibers is mostly genetic, but can be altered by training to a certain extent

            -Anaerobic activities increase muscle strength

                        -new actin and myosin filaments form

                        -muscle becomes larger

            -Aerobic activities increase endurance

-oxidative capacity enhanced by increasing number of mitochondria, blood vessels, myoglobin, and enzymes

Other kinds of effectors

            -Glands: effector organs that produce and release chemicals (endocrine, exocrine)

            -some reptiles, amphibians, mollusks, and fish have poison glands

Chapter 48 – Gas Exchange in Animals

48.1 What Physical Factors Govern Respiratory Gas Exchange?

            -All cells need O₂ and need to get rid of CO₂ (waste of cellular metabolism)

            -Respiration gets O₂ in and moves CO₂ out

Diffusion is driven by concentration differences

            -Gas moves from higher to lower concentrations

Fick’s law applies to all systems of gas exchange

            -Q = DA(P₁ – P₂)/L

            -Q = rate of diffusion between two locations

            -D = diffusion constant characteristic of gas and medium

            -A = cross-sectional area of diffusion surface

            -P = partial pressure  of gas at each location

            -L = distance between two locations

            -Partial pressure gradient: large if L low or (P₁ – P₂) is high

            -To increase diffusion (Q):

                        -Increase A (surface area)

                        -Increase (P₁ – P₂), partial pressure difference

                        -Decrease L, distance

Air is a better respiratory medium than water

            -Harder to breathe in water than in air because water carries much less O₂

                        -water – 10 mL per liter, air 200 mL per liter

            -Oxygen diffuses more slowly in water than in air

            -Harder to move water across respiratory surfaces than air

High temperatures create respiratory problems for aquatic animals

            -Increase in temperature causes problems

                        -Induces increased need for oxygen in body due to higher metabolic rate

                        -However, water carries less oxygen at higher temperatures

O₂ availability decreases with altitude

            -Po₂ decreases from 159 mmHg to 80 mmHg at 5800 m altitude

CO₂ is lost by diffusion

            -high concentration of CO₂ in lung/gills diffuse to environment (low concentration)

48.2 What Adaptations Maximizes Respiratory Gas Exchange?

Respiratory organs have large surface areas

            -Gills and lungs have convoluted surfaces to increase surface area

            -Also are elastic

Transporting gases to and from the exchange surfaces optimizes partial pressure gradients

-Minimization of path length

                        -very thin respiratory membrane evolved (minimize L)

            -Maximizing difference in concentration

                        -Ventilation: blow fresh air from environmental side

                        -Perfusion: pump low-O₂ high-CO₂ blood on tissue side

                        -Metabolic sinks: carbonic anhydrase

Insects have airways throughout their bodies

            -Trachae: insect system of gas exchange

                        -highly branched series of tubes that lead throughout insect tissues

                        -no lung

                        -air enters through openings known as spiracles

                        -Fine branching until they end in tiny air capillaries

                        -distance between air and mitochondria are only a few micrometers

                        -small diameter of tubes ultimately limits diffusion, so insect must be small

Fish gills use countercurrent flow to maximize gas exchange

            -Gills: have large surface area

                        -bony gill arches for support

                        -gill filaments are fingers of gill overlapping

                        -perpendicular lamellae (ridges) on their surface

            -Water is pumped across gills by mouth closing to push water in

            -Opercular flaps open to suck water out the other end

            -unidirectional, counter-current flow maximizes gas exchange

            -Blood flows in opposite direction of water

            -Max diffusion distance with very thin epithelial cells between water and blood

Birds use unidirectional ventilation to maximize gas exchange

            -Bird lungs are smaller than mammalian lungs

            -Birds able to live at much higher altitudes and sustain very active lifestyle

            -Unidirectional ventilation of lungs and air sacs (no dead space)

            -Two breathes fill and empty the bird lung

                        -Inhale 1: fresh air to posterior air sacs

                        -Exhale 1: fresh air from posterior air sacs to lung

                        -Inhale 2: fresh air to posterior air sacs; air from lung goes to anterior air sacs

-Exhale 2: air from anterior air sacs go out trachea, fresh air from posterior air sacs to lung

            -Unidirectional, continuous ventilation of lung

Tidal ventilation produces dead space that limits gas exchange efficiency

            -Mammalian lungs work by tidal breathing

                        -Severely limits concentration difference of oxygen between air and blood in lung

                        -fresh air moves into lung only half of the time

                        -concentratino of oxygen in lung much less in air (500 mL fresh + 2000 mL stale)

                        -bidirectional flow eliminates possibility for countercurrent exchange

            -Adaptation to overcome limitations

                        -Enormous surface area (badminton court size in human)

                        -short path to diffusin (2 μm) across very thin alveolar cells

                        -surfactant and mucous lowers surface tension and makes breathing less costly

48.4 How Does Blood Transport Respiratory Gases?

Hemoglobin combines reversibly with oxygen

            -Blood plasma has low oxygen-carrying capacity; unable to support basal metabolism

            -thus, the evolution of oxygen-carrying molecules

            -Hemoglobin increases oxygen carrying capacity 60x

                        -4 polypeptide units and iron

                        -reversibly binds oxygen

                        -ability to bind oxygen depends on Po₂ (partial pressure of oxygen in environment)

            -Hemoglobin picks up oxygen at high Po₂ in lung; releases oxygen at low Po₂ in tissues

            -Sigmoid curve of oxygen saturation

                        -normal deoxygenated blood is at top of steep part of curve

                        -small drop in Po₂ = large loss of oxygen from hemoglobin

                        -rapid response with large capacity

            -most hemoglobin molecules drop only 1 of the 4 oxygens in circuit through the body

                        -when tissues need extra oxygen, hemoglobin still has 3 more oxygens

Myoglobin holds an oxygen reserve

            -Myoglobin is muscle protein that binds oxygen; also contains iron

            -higher affinity for oxygen than hemoglobin

                        -can pick up oxygen at tissue levels of Po₂ where hemoglobin releases oxygen

-provides reserve of oxygen for muscle cells when metabolic level is high and blood flow interrupted due to muscle contraction

            -more myoglobin in muscles that are active all the time

The affinity of hemoglobin for oxygen is variable

            -Hemoglobin affinity of oxygen varies between species

            -Human fetus hemoglobin has higher affinity for oxygen compared to maternal hemoglobin

                        -fetal blood can tae oxygen from maternal blood

            -Llamas live at high altitude

                        -llama hemoglobin must have higher affinity for oxygen than animals at sea level

                        -tissues must operate at lower O₂

            -Both human fetus and llama have oxygen binding curves to left of adult human

            -Hemoglobin affinity also affected by pH

                        -low pH shifts oxygen binding curve to right; decreases affinity for oxygen

-when metabolism is high, lactic acid is made from anaerobic fermentation + fatty acids and CO₂ which forms carbonic acid

-decreased binding = hemoglobin releases more oxygen in highly active tissues that needs it

Carbon dioxide is transported as bicarbonate ions in blood

            -Conversion of CO₂ to bicarbonate catalyzed by carbonic anhydrase in RBC

            -in tissue plasma, enzyme pulls CO₂ out of solution quickly

-maximizes concentration difference between plasma and tissue à maximize CO₂ diffusion into plasma

-In lung, reaction is reversed

            -CO₂ lost to air, carbonic anhydrase catalyzes converseion of bicarbonate to CO₂

            -Carbonic anhydrase acts as CO₂ source; helps maintain high partial pressure gradient

48.5 How is Breathing Regulated?

Breathing is controlled in the brain stem

-Need for oxygen is different for each activity

            -must be coordinated with eating and speaking

            -neurons in brain stem generate rhythm for inspiration; respond to regulatory factors

Regulating breathing requires feedback information

            -Rhythm is not sensitive to O₂

-high capacity of hemoglobin for O₂ à relative insensitivity, since they usually do not change much

            -Rhythm is highly sensitive to CO₂

-Ex: if breathing from small reservoir, breathing increases in attempt to drive off CO₂, even when level of O₂ is constant in reservoir

                        -major site of CO₂ sensitivity is on ventral surface of medulla

            -Sensitivity to O₂ in aorta and carotid arteries, called aortic and carotid bodies

Chapter 49 – Circulatory Systems

49.1 Why Do Animals Need a Circulatory System?

            -Function of the circulatory system

                        -transport of gases, nutrients, and wastes in and out, between tissue/environment

Some animals do not have circulatory systems

            -simple animals do not need circulatory system

            -body cells are close to environment

                        -gastrovascular cavity in hydra, animal is 2 cells thick, flat body shape

                        -simple diffusion is enough

Open circulatory systems move extracellular fluid

-Open circulatory system: interstitial fluids squeezed through intracellular spaces as animal moves, sometimes assisted by muscular pump (heart)

            -Can have blood vessels, but no true distinction between blood & interstitial fluid

            -Disadvantages: low pressure, slow flow, not adaptive for high metabolic rate

Closed circulatory system circulates blood through a system of blood vessels

            -Closed circulatory system: some components of blood never leaves system

            -Advantages:

                        -blood moves faster when volume of passage is controlled

                        -faster exchange of gas/nutrients

-distribution of blood to specific tissue is controllable (gates, valves), finer regulation

                        -larger blood elements kept inside system, become specialized for transport (RBC)

49.2 How Have Vertebrate Circulatory Systems Evolved?

            -Vertebrate heart: general evolutionary trend

-Progressively more separation of blood that goes to gas exchange organs and blood that goes to body

                        -Fish: heart à gills à body à heart

                        -Mammals: pulmonary and systemic circuits

            -Mammalian/Avian circulatory system

                        -Heart à arteries à arterioles à capillaries à venules à veins à heart

                        -Right heart pumps blood between heart and lung

                        -Left heart pumps blood between heart and body

                        -Four chambers: two atria, two ventricles

                        -No mixture of blood between pulmonary and systemic parts of circulation

Fish have two-chambered hearts

            -Fish hearts have two chambers: atrium and ventricle

            -Ventricle pumps blood to gills, then to aorta to body

-Most of pressure in heart is dissipated in the gill capillary bed (large increase in volume, small vessels), pressure in body is low so limited rate of supply of gas/nutrients

-Lungfish: critical improvements

-Lungfish exposed to water with low oxygen; swallow air when water does not have enough oxygen

-Outpocketing of gut serves as primitive lung with adaptations for gas exchange (high surface area, thin walls)

-Important evolutionary branch allow air breathing for first time à eventual evolution of terrestrial vertebrates

-Some gill arches deliver blood directly to lung and new vessel taking blood back to heart, which is the first evolved pulmonary circulation

-Some gill arches retain capillaries, so gill breathing is retained

-First development of direct circuit from heart to body (some gill arches lose capillaries and shunt blood directly to body)

-Separation of pulmonary and systemic circuits

Amphibians have three-chambered hearts

            -Amphibians are the first complete lung breather

            -Amphibian heart has three chambers: two atria and one ventricle

-Advantage of partially separate pulmonary circulation in which heart pumps oxygenated blood directly to body under high pressure

-Problem: potential mixing of oxygenated/deoxygenated blood in atrium, decreased by channels in the frog heart

Birds and mammals have fully separated pulmonary and systemic circuits

            -Mammal/Avian hearts have four chambers: two atria, two ventricles

            -Oxygenated blood pumped to body under high pressure (rapid transport)

-No mixing of oxygenated blood from lungs with deoxygenated blood from body; both have separate atria

-Deoxygenated blood from body is unmixed when pumped to lung, maximize gas exchange in lung because blood is uniformly low in oxygen

            -Can maintain different pressures in two circulations; higher in systemic circuit

49.3 How Does the Mammalian Heart Function?

Blood flows from right heart to lungs to left heart to body

            -Right heart = pulmonary circuit, left heart = systemic circuit

            -Valves prevent the backflow of blood

-Atrioventricular valves lie between atria and ventricle; prevent backflow when ventricles contract

-Pulmonary valve/aortic valve lie between ventricles and arteries, and prevent backflow when ventricles relax

            -Right atrium receives deoxygenated blood from body through large veins

                        -Superior vena cava: blood from upper body

                        -Inferior vena cava: blood from lower body

            -Blood passes from right atrium through an AV valve into right ventricle

-Right atrium contracts, right ventricle contracts causing AV valve to shut, and blood is pumped through the pulmonary artery to the lungs

            -Blood returns to left atrium through the pulmonary vein

            -Left ventricle fills as blood enters through AV valve

-Left atrium contracts, left ventricle contracts, AV valve closes and the aortic valve opens, and blood circulates through the aorta

-In cardiac cycle: both sides of heart contract at same time (atria then ventricle)

            -Systole: when ventricles contract

            -Diastole: when ventricles relax

The heartbeat originates in the cardiac muscle

            -Properties of cardiac muscle

                        -Gap junctions between fibers allow rapid spread of depolarization and contraction

                        -Mesh of fibers

-Specialized pacemaker cells; unstable membrane potential; depolarize without external influence from nervous system: myogenic origin of action potential

                        -nervous system/hormones influence rate of firing

            -Cardiac muscles function as pump

                        -Cells are in electrical contact with each other through gap junctions

                        -Spread of action potentials stimulate contraction in unison

                        -Pacemaker cells can initiate action potentials w/o input from nervous system

            -Sinoatrial node: location of the primary pacemaker cells (superior vena cava and atrium)

-Resting membrane potential is less negative, not stable so cells gradually reach threshold

                        -Action potentials are broader and slower to return to resting potential

A conduction system coordinates the contraction of heart muscle

            -One cell in sinoatrial node depolarizes to start cardiac cycle

            -Action potentials spread to atria first à contract in unison

-No gap junctions between atria and ventricles, so action potential does not spread to ventricles

            -Action potential in atria stimulates the atrioventricular node

-Node consists of non-contracting cells that send action potentials to the ventricles via the bundle of His

            -bundle of His divides into left/right bundle branches that run to the tip of the ventricles

            -From the ventricle tips, Purkinje fibers spread throughout the ventricles

            -contraction spreads rapidly and evenly through the ventricles

            -Delay between contraction of atria and ventricles ensures proper blood flow

Electrical properties of ventricular muscles sustain heart contraction

            -Neural control of heart beat

            -Sympathetic innervation of sinoatrial/atrioventricular nodes

                        -Neurotransmitter is norepinephrine

                        -Speeds contraction

            -Parasympathetic innervation of sinoatrial node

                        -Neurotransmitter is acetylcholine

                        -Slows contraction

            -Nervous system controls heart rate by influencing resting potential

                        -Norepinephrine (sympathetic) increases permeability of Na⁺/K⁺ and Ca²⁺ channels

                        -Resting potential rises more quickly; action potentials closer together

-Acetylcholine (parasympathetic) increase permeability of K⁺, decreases that of Ca²⁺ channels

                        -Resting potential rises more slowly; action potentials farther apart

49.4 What Are the Properties of Blood and Blood Vessels?

Red blood cells transport respiratory gases

            -Erythrocytes generated from stem cells in bone marrow

            -Proliferation triggered by erythropoietin (released by kidney in response to low oxygen)

            -No nucleus, ER, or mitochondria – essentially “bag” of hemoglobin and some enzymes

Platelets are essential for blood clotting

            -Platelets are pieces of large cells in bone marrow with clotting factors

Blood circulates throughout the body in a system of blood vessels

            -Vascular system: 60,000 miles, 2.5x Earth’s circumference

-Arteries: thick to withstand pressure; elasticity reduces resistance to blood flow (easier to pump blood)

                        -Energy of heart beat stored in elastic expansion of arteries

                        -slowly released between heart beats = smoother blood flow

                        -Arterioles = smaller arteries; highly branched and reduced pressure

                        -Atherosclerosis: hardening of arteries; puts strain on heart

Materials are exchanged in capillary beds by filtration, osmosis, and diffusion

-Capillary bed: very large volume, therefore big pressure drop/reduced flow rate as blood enters capillary bed

-Thin, permeable walls to allow exchange of gases and nutrients with cells that line capillaries

            -Capillary walls are single layer of endothelial cells; tiny holes called fenestrations

            -Permeable to water, ions, small molecules, but not large proteins

            -Two opposite pressures

-Hydrostatic pressure from heart beat causes water to leave capillaries (large molecules and cells stay behind)

-Reverse osmotic pressure: loss of water from blood increases concentration of solutes in blood relative to interstitial fluid; creates reverse osmotic pressure to move water back in

                        -More water squeezed out on arterial side (high hydrostatic pressure); net flow out

                        -More osmotic pressure on venous side; net flow in

            -Permeability of capillary beds in different tissues

                        -Digestive tract: high permeability, large food molecules pass between gut/blood

                        -Most tissues: free passage of CO₂, glucose, lactate, Na⁺, Cl^-

-Brain: walls have tight junctions of high resistance; blood-brain barrier protects brain from rapid ionic exchanges of blood

Blood flows back to the heart through veins

-Veins: return blood to heart

                        -can expand more than arteries, blood collects

                        -have valves that prevent back flow

                        -low pressure; blood return to heart aided by skeletal muscle contractions

Lymphatic vessels return interstitial fluid to the blood

-Lympatic system returns interstitial fluids to blood via the thoracic duct that empties into large veins at base of neck

49.5 How Is the Circulatory System Controlled and Regulated?

Autoregulation matches local blood flow to local need

            -Low oxygen and high CO₂ relaxes smooth muscles

            -Precapillary sphincters relax and increase blood flow to area

Arterial pressure is controlled and regulated by hormonal and neuronal mechanisms

            -Sympathetic neural control

-Control of smooth muscle in most organs (norepinephrine) causes contraction of smooth muscles around capillaries, reduce blood flow

                        -Fight-or-flight response increases blood flow to muscles

-Sympathetic innervation of skeletal muscles (acetylcholine) relaxes smooth muscles; better blood flow

            -Parasympathetic neural control

                        -Acetylcholine innervation of heart; slows heart rate

            -Endocrine control

-Epinephrine increases blood pressure by acting on sinoatrial node to increase heart rate

-Kidney control body fluids with angiotensin which increases when blood pressure falls, cause arterioles to constrict

-Vasopressin from posterior pituitary constricts small peripheral vessels, increase blood pressure, increase flow to essential organs

            -Autonomic control stimuli

                        -Stretch receptors in aorta/carotid activated when blood volume increases

-inhibition of sympathetic system to relax smooth muscles to reduce pressure and stretch of receptors, and reduce heart rate

-Reduction on arterial pressure causes hypothalamus to release vasopressin, which acts on smooth muscles to make them constrict, and also increase kidney water retention

-Emotion: input from brain areas regulate circulation

-Carotid bodies: sensitive to oxygen

Chapter 18 – Immunology: Gene Expression and Natural Defense Systems

18.1 What Are the Major Defense Systems of Animals?

            -Nonspecific defenses: innate, inherited mechanisms that protect the body

            -Specific defenses: adaptive mechanisms aimed at a specific pathogen

Blood and lymph tissues play important roles in defense systems

            -Blood contains plasma, erythrocytes, leukocytes, and platelets

                        -Erythrocytes (RBC): 5 billion/mL

                        -Leukocytes (WBC): 7 million/mL

            -Leukocytes are further divided

                        -Lymphocytes: B cells and T cells

                        -Phagocytes: engulf nonself and digest; ex. Macrophages

            -Lymph: fluid derived from blood

                        -Accumulates in between cells (interstitial space)       

                        -Moves outside the closed circulatory system in the slower lymphatic system

                        -Returned to blood via the thoracic duct

                        -Lymph nodes filter fluid; WBC mature in lymph nodes

White blood cells play many defensive roles

            -Phagocytes: engulf/digest nonself materials

                        -Macrophages present digested non-self materials to T cells

            -Lymphocytes: specific defenses

                        -T cells: born in bone marrow, mature in thymus

                        -B cells: born in bone marrow, circulate in blood and lymph

Immune system proteins bind pathogens or signal other cells

-Antibodies: soluble recognizers; proteins that bind specifically to certain substances identified by the immune system; secreted by B cells

-T cell receptors: integral membrane proteins on surface of T cells; recognize and bind to nonself substances on other cells

-Major Histocompatibility Complex: protrude from surfaces of most cells in the mammalian body; important self-identifying labels; play major parts in coordinating interactions between lymphocytes and macrophages

            -Cytokines (interleukins): signaling proteins for intercellular communication, activation

18.2 What Are the Characteristics of the Nonspecific Defenses?

Barriers and local agents defend the body against invaders

            -Skin barrier

            -Mucus: contains lysozyme that attacks cell walls of bacteria

            -Gastric juices: stomach acid contains HCl

Other nonspecific defenses include specialized proteins and cellular processes

            -Complement proteins: punch holes in foreign cell membranes, causing them to lyse

            -Interferons: anti-viral

            -Phagocytes: engulf and digest bacteria

            -Natural killer cells: attack self-cells that have gone awry (cancer, virus-infected)

Inflammation is a coordinated response to infection or injury

            -Inflammation: deals with tissue injury, surface of body or internal

            -Damaged mast cells release histamine, which induces: