PVT I Lecture 1: Introduction to Physiology PDF

PVT I Lecture 1 Introduction to physiology Dr. Todd McWhorter Suggested Reading: Colville & Bassert chapter 1 LEARNING OBJECTIVES 1. Describe the properties of animals that are of overriding physiological/functional importance. 2. Explore t...

PVT I Lecture 1 Introduction to physiology Dr. Todd McWhorter Suggested Reading: Colville & Bassert chapter 1 LEARNING OBJECTIVES 1. Describe the properties of animals that are of overriding physiological/functional importance. 2. Explore the concept of homeostasis, and its importance in physiology. 3. Develop a basic understanding of scaling & allometry (i.e. the importance of animal size).  Contact Information Dr. Todd McWhorter Eastick 1.11 (upstairs) 8313 7896 [email protected] Contact details for all course staff are on MyUni- your source for course materials! What is physiology?  What is physiology? Physiology = how animals work One of the principal disciplines for understanding health & disease. Physiology is INTEGRATIVE- physiologists study all levels of organization of the animal body. THIS COURSE: is comparative, and will emphasize the physiological mechanisms and systems you will encounter as vet techs...  EVOLUTION (& BREEDING) What is physiology? CHEMISTRY & PHYSICS ECOLOGY & BEHAVIOUR  Animals Some properties that are of overriding importance: 1) Animals are structurally dynamic 2) Animals are organized systems that require energy to maintain their organization 3) Both time and body size are fundamentally important  Animals ORGANIZATION is the structural property of an animal that persists through time (individual molecules are constantly turning over- insight from isotopes). Most cells are exposed to the internal environment, not the external one. – HOMEOSTASIS (internal constancy of body temperature, fluid volume, electrolyte concentrations, pH, blood glucose, etc.) is fundamentally important in physiology. – Allows proteins (i.e. enzymes in biochemical pathways, transporters, etc.) to operate under optimal conditions  Homeostasis “Constancy of the internal environment is the condition for free life” Most cells in an (endothermic) vertebrate animal’s body experience relative constancy of temperature, oxygen, osmotic pressure, pH & salt concentrations... Claude Bernard BECAUSE PHYSIOLOGICAL MECHANISMS French physiologist/physician REGULATE THESE PROPERTIES. (1813-1878) (early insight on blood glucose homeostasis- observed liver’s role in regulation)  Homeostasis Walter B. Cannon Lawrence J. Henderson (coined the term) (counterexamples) Stable measurable pH buffering in parameters imply blood: interactions presence of of components alone (homeostatic) confer stability mechanisms to without need for ensure this stability complex regulatory mechanism(s) Nature 420, 246-251 (14 Nov 2002) doi:10.1038/nature01260  Homeostasis Regulation of blood glucose levels is an important example. – Diabetes = dysfunction of homeostatic mechanisms – Endocrine system regulates (insulin-glucagon axis)- more on this in endocrinology lectures & practicals. “Negative feedback” system (opposes deviations from set point)  Homeostasis Regulation of body temperature is another important example. Some animals thermo- conform (e.g. most fish & invertebrates). Most that we’ll deal with thermoregulate! (Osmotic concentration in blood plasma is another important example...coming in Lecture 2)  Homeostasis Physiology changes over three time frames in response to the external environment: 1) Acute – rapid, short-term, reversible responses in individual animals 2) Chronic (acclimation & acclimatization)- longer term, reversible changes in individual animals in response to environment (alteration of gene expression) 3) Evolutionary/breeding- changes within populations over generations (alteration of gene frequency & expression; epigenetics)  Homeostasis Physiology changes over three time frames in response to the external environment (example of two of those time frames here...) 24 fit male subjects, not accustomed to exercising in heat. Endurance tested in hot, dry air (49 °C, 20% RH). -Measured physiological capacity for moderate work -example of ACCLIMATION (thermoregulation, sweat gland function, etc) (phenotypic plasticity)  Homeostasis Physiology also changes based on internal programming 1) Developmental- changes that occur as an animal develops, grows & senesces. 2) Periodic- changes occurring in repeating patterns (e.g. each day or year) under control of internal biological clocks.  Homeostasis Physiology also changes based on internal programming (Haemoglobin-oxygen affinity in a foetus must be higher than it’s mother’s). Hormonal changes at reproductive maturity (e.g. puberty in humans) is another example.  Homeostasis Physiology also changes based on internal programming Annual bird migrations entail many physiological changes- these occur annually based on changes in day length (i.e. circannual). Birds increase appetite to put on fat for migration: stored energy (fat) level set point adjusted. Pre-hibernation fattening in mammals is another example...  The importance of size The study of the relation of anatomical structures and physiological parameters and time frames with body size is known as scaling, or allometry.  The importance of size Gestation time increases with body size in terrestrial mammals.  The importance of size Metabolic rate is a classic example...the “mouse to elephant curve”. Metabolic rate (watt) Body mass (kg)  The importance of size Mass-specific metabolic rate, however, scales oppositely... Elephant is WAY out there... (i.e. the motor is running faster in smaller endotherms)  The importance of size WHY? The meadow vole must eat ~6x its body mass in food per day, whereas the rhino eats only ~1/3x.  PVT I Lecture 2- Biophysics, diffusion & osmosis Dr. Todd McWhorter Suggested Reading: Colville & Bassert- chapter 2 & chapter 4 (pgs. 72-78) LEARNING OBJECTIVES 1. Describe diffusion and the chemical/physical forces that determine rate of diffusion. 2. Explore the concept of osmotic pressure: what it means, how it creates a driving force for water movement. 3. Describe osmosis and why it is important in physiology. 4. Recognise and correctly apply terminology related to osmosis and measurement of osmotic pressure.  Animals must obey the laws of chemistry & physics (and often take advantage of them) – Semi-permeable cell membranes (with protein channels & transporters) separate compartments and are crucial for maintaining homeostasis. TODAY: -Passive solute transport by simple diffusion -Osmotic pressure -Osmosis  Biophysics Biophysics is an interdisciplinary science that employs and develops approaches and methods of the physical sciences for the investigation of biological systems. – Cell membrane selectivity – Enzyme kinetics – Protein channel biology – Thermoregulation/heat transfer – Fluid dynamics (For our purposes, this means understanding how animals deal with the physical properties of molecules and energy to maintain homeostasis: -water & salt balance, energy balance, body temperature, etc.)  Equilibrium: the state towards which an isolated system moves with no inputs or outputs of energy or matter. Passive processes can only move towards equilibrium Active (energy-requiring) mechanisms can move away from equilibrium- more on this later...  Simple solute diffusion Random motion lines some molecules up with pores. Glucose moves from high to low concentration just based on the likelihood of this happening.  Simple diffusion Universal property: – Gases diffuse in air (evaporation is a special case) – Water diffuses (called osmosis) – Solutes diffuse in solutions (glucose example) – Heat diffuses ***ALL OF THESE TYPES OF DIFFUSION FOLLOW SIMILAR PRINCIPLES***  Simple diffusion Electrical gradients often influence diffusion of charged solutes at membranes. Not important in bulk solutions (electrically neutral). May play a large role in diffusion along or across cell membranes or epithelia -cell membranes often maintain separation of oppositely charged ions (i.e. act as capacitors)  Simple diffusion Biological aspects: some solutes dissolve in membranes, others require channels. – Lipid-soluble substances (e.g. steroid hormones, fatty acids) dissolve through cell membranes readily – Inorganic ions are hydrophyllic (“water loving”)- diffusion through phospholipid cell membranes is exceedingly low (without a channel or transporter…) Hydrophyllic?  Simple diffusion Hydrophyllic substances usually require channels or transporters to move across membranes (more on this later...). Electrical & concentration gradients act simultaneously to determine diffusion (given free passage across membrane) -These forces can act in the same or opposite directions.  Diffusion of ions across (cell) membranes is determined by simultaneous concentration and electrical effects Diffusion is faster when both gradients are in the same direction... Systems tend towards electrochemical equilibrium.  Living creatures are non-equilibrium systems (i.e. diffusion creates problems... but also opportunities!) Electrochemical view of a typical animal cell Electrical difference across the membrane. This simple diagram ignores the proteins (e.g. Na+-K+ ATPase, K+ leak channels) and energy (heaps!) required to achieve these gradients. Size of symbols is proportional to concentration  Concentration gradients can create electrical gradients that alter concentration gradients... Only K+ can cross this membrane At equilibrium, positive charge At the start the on the right membrane is prevents further uncharged (zeros). Diffusion of K+ from left to movement of K+. right builds up positive charges on the right side.  Osmotic Pressure A colligative property of an aqueous solution depends purely on the number of dissolved entities per unit volume. – Does not depend on chemical nature of solutes – Osmotic pressure: will a given solution gain or lose water by osmosis? Chemical properties differ Colligative properties identical  Osmotic Pressure A colligative property of an aqueous solution depends purely on the number of dissolved entities per unit volume. – Does not depend on chemical nature of solutes – Osmotic pressure: will a given solution gain or lose water by osmosis? Another example: boiling point  Osmotic Pressure A colligative property of an aqueous solution depends purely on the number of dissolved entities per unit volume. – Does not depend on chemical nature of solutes – Osmotic pressure: will a given solution gain or lose water by osmosis? Another example: freezing point Seawater freezes @ ~-2 °C  Osmotic Pressure Physiologists express this in osmolar units: 1 osmolar (Osm) = solution behaves as if it has 1 Avogadro’s number of “entities” per litre. (Avogadro's number = 6.022 × 1023) Essentially molar concentration, but depends on type of solute: 500 mM D-glucose ≈ 500 mOsm 500 mM NaCl ≈ 1000 mOsm (because the salt dissociates in solution)  Osmotic Pressure Predicting the direction of osmosis: Colour intensity α concentration Blue arrow = net osmosis (difference in osmotic pressure)  Osmosis Passive transport of water across a membrane (i.e. cell membrane, epithelium, artificial membrane) – “diffusion of water” – Water always moves FROM the solution with lower osmotic pressure, TO the one with higher osmotic pressure. – (don’t confuse with ‘water potential’, which takes into account osmosis, gravity, mechanical forces and matrix forces like capillary action- water moves toward lower potential) Higher osmotic pressure Lower osmotic pressure  Osmosis Example: osmotic uptake of water across the gills of freshwater fish -saltwater fish have the opposite problem! Seawater is ~1000 mOsm -some fish (e.g. salmonids) switch between fresh & salt water. Concentration of ions [Na+] = 160 mM [K+] = 5 [Ca2+] = 6 Concentration of ions [Cl-] = 120 [Na+] = 0.5 mM [K+] = 0.1 [Ca2+] = 0.2 [Cl-] = 0.3  Osmosis Water usually moves across membranes via channels. Cell Aquaporin membrane (AQP) water channel in cross section Water passing through pore But it can (very slowly) diffuse through the lipid bilayers of cell membranes (not physiologically significant!).  Osmosis Terminology (relative terms): – Isosmotic = same osmotic pressure – Hyposmotic = lower osmotic pressure – Hyperosmotic = higher osmotic pressure In comparative animal physiology, we usually use the normal osmolarity of animal body fluids as the point of reference Mammals: ~300 mOsm Birds: ~350 Marine fish: ~400 Freshwater fish: ~300 Seawater: 1000 Fresh water 0-15  Osmosis Terminology (relative terms): – Isosmotic = same osmotic pressure – Hyposmotic = lower osmotic pressure – Hyperosmotic = higher osmotic pressure In comparative animal physiology, we usually use the normal osmolarity of animal body fluids as the point of reference (Isosmotic for a mammal ≠ isosmotic for a bird)  Osmosis and solute physiology often interact... Example: high concentration of proteins (albumins, prealbumins, etc.) in blood plasma increases osmotic pressure. – Water tends to be drawn from interstitial space into blood. – However, blood pressure (hydrostatic) counteracts this, and tends to push water out of blood (ultrafiltration) – Net effect: blood loses water = fluid bathing cells with O2, glucose, etc. (filtration in kidneys is a special case) Active solute transport provides a means to control passive water movement... Animals generally don’t have active mechanisms to move water They can certainly move solutes though! (more on that soon...) “Water follows salt”- movement of solutes can be used to drive water.  PVT I Lecture 3- Plasma membranes, proteins, enzymes & receptors Dr. Todd McWhorter Suggested Reading: Colville & Bassert- chapter 4 (from pg. 79) LEARNING OBJECTIVES 1. Describe the important properties of enzymes, including kinetics of reactions and substrate affinity. 2. Illustrate the concept of regulation of enzyme activity, and how that relates to regulation of cell function. 3. Describe the basic properties of carrier-mediated transport of solutes across cell membranes & epithelia. 4. Describe the basic mechanisms of cell signalling, including signal reception, transduction, and the importance of amplification. Example of venoms & poisons (something you are likely to see in veterinary practice): –Higher functions of animals & homeostasis DEPEND ON ORGANISATION (CELL MEMBRANES, ENZYME FUNCTION, CELL SIGNALLING, ETC.) –Poisons & venoms often disrupt these things! -Cone snail & puff adder are both sit & wait predators- depend on molecular weapons to capture fast-moving prey  Cell membranes & intracellular membranes -Cell (plasma) membranes are composed of a lipid bilayer in which various protein molecules are embedded -Contents of cell separated from its environment -Proteins (both membrane-associated & cytoplasmic) confer function Interaction with the extracellular environment, e.g. binding extracellular proteins, cell-recognition sites. (i.e. plasma membrane) Not within bilayer, Channels, e.g. help anchor transporters, etc. cytoskeleton These two amphibians have different jumping abilities- why? These species have different LEVELS of the enzyme lactate dehydrogenase (makes ATP anaerobically). -”levels” refers to the expression of the enzyme protein Terminology: “ase” after the name of a substrate = enzyme catalyses some reaction with that substrate  Enzyme fundamentals What do enzymes do? For most biochemical reactions, this energy is exceedingly high Enzymes lower the energy of activation... (accelerate reactions) AND regulate reactions Catalyst = molecule that accelerates a reaction without being altered itself  Enzyme fundamentals Simplified reaction: E+S E-S complex E-P complex E+P Non-covalent bonds hold enzymes & substrates together Enzyme can then alter the “readiness” of the substrate to react (altering covalent bonds) Most biochemical reactions do not take place spontaneously at significant rates under physiological conditions  Enzyme fundamentals Substrate Product (produced from glucose by glycolysis) Net addition of 2x H: Enzyme modification of covalent bonds Reversible  Enzyme-catalyzed reactions exhibit hyperbolic or sigmoid kinetics Reaction velocity increases from 1 to 2 because more enzyme molecules are being used Reaction velocity cannot increase more at 3 because all enzyme molecules are being used Terminology: Vmax = maximum reaction velocity Enzyme-substrate affinity affects reaction velocity across substrate concentrations... Note Vmax is the same in all cases But reaction velocity is different for same substrate concentration (High substrate affinity) Enzyme-substrate affinity affects reaction velocity across substrate concentrations... Km = Michaelis or half-saturation constant i.e. substrate concentration at which reaction velocity is ½ max Km and enzyme-substrate affinity are inversely related... High affinity = low Km Low affinity = high Km  Modulation of existing enzymes permits rapid regulation of cell function... Rate limiting & branch point reactions are important points of modulation Modulate this and you control the entire pathway Modulate these and you control the ratio of products produced  Allosteric modulation of existing enzymes Common (but not universal) mechanism of regulation Enzyme has a binding site (allosteric or regulatory site) Modulators induce changes that influence structure Enzyme activity can be upregulated or downregulated by a modulator  Covalent modulation of existing enzymes Second important mechanism of regulation: – Modifies catalytic activity by changing covalent bonds – Requires the action of enzymes – e.g. Protein kinases & phosphatases: add or subtract phosphates; specific to specific enzymes (not general- that would be chaos) – Often act in multiple-enzyme sequences to carry out control functions Protein kinases often function in multi-enzyme sequences that bring about amplifying effects... Amplification- each newly activated kinase activates several more.  Where does transport occur? (Better question: where doesn’t it?) The non-equilibrium state of animals means that it pretty much must occur in all tissue types all the time...  “Active” transport Animals transport many solutes across cell membranes & epithelia in directions away from electrochemical equilibrium. i.e. “uphill transport” Stomach acid secretion was one of the first recognized examples: cells with an internal pH of Takes heaps of energy (ATP) ~7 secrete a fluid with a pH < 1!  Firearms “mishap” resulted in a gastric fistula (joining of stomach cavity to exterior of body) Beaumont was able to sample gastric fluids, put in fabric bags of food to test digestion, etc. Stomach acid secretion by parietal cells: H+/K+-ATPase exchanges ions- example of primary active transport... Alexis St. Martin  Basic properties of active transport mechanisms Example: proton secretion by parietal cells in stomach Energy may be drawn directly or indirectly from a process that uses ATP Primary active transport- draws energy directly from hydrolysis of ATP (i.e. transporter is an ATPase) Secondary active transport- draws energy from an electrochemical gradient of a solute (e.g. made by the Na+-K+ ATPase) Proton pump in parietal cells in the stomach is an example of a direct mechanism (i.e. 1° active transport) Recognition of active transport completes the picture for our imaginary simplified animal cell: Here’s the Na+-K+ ATPase mentioned earlier: The non-equilibrium 3x Na+ out and 2x K+ in for each pumping state of an imaginary cycle = electrogenic transport process typical animal cell. Secondary active transport of glucose in more detail... Here’s that Na+-K+ ATPase generating the electrochemical gradient... Secondary active transport of glucose in more detail... Imagine there’s a Na+- driven pinwheel in the apical membrane. Na+ turns the pinwheel (i.e. does physiological work) as it moves down its electrochemical gradient. Secondary active transport of glucose in more detail... In a real cell, there’s a protein (SGLT1) that uses the Na+ gradient to do the work of pushing glucose into the cell up its concentration gradient. Note relative font sizes Glu used to indicate relative concentration  Cell signalling: reception & transduction Signal reception: mechanism to detect the signal Signal transduction: mechanism by which intracellular activities are modified in response to extracellular signals.  Extracellular signals initiate their effects by binding to receptor proteins (4 types)... 1) Ligand-gated channels Binding of ligand causes a conformational change in the protein. Both a receptor and a channel- will typically open to permit inorganic ions to pass through (& thus alter electrical charge across the cell membrane) e.g. transmission of nerve impulses across synapses and neuromuscular junctions.  Some venoms work by blocking this mechanism... Snail lures fish with proboscis that looks like food... Snail spears fish with harpoon & injects toxins. Fish becomes paralysed. Some poisons work by blocking this mechanism... (Acetylcholine receptor antagonist)  Extracellular signals initiate their effects by binding to receptor proteins (4 types)... 2) G protein-coupled receptors Binding of ligand causes receptor to interact with G protein, which then interacts with an enzyme This activates SPECIFIC intracellular enzyme catalytic sites. Catalytic activity produces cyclic AMP or another second messenger inside the cell. e.g. cellular responses to hormones- action of epinephrine (adrenaline) on liver cells. (generally no passage of any molecule through cell membrane)  Extracellular signals initiate their effects by binding to receptor proteins (4 types)... 3) Enzyme/enzyme-linked receptors Binding of ligand activates a catalytic site on the SAME MOLECULE. Catalytic activity produces cyclic AMP or another second messenger inside the cell. e.g. cellular responses to hormones- action of atrial natriuretic peptide (ANP) in kidney to increase Na+ excretion. (generally no passage of any molecule through cell membrane)  Extracellular signals initiate their effects by binding to receptor proteins (4 types)... 4) Intracellular receptor Ligand (e.g. steroid hormone) dissolves in & diffuses through cell membrane. Ligand binds intracellular receptor. Activated ligand-receptor complex acts as a transcription factor inside the nucleus. e.g. steroid hormones, thyroid hormones, vitamin D (the only type not localized on the cell surface)