BI 315 Reading Notes Ch. 1-4
BI 315 Reading Notes Ch. 1-4 BI 315
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This 11 page Class Notes was uploaded by JordanK on Thursday February 11, 2016. The Class Notes belongs to BI 315 at Boston University taught by Dr. Widmaier in Spring 2016. Since its upload, it has received 46 views. For similar materials see Systems Physiology in Biology at Boston University.
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Date Created: 02/11/16
BI315:SystemsPhysiology SPRINGSEMESTER2016 INSTRUCTOR:DR.WIDMAIER Chapter 1 (all required except 1.8) → focus on Figures 1.1-1.9 ← Key Terms ● Physiology : the study of how living organisms function, from the function of individual molecules to the integrated functions of organ systems; maintenance of homeostasis ● Pathophysiology : state of disease, “physiology gone wrong”; when homeostasis is not maintained ● Epithelium: epithelial tissue ● Basement Membrane : extracellular protein layer that epithelial cells rest on to anchor the tissue (held by tight junctions) ● Extracellular Matrix: formed by connective tissue to provide scaffolding for cellular attachments and transmit information (chemical messengers) to regulate cell growth, activity, migration, and differentiation; fibers, collagen fibers,and elastin fibers Intro (1.1 & 1.2) ● Cell differentiation is responsible for different types of cells in the body (varying shapes & functions) ● The body is made up of 4 major types of cells, and therefore 4 types of tissues ○ muscle : includeskeletamuscle (attached through other structures to bone to produce movement, voluntary),cardiamuscle (only found in heart, involuntary), smoothmuscle (surrounds tubes in body such as blood vessels, involuntary) ○ neuron: part of nervous system; initiates, integrates, and conducts electrical signals to other cells ○ epithelial: specialized for selective secretion and absorption of ions and organic molecules and for protection; located at surfaces that cover the body or individual organs and line inner surfaces of tubular or hollow structures 1 ○ connective : connects, anchors, and supports the structures of the body; includeslooseand dense(tendons, ligaments) connective tissuebone, cartilageadiposetissues, andblood(fluid tissue) ● Organs are composed of two or more kinds of tissues in various proportions and patterns (ex: heart: neurons, cardiac muscle, adipose & epithelial tissues) ○ functional units: small subunits of an organ that perform a specific function (ex: nephrons in kidneys - all produce urine that is collectively expelled from the kidney) ● Organ systems are composed of more than 2 organs that perform an overall function together (ex: urinary system: kidneys, urinary bladder, ureters, tubes, and urethra) ○ organ systems do not function in isolation but rather in conjunction with each other (ex: blood pressure controlled by circulatory, urinary, nervous, and endocrine systems) 1.3- Body Fluid Compartments ● Internal Environment : body fluids, collectively the watery solution of dissolved substances including oxygen, nutrients, and wastes ○ intracellular fluid: fluid in all cells, 67% of total fluid in body ○ extracellular fluid: fluid outside of cells ■ 20-25% blood plasma ■ 75-80% i nterstitial fluiin the interstitium, found around and between cells ■ both fluids have similar concentrations of dissolved substances as they exchange oxygen, nutrients, wastes, etc. ■ plasma & interstitial fluid separated by blood vessel walls ● Water accounts for 55-60% of the body weight of an adult ● Compartmentalization is essential for cells as barriers between compartments determine what substances can move between compartments ○ plasma membrane in cells maintains intracellular fluid composition which is very different than extracellular fluid composition Homeostasis (1.4 & 1.5) ● Homeostasis : a state odynamic constancy between physiological variables (blood pressure, body temp, oxygen/glucose/sodium ion concentrations in blood, etc.) ○ ex) glucose levels in blood (figure 1.4): increases after eating, returns to pre-meal level with help of insulin ● Someone can be homeostatic for one variable but not another (not within homeostatic range) ○ non-homeostasis of one variable often triggers non-homeostasis in other variables too though (ex: elevated body temp causes total-body water to go down as you perspire) 2 ● Certain diseases are defined as the loss of homeostasis in one or more systems of the body ● Homeostatic control systems : compensation mechanisms that mediate responses to changes in homeostasis (ex: body producing heat when body is in an environment that is colder than internal body temp so that thset pointof the thermoregulatory system is maintained) ○ steady state is maintained: no net change in variable, but energy is being put into the system to maintain this constant condition (NOT equilibrium) ● Stability is maintained by balancing the inputs and outputs of a system ● Negative feedback system : a system in which an increase or decrease in the regulated variable causes a response that tends to move the variable in the opposite direction of the original change ○ ex) production of an active product turns off the process making it once a certain level is reached (figure 1.6); prevents unlimited production of active product ● Positive feedback system : a system that is accelerated with increase or decrease in the regulated variable, leading to an “explosive” response ○ very rare (ex: birth - pressure of baby’s head on cervix leads to secretion of oxytocin which leads to contractions to deliver baby) ● Set points can be changed in response to external stimuli (pathogens, etc.) or other changes (time of day, etc.) ○ ex) during an infection, the set point for body temp is raised (resulting in a fever) in order to kill the pathogens ○ can reflect clashing demands of different regulatory systems ● Multiple systems usually control a single parameter (ex: body temp) ○ redundancy allows for fine-tuning and regulation, even if one of the systems is not functioning properly due to disease ● Feedforward regulation : when changes in regulated variables are anticipated and prepared for before they occur; minimizes amount of deviation from set point ○ ex) body temp controls begin to heat body before cold external environment can cause body to lose heat ○ ex) smell of food causes activation of digestive enzymes before food is ingested 1.6 - Components of Homeostatic Control Systems ● Reflexes : a specific, involuntary, unpremeditated “built-in” response to a particular stimulus ○ reflexes are learned or acquired and always subject to alteration by learning ○ reflex arc: pathway mediating a reflex (stimulus →afferent pathway → integrating center compares to set point → efferent pathway → response) ● Stimulus : a detected change in the internal or external environment 3 ○ detected by receptors ● Integrating centers often receive signals from many receptors and respond to different types of stimuli ○ output of the center reflects the net effect of afferent input ○ output of the center (efferent response) leads to a negative feedback system between strength of stimuli and strength of response ■ does NOT always occur (ex: activation of digestive enzymes due to smell of food does not eliminate smell of food) ● Muscles and glands are the major effectors of biological control systems ● Hormone : chemical messenger secreted into the blood by the endocrine system; can act on numerous types of cells simultaneously as they circulate through body ○ can act as the efferent pathway in a reflex arc instead of nerves (thus, a hormone-secreting gland acts as the integrating center) (ex: increase in glucose concentration in blood stimulates insulin production from pancreas) ● Local homeostatic responses : initiated by a change in the external or internal environment, produces an effect that counteracts the stimulus ○ DIFFERENT than reflexes, as they only occur in the immediate area of the stimulus 1.7 Intercellular Chemical Messengers in Homeostasis ● 4 categories of chemical messengers ○ hormones : allows hormone-secreting cells (endocrine glands) to communicate with distant target cellsvia the bloodstream ○ neurotransmitters : released from the endings of neurons onto other neurons, muscle cells, or gland cells ○ paracrine substances: involved in communication between local cells ○ autocrine substances: involved with communicating on the same cell that released the signal ● messengers may be paracrine and autocrine at the same time ● gap junctions do not require chemical signals as cells with gap junctions are physically connected to other cells 1.9 - General Principles ● homeostasis is essential for health and survival ● organ systems function in relation to each other ● most physiological functions are controlled by numerous regulatory systems (often working against each other) ● communication between cells/tissues/organs is essential for homeostasis and for the integration of physiological processes ● the exchange of materials between compartments and cellular membranes is controlled ● physiological processes follow the laws of chemistry and physics 4 ● physiological processes require the transfer and balance of matter and energy ● structure determines, and has evolved with, function Chapter 2 (all required except 2.1-2.3 and pg. 38-39) → look at figures 2.4, 2.5, and 2.8 even though complementary reading isn’t required ← 2.4 - Classes of Organic Molecules ● organic chemistry: the study of carbon-containing molecules found in living organisms ○ macromolecules : extremely large molecules (thousands of atoms) ○ polymers : large molecules, made up of many monomers linked together ● carbohydrates : C, H, O ○ 1% of body weight ○ important for energy and energy storage ○ presence of -OH groups in a carb make it water-soluble ○ monomers: monosaccharides ; polymers:polysaccharides (ex:glycogen) ○ simplest sugars: monomer called lucose(CH O) 6 12 6 ■ most monosaccharides are 5 or 6 Cs ○ disaccharides: 2 monomers (ex: sucrose - table sugar: glucose + fructose) formed by dehydration reaction ○ hydrolysis (breakdown) of glycogen releases stored energy ● lipids: C, H ○ nonpolar, low solubility in water ○ 15% of body weight, 40% organic matter in body ○ fatty acids:chain of C and H with an acidic carboxyl group at one end ■ saturated: all single bonds ■ unsaturated: one (monounsaturated) or more (polyunsaturated) double bonds ● trans: Hs are on opposite sides of the double bond, contributes to longer storage for food and altered flavor/consistency; bad for health ■ important for energy/cellular metabolism and cell signaling ○ triglycerides: glycerol plus 3 fatty acid chains (not always identical chains) ■ majority of lipids in body ■ found in blood, synthesized in liver ■ serve as an energy reserve (hydrolysis of chains from glycerol releases energy) ○ phospholipids : third fatty acid in triglyceride is replaced by phosphate (linked to a small polar/ionized nitrogen-containing group usually) ■ amphipathic molecules: fatty acids are hydrophobic but phosphate is hydrophilic ■ forms bilayers of cell membranes 5 ○ steroids: basic skeleton is 4 interconnected carbon rings (ex: cholesterol, cortisol, sex hormones) ● proteins: C, H, O, N ○ 17% of body weight, 50% organic material in body ○ monomers: amino acids (20 different ones exist; may be polar or nonpolar or ionized) ■ peptide bond : covalent bond between 2 amino acids (many linked amino acids is aolypeptide) ○ primary structure: the number of amino acids and the specific sequence ■ easiest structure of protein to determine ■ mutations in primary structure alter upper structures due to changes in amino acid interaction (ex: sickle cell anemia caused by single amino acid change) ○ secondary structure: basic shape of amino acid chain due to hydrogen-bonding and other interactions between atoms in amino acids ■ alpha helix orbeta pleated sheet ○ tertiary structure: shape at which protein is functional, due to hydrogen-bonds, ionic interactions, hydrophobic/philic regions, disulfide bonds, van der Waals forces ○ quaternary structure: “multimeric proteins”; many polypeptides together (ex: hemoglobin - 4 polypeptides) ● most molecules are made up of many of the 4 groups of organic molecules (ex: glycoproteins) Chapter 3 (only Section C and 3.10 required; Sections A and D are Review) 3.8 - Binding Site Characteristics ● ligand : any molecule that is bound to a protein by electrical attractions between oppositely charged ionic or polarized groups or by weaker attractions due to hydrophobic forces between nonpolar regions on two molecules ● binding on the binding siteis generally reversible ○ proteins may have many binding sites and may bind more than one ligand ○ binding of ligand usually induces a conformational change, which changes the protein’s function ○ binding is selectively specific (some binding sites are more selective than others) → chemical specificity (figure 3.26) ● in order for a ligand to bind to its protein, the ligand must be close to the protein’s surface (they fit together like puzzle pieces) → depends on shape ● the degree of specificity of binding sites determines the side effects of therapeutic drugs (will they bind to other binding sites unintentionally? what will that cause?) ● affinity:the strength of the ligand-protein binding ○ determines how long the bound ligand will remain on the protein ○ high-affinity (tightly bound) or low-affinity (loosely bound) ■ determines how much of a ligand is needed to bind enough 6 ○ depends on strength of interaction (different proteins that bind the same ligand may have different affinities) ■ shape of ligand and binding site influences strength of interaction ● saturation : the fraction of total binding sites that are occupied at a given time ○ 100% = all binding sites are bound by ligands (0% = none) ○ depends on concentration of unbound ligand and affinity of binding site for ligand ■ higher concentration = higher probability that ligands will be bound (= higher saturation) ■ low affinity = ligands are easily bumped off receptors (=lower saturation & lower biological response, need higher concentration to maintain a high degree of saturation) ○ higher degree of saturation correlates to a higher effect caused by the ligand binding to its receptor ● competition can occur if more than one type of ligand can bind to the same receptor ○ one ligand’s biological response may overshadow another’s if it has a higher concentration and can thus bind to more binding sites ○ many drugs compete with natural ligands in this manner 3.9 - Regulation of Binding Site Characteristics ● allosteric modulation ○ occurs when a protein has two different binding sites on it; the binding of one ligand changes the shape of the protein, thus enabling or preventing the second ligand to bind ○ requires non-covalent bindingof modulator molecule ○ functional site: site that carries out protein’s physiological function when a ligand is bound to it ■ can regulate other functional sites on same protein when bound = cooperativity ● ex) when oxygen binds to the first binding site in hemoglobin, the affinity of other sites for oxygen increases ○ regulatory site : site that alters the functionality of the protein when its ligand (modulator molecule) binds to it & changes the protein’s shape ■ can turn functional site on/off or increase/decrease its affinity for ligands ● covalent modulation ○ the shape and activity of a protein is altered by the covalent bonding of a charged chemical group to the protein’s side chains ○ most often, a phosphate group (net negative charge, phosphorylation ) is added ■ enzymes that control phosphorylation: protein kinase(requires ATP) ■ enzymes that remove phosphate groups: p hosphoprotein phosphatases ■ kinases are specific to certain proteins; many types of kinases can exist in one cell (phosphatases are less specific) 7 ○ similar to allosteric modulation, functional sites can be turned on/off or change in affinity can occur ● covalent modulation can be controlled by allosteric modulation (ex: a kinase must be allosterically turned on in order to modulate other proteins) & vice versa 3.10 - Chemical Reactions ● straight-forward stuff from gen chem but basic overview: ○ chemical reactions are the breaking of chemical bonds followed by the making of new ones ○ energy cannot be created nor destroyed ○ one calorieis the amount of heat needed to raise 1 g of water by 1 C ○ rate of reaction increases directly with concentration of reactants ■ law of mass action : effect of reactant and product concentrations on the direction in which the net reaction proceeds ○ activation energy must be reached for reaction to occur ○ catalyst: substance/molecule that decreases the activation energy needed to begin a reaction and is not actually involved in reaction (can be infinitely reused) ○ chemical equilibrium when the ratesof the forward and reverse reactions are equal ○ generally, reactions that release a large amount of energy are irreversible Chapter 4 (all required except figures 4.11, 4.15, 4.21 and table 4.1; can skip section on endo/exocytosis in 4.4) 4.1 - Diffusion ● simple diffusion : random thermal motion of molecules in a liquid or gas will eventually distribute themselves uniformly throughout a container ○ higher concentration → lower concentration ○ at equilibrium, all molecules are still moving but equally in all directions ○ ex) oxygen, nutrients, etc. through blood vessels (circulatory system) ● flux : amount of material crossing a surface in a unit of time ○ net flux: the difference between 2 one-way fluxes, determines net gain/loss of molecules in a compartment per unit of time (overall net flux is always high → low) ○ depends on temperature (increased temp = faster flux), mass of molecule (larger = slower), surface area (greater S.A. = more space for diffusion = faster flux), and medium (rapid diffusion in air compared to water) ● diffusion equilibrium : 2 one-way fluxes are equal in magnitude in opposing directions (equal rates of diffusion at equal concentrations) ● diffusion times increase in proportion to the square of distance over which molecules diffuse (1:1, 2:4, 3:9, etc.) ● Fick’s first law of diffusio: J = PA(0 i ○ J = rate of diffusion, P = membrane permeability coefficient, A = S.A., C = concentration (tside and nside the cell) ○ P is experimentally determined, reflects of passing through membrane ● lipid bilayer is a major limiting factor in membrane diffusion 8 ○ nonpolar molecules diffuse rapidly (membrane is nonpolar), polar molecules can if they are tiny, usually cannot at all (large P) ○ ex) nonpolar: oxygen, CO 2 fatty acids, steroid hormones ● ion channels allow diffusion of ions + + - 2+ ○ Na , K, C, and Caetc. ○ channel protein(s) with hole in middle; show selectivity for the type of ion(s) that can diffuse through it based on channel diameter, electrical attraction/repulsion of ion (+/-), and number of water molecules associated with ion ○ channel gating : process of opening/closing ion channels ■ ligand-gated ion channels : opens/closes due to binding of specific molecules to channel proteins (allosteric or covalent shape change) ■ voltage-gated ion channels : opens/closes due to change in membrane potential ■ mechanically-gated ion channels : opens/closes due to physically deforming the membrane ○ an ion can pass through several types of ion channels ● membrane potential : separation of electrical charge across the plasma membrane ○ influences movement of ions across membrane (positive ions will influx to negative interior of cell - regardless of ion concentration!) ● electrochemical gradient : the effects of concentration and charge on ion movement across a membrane 4.2 - Mediated-Transport Systems ● transporters : transmembrane proteins that mediate diffusion of molecules that are too polar to diffuse through membrane or too large to diffuse through channels ○ process called mediated transport ○ transported solute must bind to specific site on the transporter, which causes a conformational change that opens the binding site on the other side of the membrane ○ molecules can move in either direction ○ much slower process than ion channels (must move one molecule at a time) ○ specific to a particular molecule or class of molecules (ex: amino acids or sugars) ● factors that determine magnitude of solute flux through mediated transport are solute concentration, affinity of transporters for solute, number of transporters in membrane, rate of conformational change of transporter ● facilitated diffusion: net flux of molecules from a higher → lower concentration; does not require energy ○ do not confuse with simple diffusion (diffusion of molecules w/o transporter)! ○ ex) GLUTs: glucose transporters (large, polar molecule) ● active transport : uses energy for net flux of molecules from a lower → higher concentration; “pumps” ○ primary active transport : direct use of ATP to move molecules 9 ■ transporter used: ATPase; hydrolyzes ATP and phosphorylates itself, which changes affinity of its solute binding site ■ ex) Na/K-ATPase pump ; moves 3 Na+out of cell while moving 2 K into cell ● binds sodium, causes phosphorylation and ATP hydrolysis ● conformational change releases sodium out of cell and exposes potassium binding sites ● binds potassium, causes dephosphorylation which returns protein to original conformation & release potassium outside ● plays role in establishment of membrane potential (-70 mV) 2+ ■ also keeps Caoutside of cell ○ secondary active transport : use of electrochemical gradient across membrane to move molecules ■ movement of molecule occurs by an ion moving down its electrochemical gradient ■ transporters have a binding site for an ion and a binding site for the molecule + ■ ex) binding of Na ion to transporter to be moved into cell (down its gradient) allows binding of a solute to move into cell (against concentration) (then Nais pumped back out of cell) ■ creation and maintenance of electrochemical gradient is dependent on the action of primary active transporters ○ cotransport : actively transported solute in secondary active transport moves in same direction as sodium ion (into cell) (symport) ○ countertransport : actively transported solute in secondary active transport moves in opposite direction as sodium ion (out of cell) (antiport) ● distribution of substances in intracellular and extracellular fluid is often unequal due to transport mechanisms 4.3 - Osmosis ● aquaporins : membrane proteins that form channels specifically for water to diffuse ○ number per cell varies by cell type ○ number can be altered by various signals (ex: number of aquaporins in kidney cells of dehydrated person increases to retain water) ● concentration of water molecules in pure water: 55.5 M (1000 g of 18 g/mol water) ● osmosis: net diffusion of water across a membrane ○ water concentrations change with added/removed solute (decrease/increase in water concentration respectively) → depends only on number of particles, not on chemical nature of solute (*some molecules can dissociate into 1+ ions) ● osmolarity : the total solute concentration of a solution (ex: 1 M solution of glucose = 1 osmol; but 1 M NaCl solution = 2 osmol; 1 M glucose + 1 M NaCl solution = 3 osmol) ○ higher osmol = lower water concentration (vice versa) ■ 55.5 M water - osmol of solute = new M of water ■ osmolarity of extracellular fluid: 285-300 mOsm 10 ● if membrane is permeable to water but impermeable to solute ( semipermeable membrane ), only the water will move to balance the concentrations → change in volume of cell ○ osmotic pressure : the pressure that must be applied tprevent the net flow of water in a certain direction (greater osmolarity = greater pressure; more water wants to balance concentration of solution with high osmolarity) ○ nonpenetrating solutes : solutes that cannot cross the plasma membrane + - + (ex: Naand Clon outside of cell, and organic solutes (large & polar) on inside of cell) ● isotonic : intracellular and extracellular osmolaritienonpenetratingsolutes (NOT total solutes) are the same; no change in cell size ○ hypotonic : lower nonpenetrating solute concentration on the outside of cell; causes swelling of cells as water moves in ○ hypertonic : higher nonpenetrating solute concentration on outside of cell; causes cells to shrink as water leaves ● isoosmotic : equal osmolarities on inside and outside of cell, regardless of nonpenetrating or penetrating solutes ○ hypoosmotic and hyperosmotic ○ DO NOT CONFUSE with tonicity ( → only accounts for nonpenetrating molecules, osmolarity accounts for all) 4.5 - Epithelial Transport ● epithelial cells line hollow organs/tubes and regulate absorption/secretion of substances across these surfaces ○ apical membrane : side that faces the hollow or fluid-filled chamber/tube ○ basolateral membrane : side that faces opposite, usually to network of blood vessels ● paracellular pathway : diffusion occurs between adjacent cells in epithelium ○ limited by tight junctions: leaves small area available for diffusion, usually only see movement of small ions and water ● transcellular pathway : diffusion of substance across one side of membrane (apical or basolateral), through cytosol, and out the other side ○ occurs via diffusion or mediated transport ○ permeability characteristics of basolateral and apical membranes are Not the same: most substances go from low → high concentration and only cross one of the membranes (ex: absorption of material from GI tract) + ○ ex) Na diffuses into cell from apical side (high → low) but is pumped out on basolateral side (low → high) ■ causes movement of water as well (basis for how kidneys absorb water from urine back into blood or how water is absorbed from intestines) 11
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