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Human Physiology Test 1 Notes.docx

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Department
Kinesiology & Health Science
Course
KINE 2011
Professor
Gillian Wu
Semester
Fall

Description
Human Physiology Exam Notes Chapter 1 – The Foundation of Physiology  Human physiology – study of the functions of our body  Exercise physiology – the structures and functions of our bodies are altered when exposed to both acute and chronic sessions of exercise  Teleological approach – explains body functions in terms of meeting a bodily nee, explains why or purpose of body processes  Mechanistic approach – cause and effect  Anatomy – the study of structure of the body Levels of Organization in the Body Chemical Level  Atoms are the smallest building blocks of all nonliving and living matter  Oxygen, carbon, hydrogen, and nitrogen – 99%  Calcium, phosphorous, and potassium – 1% Cellular Level  The cell – the basic or fundamental unit of both structure and function o The smallest unit of life  Plasma membrane o Thin, oily barrier o Encloses the contents of the cell o Control movements  Organisms o Independent living o Single celled – bacteria and amoebas o Complex – humans  Cell differentiation – body is made up of many different specialized types of cells  Basic cell function o Food and oxygen o Provide energy o Remove CO2 and waste o Synthesize proteins o Control exchange of material o Moving materials, cell activities o Respond to change o Reproducing for most cells (not nerve or muscle)  Specialized cell function o Glandular cell of digestive system, protein synthesis, produce and secrete digestive enzymes o Kidney cells control the exchange of materials between cells, and waste o Muscle contraction moves internal structures to shorten muscles o Nerve cells generate, transmit, and store information in electrical impulses Tissue Level  Cells of similar function  For types of tissue cells  Muscle tissue – contracting and generating force, three types of muscle tissue: skeletal muscle (moves the skeleton), cardiac muscle (pumps blood), and smooth muscle (encloses and controls movement through hallow tubes/organs)  Nervous tissue – electrical impulses, one body part to another  Epithelial tissue – exchange of materials between the cell and environment. Two types: epithelial sheets and secretory glands o Lumen – cavity within a hallow organ or tube o Selective o Glands – secretion, created by epithelial tissue that dip inwards from the surface and develop secretory capabilities  Exocrine (secret through ducts to outside of the body) and endocrine (hormones into the blood)  Connective tissue – few cells dispersed within an abundance of extracellular material o Connects, supports, and anchors body parts o Loose connective tissue – attaches epithelial tissue to underlying structures o Tendons – attach skeletal muscles to bones o Bone – gives body shape o Blood – transports material o Expect for blood, the cells within connective tissue produce specific structural molecules that they release into the extracellular space between cells  Elastin – rubber band like protein fiber , stretching and recoiling  The stomach is made up of all four tissue type Body System Level  Groups of organs  Digestive system – mouth, salivary glands, throat, esophagus, stomach, pancreas, liver, gallbladder, small intestine, and large intestine  Human body has 11 systems o Circulatory, digestive, respiratory, urinary, skeletal, muscular, integumentary, immune, nervous, endocrine, and reproductive Organism Level  Do not act in isolation from one another  Interplay of multiple systems Homeostasis and Homeokinesis  Homeostasis is the ability of a cell or organism to regulate its internal conditions  Using feedback systems  If internal body temperature were to decrease, the body would enact processes such as shivering to increase internal body temperature  We do not have a specific set point but more a physiological range  Homeokinesis suggest suggests that organisms will achieve equilibrium in body functions by dynamic processes (continuous change)  In healthy lungs, control of airway caliber is homeokinetic  Homeokinetic state – to exist using regular non random variation  Homeostasis attempts to minimize change to maintain a stable internal environment only acting in response to the internal environment moving away from the set point  Homeokinesis regularly initiates small non-random changes to maintain a stable internal environment  Both try to retain a steady internal environment  Homeokinesis by initiating change, and homeostasis by responding to change Concepts of Homeostasis Homeostasis  Commonly using negative feedback systems to minimize variation and maintain health  The cells in multicellular organisms cannot live without contributions from other body cells because the vast majority of cells are not in direct contact with the external environment  A singe celled amoeba can directly obtain nutrients and oxygen from, and eliminate waste into, its immediate external surroundings  But a muscle cell in a multicellular organism needs nutrients and oxygen, but cannot directly make these exchanges because cell is isolated from external environment  How does muscle cell make these vital exchanges? o In the presence of a watery internal environment with which the body cells are in direct contact and make life sustaining exchanges Body cells  The fluid contained within all body cells is called intracellular fluid (ICF)  The fluid outside the cell is called extracellular fluid (ECF)  The extracellular fluid is the internal environment of the body, the fluid environment in which the cells live  Intracellular fluid is inside of each cell and the external environment is outside the body  You live in the external environment; your cells live within the body’s internal environment  The extracellular fluid is made up of 2 components o Plasma – the fluid portion of the blood o Interstitial fluid – surrounds and bathes the cells  Each body cell must help maintain the composition of the internal environment so that this fluid continuously remains suitable to support the existence of all the body cells  An amoeba does nothing to regulate its surroundings Body Systems  The functions performed by each body system contribute to homeostasis  Cells make up the body systems  Homeostasis is essential for the survival of each cell and each cell, through its specialized activities, contributes as part of a body system to the maintenance of the internal environment shared by all cells  Homeostasis is not a rigid, fixed state, or absolute setting, but a dynamic, steady state, in which changed occur but are minimized by multiple dynamic equilibrium adjustments  Chronic adaptations make the body more efficient in responding to an ongoing or repetitive challenge  Exercise includes both short term (acute) responses and chronic adaptations Factors homeostatically regulated  Concentration of nutrient molecules  Concentration of oxygen and carbon dioxide  Concentration of waste products  pH  Concentration of water, salt, and other electrolytes  Volume and pressure  Temperature Contributions of the body systems to homeostasis  The 11 body systems contribute to homeostasis in the following important ways  Circulatory system o Transports materials such as oxygen, carbon dioxide, wastes, electrolytes, and hormones o Thermoregulation by moving heat to the periphery from the core  Digestive system o Breaks down food into small nutrients o Transfers water and electrolytes to internal environment  Respiratory system o Receives oxygen o Eliminates carbon dioxide o Maintain pH  Urinary system o Removes excess water, salt, acid, and other electrolytes from the plasma  Skeletal system o Provides support and protection for the soft tissue organs o Storage for calcium o Bone marrow is source of blood cells  Muscular system o Basis of movement o Attaches via tendons to bones o Move forward or move away from harm o Heat generated from muscle contraction is important in temperature regulation  Integumentary system o Outer protective barrier that prevents internal fluid from being lost from the body and foreign microorganism from entering o Regulating body temperature o Sweat production o Regulation of warm blood through the skin  Immune system o Defends against foreign invaders o Repairing and replacing injured or worn out cells  Nervous system o Controls and coordinates bodily activities that requite swift responses o Detecting and initiation reactions to changes  Endocrine system o Communication system o Hormones secretion o Duration rather then speed o Concentration of nutrients, kidney function  Reproductive system o Not essential to homeostasis Homeostatic Control Systems  Which is a functionally interconnected network of body components that operate to maintain a given factor in the internal environment  To maintain homeostasis, the control system must be able to o Detect deviations from normal in the internal environment (receptor) o Integrate this information with any other relevant information (control center) o Trigger the needed adjustments responsible for resorting this factor within the normal range (effector) Local or Body Wide  Homeostatic control mechanisms can be grouped into two local classes o Intrinsic and extrinsic controls o Intrinsic (local) controls  Build into or inherent in an organ  For example: exercising skeletal muscle rapidly uses up oxygen t generate energy  The oxygen concentration falls  This local chemical change acts directly on the smooth muscle in the wall of the blood vessels that supply the exercising muscle  Causing the smooth muscle to relax so that the vessels dilate  An increased amount of blood flows through into the exercising muscle, bringing in more oxygen o Extrinsic controls  Initiated outside an organ to alter the activity of the organ  Achieved by two major regulatory systems  Nervous and endocrine systems  Extrinsic control permits synchronized regulation of several organs to a common goal  Intrinsic controls are self serving for the organ in which they occur  To maintain blood pressure within the range, the nervous system simultaneously acts on the heart and the blood vessels throughout the body to increase or decrease blood pressure  Feedback – responses made after a change has been detected  Feedforward – describes responses made in anticipation of a change Negative feedback  A change in homeostatically controlled factors trigger a response that seeks to maintain homeostasis by moving the factor in the opposite direction of its initial change  Room temperature is a controlled variable held within a narrow range by a control system  Actual, compare with desired, and adjust the output  Sensor – provided information  Thermostat acts as control center (integrator) which compares the sensor’s input with the optimal range and adjusts the furnace output  Effector – the component of the control system used to bring about the desired effect  Negative feedback loop  When temperature monitoring nerve cells in the hypothalamus detect a decrease in the body temperature below the physiological range, they signal other never cells in a control center, which initiate shivering  When body temperature rises, the temperature monitoring nerve cells turn off the stimulatory single to the skeletal muscles, stopping the shivering Positive feedback  Negative feedback is used to resist change and add stability to the internal environment  Positive feedback the output enhances or amplifies a change so that the controlled factor continues to move in the direction of the initial change  Occurs much less  Used in child birth  Hormone oxytocin causes powerful uterine contractions  Brings bout the release of more oxytocin, which causes stronger uterine contractions  Heatstroke – when temperature regulating mechanisms are unable to cool the body sufficiently Feedforward mechanism and anticipation  Anticipates change in a regulated factor  When a meal is still in the digestive tract, a Feedforward mechanism increases secretion of a hormone (insulin) that will promote the cellular uptake and storage of ingested nutrients after they have been absorbed from the digestive tract  Helps limit the rapid rise in nutrients after absorption into the blood Disruptions in homeostasis  Pathophysiology refers to the abnormal functioning of the body associated with diseases Chapter 2 – Cell Physiology  The cell theory o The cell is the smallest unit capable of life o Function of that cell depends on the specific structure o Cells are building blocks of all pants and animals o Organisms structure and function depends on capabilities of the cells o All new cells and new life arise from previous cells o Cells are all similar in structure and function Observation of Cells  Larger species have greater number of cells not bigger cells Overview of Cell Structure  Single skeletal muscle cell is cylindrical and elongated, but can vary in length  Every muscle cell contains multiple nuclei (multinucleated)  Depending on type of muscle cells (type 1 or type 2) there maybe difference in the number of mitochondria  Most cells have three major sub divisions o Plasma membrane, nucleus and cytoplasm Cellular Metabolism  Intermediary metabolism – chemical reactions inside the cell that involve the degradation, synthesis, and transformation of small organic molecules  Anabolic processes – favor the synthesis of molecules for building up organs and tissue  Catabolic processes – favor the breakdown of complex molecules into more simple ones  Anabolic metabolism – it takes energy to combine simpler molecules into more complex molecules  Source of energy for the body is the chemical energy stored in the carbon bonds of ingested food  Adenosine triphosphate (ATP) – consists of adenosine with three phosphate groups  When a high energy bond is broken energy is released  Cells use ATP to pay for the cost of operating body cells  To obtain immediate useable energy cells split the terminal phosphate bond of ATP, which yields in adenosine diphosphate (ADP)  The chemical pathways for regeneration of ATP involved three separate processes: o Creatine phosphate (CP; substrate level phosphorylation) o Anaerobic glycolysis o Aerobic metabolism  Three different mitochondrial steps o Glycolysis (both aerobic and anaerobic) o Tricarboxylic acid cycle (TCA cycle; aerobic) o Electron transport chain (ETC; aerobic) Pathway for Production of ATP Substrate level phosphorylation  Substrate level phosphorylation of ADP using creatine phosphate (CP)  Creatine phosphate is the first energy store trapped at the onset of contractile activity  It is not stored in the mitochondria, but in the cytosol  Like ATP, CP contains a high energy phosphate group  The energy released from the hydrolysis (reaction using H2O) of CP, along with the phosphate, can be donated directly to ADP to form ATP  This reaction which is catalyzed by the skeletal muscle cell enzyme creatine kinase, is reversible  Energy and phosphate from ATP can be transferred to creatine to form CP  CP + ADP  Creatine + ATP  A rested muscle contains about five times as much CP as ATP  Most energy us stored in skeletal muscle is in the form of CP  When the skeletal muscle starts to contract using ATP to accomplish cellular work , the CP replenishes the ATP  CP levels tend to decrease more greatly than ATP levels  There tends to be a large change in CP levels with a minimal change in the level of ATP  ATP can be formed rapidly because only one enzymatic reaction is involved Glycolysis  10 separate reactions that break down the simple 6 carbon sugar molecule glucose into 2 pyruvic acid molecules which contain 3 carbons  Not very efficient in terms of energy extraction  The next yield is only 2 molecules of ATP per glucose molecue  The low energy yield of glycolysis is not enough to support the body’s demand for ATP  This is where the mitochondria comes to play  Persons with McArdle disease for example are unable to break down glycogen to glucose and this produce energy Tricarboxylic acid cycle  Pyruvic acid enters the mitochondrial matrix through the carrier protein monocarboxylate transporter  Located on the inner mitochondrial membrane  Pyruvic acid then interacts with the enzyme pyruvate dehydrogenase (PDH) and enters into the TCA cycle where further ATP is produced via aerobic metabolism  The enzyme PDH controls the movement of pyruvic acid into the TCA cycle  Decarboxylation occurs which is the removal of a carbon and the formation of carbon dioxide  As well as the transfer of a hydrogen to nicotinamide adenine dinucleotide (NAD+) forming NADH  Carbon dioxide is eliminated from the body via the cardiorespiratory system  Once the pyruvic acid is converted to acetyl coenzyme A it is ready to enter the TCA cycle  Acetyl CoA enters the Krebs cycle which has 8 separate reactions that are directed by the enzymes of the mitochondrial matrix  Acetyl CoA is a 2 carbon molecule that enters the TCA cycle and combines with oxaloacetic acid (4 carbon molecule) to form a 6 carbon molecule, citric acid  Coenzyme A is removed from acetyl CoA, allowing it to be reused in the conversion of more pyruvic acid intro acetyl CoA  Citric acid turns to isocitric acid, which then becomes alpha-ketoglutaric acid o A hydrogen is removed and then carbon via CO2 o Hydrogen is again removed and CO2 forms o The new structure then attaches itself to coenzyme a forming succinly CoA consist of 4 carbons  Coenzyme A is removed and a phosphate group is added  The group is transferred later via GTP to ADP, forming ATP  More hydrogen is removed forming fumaric acid, water is added and then more hydrogen is again removed  This last removal of hydrogen and acceptance of hydrogen by NAD+ forms the molecule that we initially being with – oxaloacetic acid  2 carbons are removed from the 6 carbon citric acid molecule, converting it back into the 4 carbon oxaloacetic acid, which is now available at the top of the cycle to pick up another acetyl CoA  The released carbon atoms are converted to 2 molecules of CO2  This CO2 passed out of the mitochondrial matrix and enters the blood  The blood carries the CO2 to the lungs  Hydrogen atoms are also removed during the cycle  These hydrogen’s are caught by NAD+ and FAD  Transfer of hydrogen converts NADH and FADH2  ATP is not directly produced by the citric acid cycle  ADP + GTP  ATP + GDP  Each glucose molecule is converted into 2 acetyl CoA , making to turns of the TCA cycle  Two more ATP Electron transport chain  NADH and FADH2 enters the ETC  Consists of electron carrier molecules located in the inner mitochondrial membrane lining the cristae  The high energy electrons are extracted from the hydrogen’s held in NADH and FADH2 and are transferred through a series of steps from one electron carrier molecule to another  Converted back to NAD+ and FAD  NAD+ and FAD serve as the link between TCA and ETC  Electrons falling to lower energy levels with each step  Electrons are passed to molecular oxygen derived from the air  Electrons bound to oxygen are in their lowest energy state  Final electron acceptor is oxygen  This negatively charged oxygen combines with positively charged hydrogen ions to form water  Chemiosmotic mechanism o At 3 sites in the ETC chain, the energy released during the transfer of electrons is used to transport hydrogen ions across the inner mitochondrial membrane from the matrix to the space between the membranes o Hydrogen ions are more concentrated in the mitochondrial inter membrane space , because of the difference in concentration, the transport hydrogen ions have a strong tendency to flow back into the matrix o Hydrogen ions that return to the matrix bear the enzyme ATP synthase, which is activated by the flow of hydrogen ions o On activation, ATP synthase convers ADP + Pi to ATP o Providing 32 more ATP molecules for each glucose Aerobic Versus Anaerobic Conditions  Anaerobic – glucose does not proceed beyond glycolysis  Aerobic – when oxygen is used, 36 molecules of ATP per glucose  Food + O2  CO2 + H2O + ATP ATP for Synthesis, Transport, and Mechanical Work  Synthesis of new chemical compounds  Membrane transport  Mechanical work The Plasma Membrane  Thin layer of lipids and proteins that forms the outer boundary of every cell  Maintains ion concentrations  Cells survival, maintain homeostasis, and function cooperatively and in coordination with surrounding cells  Trilaminar structure – two dark layers separated by a light middle layer  Three layered sandwich appearance Membrane structure and composition  Lipids  Proteins, and some carbohydrates  Phospholipids – polar head containing a negatively charged phosphate group and two non polar fatty acid tails  Polar end is hydrophilic  Nonpolar end is hydrophobic  Assemble into a lipid bilayer  The outer surface is exposed to extracellular fluid  Inner surface is in contact with the intracellular fluid  Not rigid, but fluid  Cholesterol also contribute to fluidity and stability of membrane o Tucked between the phospholipid molecules o Prevent the fatty acid chains from packing together and crystalizing  Cell can change shape  Membrane proteins o Attached or inserted  Fluid mosaic model o Membrane fluidity  Small amount of membrane carbohydrate is located on the outer surface making the membrane sugar coated  Shot chain carbohydrates bound to membrane proteins and lipids o Glycoproteins and glycolipids Lipid bilayer  Barrier  Fluidity Membrane proteins  Water filled pathways or channels across the lipid bilayer o Water soluble molecules and small ions can go through channels o Sodium can pass through sodium channels o Potassium can pass through potassium channels  Carrier molecules o Transfer specific substances across the membrane that are unable to cross on their own o Particular molecule  Docking – marker acceptors o Bind in a lock and key o Secretory vesicles o Opens up and empties its content to the outside by exocytosis  Membrane bound enzymes o Control specific chemical reactions at either the inner or outer cell surface o Cells are specialized in the types of enzymes embedded within their membrane  Receptor sites o Recognize and bind with specific molecules in the cells environment o Chemical messengers in the blood such as water soluble hormones can influence only the specific cells that have receptors for a given messenger  Cell adhesion molecules (CAMs) o Outer membrane surface and from loops or hooks that the cell use to grip each other and to grasp the connective tissue fibers that interlace between cells o Cadherins - on the surface of adjacent cells, interlock in a zipper like fashion to help hold the cells within tissues and organs together o Integrins - span the membrane, structural link between the outer membrane surface and its extracellular surroundings but also connect the inner membrane surface to the intracellular cytoskeletal scaffolding o Signaling molecules Self recognition  Short sugar chains serve as self identity markers  Trademark  Tissue growth Cell to Cell Adhesions  Bind groups of cells together into tissues and package them further into organs  Carbohydrate chains on the membrane surface  Cells are held together by 3 different means o Extracellular matrix o Cell adhesion molecules in the cells plasma membrane o Specialized cell junctions Biological glue  Extracellular matrix (ECM)  Meshwork of fibrous proteins embedded in a watery gel like substance composed of complex carbohydrates  Glue  The watery gel provides pathway for diffusion of waste and other water soluble traffic between blood and tissue cells  Called the interstitial fluid  3 major types of protein fibers: collagen, elastin, and fibronectin o Collagen – cable like fibers or sheets that provide tensile strength  Scurvy – vitamin C deficiency, tissue of skin and blood vessels become fragile, leads to bleeding in the skin and mucus in membranes o Elastin  Rubber like protein fiber  Easily stretchable and recoiling  Found in lungs o Fibronectin  Holds cell in position  Promotes cell adhesion Cell junctions  Desmosomes (adhering junctions), tight junctions (impermeable junctions), or gap junctions (communicating junctions) Desmosomes  Spot rivets that anchor together two closely adjacent but non touching cells  Consists of two components o A pair of dense, button like cytoplasmic thickenings known as plaque located on the inner surface of each of the two adjacent cells o Strong glycoprotein filaments containing cadherins that extend across the space between the two cells and attach to the plaque on both sides o Bind adjacent plasma membranes together so they resist being pulled apart Tight junctions  Adjacent cells firmly bind with each other at points of direct contact to seal off the passageway between the two cells  Epithelial tissue  Kiss sites – sites of direct fusion of junctional proteins on the outer surfaces of the two interacting plasma membranes  Prevent materials from passing between the cells Gap junctions  A gap exists between adjacent cells with are linked by small connecting tunnels formed by connexons  Connexon is made up of 6 protein subunits arranged in a hallow like tube structure  Two connexons extend outwards one from each of the plasma membranes and join end to end to form the connecting tunnel  Communicating junctions  Permit small water soluble particles to pass between the connected cells but precludes passage of large molecules  Direct transfer of small signaling molecules from one cell to the next Overview of Membrane Transport  Permeable – if a substance can cross the membrane  Impermeable – substance cannot pass  Selectively permeable – some particles to pass  Two properties of particles influence whether they can permeate the plasma membrane without any assistance o Relative solubility of the particle in lipid o The size of the particle  Highly lipid soluble particles can dissolve in the lipid bilayer and pass through the membrane  Uncharged or nonpolar molecules are highly lipid soluble and readily permeate the membrane  Charged particles and polar molecules have low lipid solubility but are very soluble in water  Only ions for which specific channels are available and open can permeate the membrane  Passive forces – no energy  Active force – need energy Unassisted Membrane Transport  Passive transport o Diffusion down a concentration gradient o Movement along an electrical gradient Passive diffusion of particles  Uniform spreading out of molecules – diffusion  Concentration gradient of chemical gradient – difference in concentration between two adjacent areas  Net diffusion – difference between two opposing movements  Steady state  Down concentration gradient – from area of higher concentration to lower concentration  No energy is required Fick’s law of diffusion  Magnitude of the concentration gradient o The greater the difference in concentration the faster the rate of net diffusion  Permeability of the membrane to the substance o The more preamble the membrane, the more rapid  The surface area of the membrane across which diffusion is taking place o The larger the surface area the greater the rate of diffusion  Molecular weight of the substance  The distance through which diffusion must take place Passive diffusion of ions  Movement of ions is affected by their electrical charge  Like charges repel each other  Opposites attract  A difference in charge between two adjacent area this produces an electrical gradient that promotes the movements of ions towards the area of opposite charge  No energy  Electrochemical gradient – both electron and concentration gradient act simultaneously on a specific ion Osmosis  Aquaporins – channels used for the passage of water  As the solute concentration increases, the water concentration decreases  Higher water concentration to lower water concentration  Lower solute concentration to higher solute concentration  The net diffusion of water is know as osmosis  Water moves by osmosis to the area of higher solute concentration Osmosis when a membrane separates unequal solutions of a penetrating solute  An equal number of water molecules have moved from side 1 to side 2 as solute molecules moved from side 2 to side 1 Osmosis when a membrane separates unequal solutions of a non penetrating solute  The side originally containing the greater solute concentration has a larger volume, having gained water Osmosis when a membrane separates pure water from a solution of a non penetrating solute  Hydrostatic (fluid) pressure – the pressure exerted by a standing or stationary fluid on an object  The hydrostatic pressure exerted by the larger volume of fluid on side 2 is greater than the hydrostatic pressure exerted on side 1  Push fluids from side 2 to side 1  Osmotic pressure of a solution is a measure of the tendency for water to move into that solution because of its relative concentration  Hydrostatic pressure matches the osmotic pressure Tonicity  Is the effect the solution has on cell volume  Tonicity of the solution is determined by its concentration of non penetrating solutes  Isotonic solution has the same concentration of ono penetrating solutes as normal body cells do, there is no net movement, so volume remains constant  Hypotpnic solution – a solution with a below normal concentration of non penetrating solutes, and a higher concentration of water. Water enters the cell by osmosis o Swell  Hypertonic solution – solution with an above normal concentration of non penetrating solutes, lower concentration of water, the cells shrink o Lose water by osmosis Assisted Membrane Transport  Carrier mediated transport for transfer of small, water-soluble substances  Vesicular transport for movement of large molecules and multi molecular particles Carrier mediated transport  Span the thickness of the plasma membrane  Reverse shape so that specific binding sites can be alternately exposed  Carrier mediated transport  Three important characteristics that determine the kind and amount of material that can be transferred across the membrane: specificity, saturation, and competition  Specificity o Specialized to transport a specific substance o Cysteinuria – involving defective cysteine carriers in the kidney membranes  Saturation o A limited number of carrier binding sites are available o Limit to the number of substances a carrier can transport in a given time o Transport maximum (Tm) o The more substance available for transport the more will be transported o When TM is reached the carrier is saturated  Competition o Closely related compounds may complete for the same carrier o When a carrier can transport two closely related substances, the presence of both diminishes the rate of transfer for either Active or passive transport  Facilitated diffusion – no energy needed o Uses a carrier to facilitate the transfer of a particular substance across the membrane, from high to low concentration o Passive o Simple diffusion o Glucose into cells  Active diffusion – energy needed o Requires the carrier to expend energy to transfer against a concentration gradient, from an area of lower concentration to higher concentration o Uptake of iodine by thyroid o Energy in the form of ATP o The change in carrier shape is accompanied by dephosphorylation - the phosphate group detaches fro the carrier o Removal of phosphate reduce the affinity of the binding site for the passenger, so the passenger is released on the high concentration side o Pumps – active transport mechanisms, that require energy o Hydrogen ion pump NA+-K+ pump  Transfer of two different passengers  ATPase pump  Transports sodium ions out of the cell and pickd up potassium ions from the outside  Splitting of ATP through ATPase activity and the subsequent phosphorylation of the carrier on the intracellular side increases the carrier’s affinity for Na+ and induces a change in carrier shape, leading to the drop off of Na+ on the exterior  This pump moved 3 Na+ out of the cell for every 2 K+ it pumps in  This pump plays 3 important roles o Establishes Na+ and K+ concentration gradients across the plasma membrane of all cells o Helps regulate cell volume by controlling the concentration of solutes inside the cell o Energy used to run this pump also indirectly serves as the energy source for the co-transport of glucose and amino acids across intestinal and kidney cells Secondary active transport  Intestinal and kidney cells actively transport glucose and amino acids by moving them uphill from low to high concentration  Energy is not directly supplied to the carrier  The carries that transport glucose against its concentration gradient form the lumens of the intestine and kidneys are distinct from the glucose facilitated diffusion carriers  The luminal carries in intestinal and kidney cells are co-transport carriers in that they have two binding sites  On for Na+ and one fro the nutrient molecule  More Na+ is preset in the lumen than inside the cells because the energy requiring Na+-K+ pump transports Na+ out of the cell at the basolateral membrane  Keeping the intracellular Na+ concentration low  Primary active transport – energy is required in the entire process, nut it is not directly required to run the pump  It uses secondhand energy stored in the form of an ion concentration gradient to move the co-transported molecule uphill  Na+ must be pumped out to maintain the electrical and osmotic integrity of the cell Vesicular transport  Requires energy Endocytosis  The plasma membrane surrounds the substance to be ingested  Then fuses over the surface pinching off a membrane enclosed vesicle so that the engulfed material is trapped within the cell  3 forms of endocytosis: pinocytosis, receptor-mediated endocytosis, and phagocytosis  Once inside the cell, the engulfed vesicle has two possible destinies o Lysosomes fuse with the vesicle to degrade and release its contents into the intracellular fluid o The endocytosis vesicle bypasses the lysosomes and travels to the opposite side of the cell, where it releases its contents by exocytosis  Pinocytosis o Cell drinking o Non selective uptake of the surrounding fluid o A small droplet of extracellular fluid is internalized o The plasma membrane dips inward, forming a pouch that contains a small bit of ECF o The plasma membrane then seals at the surface of the pouch, trapping the contents in a small intracellular endocytotic vesicle o Dynamin – a protein molecule responsible for pinching off an endocytotic vesicle o Forms a ring that warp around and wring the neck of the pouch  Receptor mediated endocytosis o Highly selective o Import specific large molecules o Triggered by the binding of a specific molecule to a surface membrane receptor o Causes the plasma membrane at that site to sink in, then seal at the surface, trapping the protein inside the cell o Cholesterol complexes, vitamin B12, insulin, and iron are examples  Phagocytosis o Cell eating o Large multi molecular particles are internalized o Extends surface projections known as pseudopods that completely surround or engulf the particle and trap it within an internalized vesicle o A lysosome fuses with the membrane of the internalized vesicle and releases its hydrolytic enzymes into the vesicle Exocytosis  Membrane enclosed vesicle formed within the cell fuses with the plasma membrane  Then opens up and releases its contents to the outside  Materials packaged for export by the endoplasmic reticulum and Golgi complex are externalized by exocytosis  Serves two different purposes o Secreting large polar molecules o Enables the call to add specific components to the membrane Secretory vesicles  Each different surface protein marker serves as a specific docking marker  Each vesicle can dock and unload only at the appropriate docking markers  Secretory vesicles – which contain proteins to be secreted, bud off from the Golgi stacks  Secretory proteins remain stored within vesicle until the cell is stimulated by a specific gland  Secretion  Before budding off from the outermost Golgi sac, the portion of the Golgi membrane that will be used to enclose the secretory vesicle becomes coated with a layer of specific proteins from the cytosol  These proteins serve three important functions o Recognition markers for the reaction and attraction of specific molecules, proteins contain a unique sequence of amino acids known as sorting signal o Coat proteins from the cytosol bind with another specific protein facing the outer surface of the membrane, causes the surface membrane of the Golgi sac to curve and form a dome shaped bud around the captured cargo o After budding off, the vesicle sheds its coat proteins. This exposes docking markers, know as v-SNAREs (secretory membrane) can link in a lock and key fashion with a t-SNARE (plasma membrane), found only on the targeted membrane  Contents of the secretory vesicles never come into contact with the cytosol  Through exocytosis and endocytosis, portions of the membrane are constantly being restored, retrieved, and recycled Chapter 3 - The Central Nervous System  Central nervous system  Peripheral nervous system  Communication Membrane Potential  Membrane potential or are polarized electrically  Allows for cellular communication in nervous tissue and muscle Separation of opposite charges  Membrane potential – separation of charges across the membrane or to a difference in the relative number of cations (+) and anions (-) inside the cell and outside the cell  Work is performed to separate opposite charges after they have come together  When they have been separated, the electrical force of attraction between them can be harnessed to perform work when the charges are permitted to come together again  Potential is measured in units of volts  Multivolt (mV) 1 mV = 1/1000 volt  Neutral membrane – equal number of positive and negative charges on both sides  Membrane potential refers to the difference in + and – charges along the thin layer of ICF and ECF membrane  The grater number of charges separated the larger the potential Concentration and permeability of ions  Cells of excitable tissue – nerve and muscle cells  Produce rapid change in their membrane potential  These serve as electrical signals  Resting membrane potential – not producing electrical signals  Ions responsible for the generation of the resting membrane potential are Na+, K+, and anions  Na+ is in grater concentration in the ECF and K+ is in much higher concentration in the ICF  These are maintained by the Na+-K+ pumps a the expense of energy  Anions are only found inside the cell  They are synthesized from amino acids transported into the cell, and remain inside the cell  More easy for K+ to get through the membrane  At resting potential in a nerve cell, the membrane is about 50 to 75 times more permeable to K+ as to Na+  The concentration gradient for K+ will always be outward and the concentration gradient for Na+ will always be inward  Because the Na+-K+ pump maintains a higher concentration of K+ inside the cell and a higher concentration of Na+ outside the cell  K+ and Na+ are both cations, the electrical gradient for both these ions will always be towards the negatively charged side of the membrane Effect of the Na+-K+ pump on membrane potential  Pumps 3 Na+ out for every 2 K+ in  This generates a membrane potential with the outside becoming more positive than the inside  Passive diffusion of K+ and Na+ down concentration gradient Effect of the movement of potassium alone on membrane potential  More positive charges outside  Negative charges left inside  Two opposing forces would now be acting on K+: the concentration gradient tending K+ out of the ell and the electrical gradient tending to move these same ions into the cell  The concentration gradient would be stronger than the electrical gradient so net movement of K+ out of the cell would continue and membrane potential would increase  Inward electrical gradient would continue to increase in strength  K+ equilibrium potential – a large concentration gradient would still exist, but no more net movement of K+ (-90mV) Effect of movement of sodium alone on membrane potential  Move this ion into the ell  Build up of positive charges inside of the membrane  Na+ equilibrium potential would be +60 mV  Inside of the cell would be positive Concurrent potassium and sodium effects on membrane potential  The greater the permeability of the plasma membrane for a given ion, the greater is the tendency for the ion to drive the membrane potential toward the ion’s own equilibrium potential  K+ passes through more readily than Na+  K+ influences the resting membrane potential more than Na+  K+ acting alone would establish an equilibrium potential of -90mV  The membrane is somewhat permeable to Na+, however, some Na+ enters the cell in a limited attempt to reach its equilibrium potential  This neutralizes some of the potential produced by K+ alone Nerve and Muscle  Nerve and muscle cells have developed a specialized use for this membrane potential  Electrical signals  The constant membrane potential that sexists when a nerve or muscle cell is not displaying rapid changed in potential is referred to as the resting potential  Nerve and muscle cells are considered excitable tissues  They change their resting potential to produce electrical signals  Nerve cells use these signals to communicate  Muscle cells use these signals to initiate movements Depolarization and Hyperpolarization  Polarization o Charges are separated across the plasma membrane o Membrane has potential o Anytime the value of the membrane potential is other than 0mV, in either a positive or negative direction, the membrane is in a state of polarization o The magnitude of the potential is directly proportional to the number of positive and negative charges separated by the membrane and that the sign of the potential always designates whether excess positive or excess negative charges are present on the inside of the membrane o At resting potential the membrane is polarized at -70mV in a typical neuron  Depolarization o A reduction in the magnitude of the negative membrane potential o The membrane becomes less polarized than at resting potential o Membrane potential moves closer to 0mV, becoming less negative o Fewer charges are separated than at resting potential o Depolarization is a movement in the positive direction, or upward on the recording device  Repolarization o The membrane returns to resting potential after being depolarized o Movement in the negative direction, or downward on the recording device  Hyperpolarization o Increase in the magnitude of the negative membrane potential o The membrane becomes more polarized than at resting potential o The membrane moves even farther from 0 mV, becoming more negative o More charges are separated than at resting potential o Movement in the negative direction, or downward on the recording device  On the recording device, during a depolarization, when the inside becomes less negative than at resting potential, this decrease in the magnitude is represented as an upward deflection  During hyperpolarization, when the inside becomes more negative than at resting potential, this increase in magnitude of the potential is represented by a downward deflection Electrical signals and ion movement  If the net inward flow of positively charged ions increases compared with the resting state, the membrane becomes depolarized, less negative inside  If the net outward flow of positively charged ions increases compared with the resting state, the membrane becomes hyperpolarized, more negative inside  Triggered event o Change in the electrical field in the vicinity of an excitable membrane o Interaction of a chemical messenger with a surface receptor on a nerve or muscle cell membrane o Stimulus, such as sound wakes stimulating nerve cells in the ear o Spontaneous change of potential caused by inherent imbalances in the leak pump cycle  Charges can cross the membrane only through channels specific to them  Membrane channels may be either leak channels or gated channels  Leaked channels o Open all the time o Unregulated leakage of their chosen ion across the membrane  Gated channels o Have gates that can alternately be open or closed o The opening and closing of gates results from a change in the 3 dimensional conformation of the protein that forms the gated channel o There are 4 kinds of gated channels o Voltage gated channels – open or close in response to changes in membrane potential o Chemically gated channels – change conformation in response to binding of a specific chemical messenger o Mechanically gated channels – respond to stretching or other mechanical deformations o Thermally gated channels – respond to local changes in temperature  There are two basic forms of electrical signals o Graded potentials – short distance signals o Action potentials – long distances Graded potential  Local changes in membrane potential  For example, membrane potential can change from -70mV to -60mV (a 10 mV graded potential) Triggering events  In most cases, these are chemically gated or mechanically gated channels  Most commonly, gated Na+ channels open, leading to the inward movement of Na+ down its concentration and electrical gradients  Depolarization – the graded potential – is confined to this small, specialized region of the total plasma membrane  The stronger the triggering event, the more gated channels that open, the grater the positive charge entering the cell, and the larger the depolarizing graded potential at the point of origin  The longer the duration of the triggering even, the longer the duration of the graded potential Graded potentials and passive currents  When a graded potential occurs locally in a nerve or muscle cell membrane, the remainder of the membrane is still at resting potential  The temporary depolarized region is called an active area  Inside the cell, the active area is relatively more positive than the neighboring inactive areas that are still at resting potential  Outside the cell, the active area is relatively less positive than these adjacent area  Because of this difference in electrical charges, passive flow between the active and adjacent resting regions on both the inside and outside of the membrane begins  Any flow of electrical charges is called a current  Direction of current flow is always in the direction in which the positive charges are moving  Ion movements is occurring along the membrane between regions next to each other on the same side of the membrane  At the adjacent site, the inside is more positive and the outside it less positive  Current spreads in both directions away from the initial site of the potential change  Resistance is the hindrance to electrical charge movement  The greater the difference in potential, the greater the current flow  The lower the resistance, the greater the current flow  Conductors have low resistance, providing little hindrance to current flow  Insulators have high resistance and greater hinder movement of charge Graded potentials and current loss  Current is lost across the plasma membrane as charge carrying ions leak through the un-insulated parts of the membrane – open channels  Magnitude of the local current progressively diminishes with increasing distance from the initial site or origin  The magnitude of the graded potential continues to decrease the farther it moves away from the initial active area  Spread of a graded potential is decremental  Local currents dies out within a few millimeters from the initial site of change in potential  Following are graded potentials o Post synaptic potentials o Receptor potentials o End plate potentials o Pacemaker potentials o Slow wave potentials  Graded potentials can initiate action potentials Action Potentials  Brief rapid large 100mV changes in membrane potential  Which the potential actually reverse 
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