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IVMS-Interactions Between Cells and the Extracellular Environment
 

IVMS-Interactions Between Cells and the Extracellular Environment

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IVMS-Interactions Between Cells and the Extracellular Environment

IVMS-Interactions Between Cells and the Extracellular Environment

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    IVMS-Interactions Between Cells and the Extracellular Environment IVMS-Interactions Between Cells and the Extracellular Environment Presentation Transcript

    • Interactions Between Cells and the Extracellular Environment Compiled and Presented by Marc Imhotep Cray, M.D. Basic Medical Sciences Professor Companion Notes http://www.slideshare.net/drimhotep/ivmsoverview-of-cell-biology
    • Extracellular Environment Includes all constituents of the body located outside the cell. Body fluids are divided into 2 compartments:  Intracellular compartment:  67% of total body H20. Extracellular compartment:  33% total body H20.  20% of ECF is blood plasma.  80% is interstitial fluid contained in gel-like matrix. 2
    • Extracellular Matrix Consists of collagen, elastin and gel-like ground substance.  Interstitial fluid exists in the hydrated gel of the ground substance.  Ground substance:  Complex organization of molecules chemically linked to extracellular protein fibers of collagen and elastin, and carbohydrates that cover the outside of the plasma membrane.  Collagen and elastin:  Provide structural strength to connective tissue.  Gel:  Composed of glycoproteins and proteoglycans which have a high content of bound H20 molecules.  Integrins are glycoproteins that serve as adhesion molecules between cells and the extracellular matrix. 3
    • Categories of Transport Acrossthe Plasma Membrane Cell membrane is selectively  May also be categorized permeable to some molecules and ions. by their energy  Not permeable to proteins, requirements: nucleic acids, and other  Passive transport: molecules.  Net movement down a Mechanisms to transport concentration gradient. molecules and ions through Does not require the cell membrane:  metabolic energy  Carrier mediated transport: (ATP). Facilitated diffusion and Active transport:   active transport.  Non-carrier mediated  Net movement against a transport. concentration gradient.  Diffusion and osmosis.  Requires ATP. 4
    • Diffusion Molecules/ions are in constant state of random motion due to their thermal energy.  Eliminates a concentration gradient and distributes the molecules uniformly. Physical process that occurs whenever there is a concentration difference across the membrane and the membrane is permeable to the diffusing substance. 5
    • Diffusion Through PlasmaMembrane Cell membrane is permeable to:  Non-polar molecules (02).  Lipid soluble molecules (steroids).  Small polar covalent bonds (C02).  H20 (small size, lack charge). Cell membrane impermeable to:  Large polar molecules (glucose).  Charged inorganic ions (Na+). 6
    • Rate of Diffusion Speed at which diffusion occurs.  Dependent upon:  The magnitude of concentration gradient.  Driving force of diffusion.  Permeability of the membrane.  Neuronal plasma membrane 20 x more permeable to K+ than Na+.  Temperature.  Higher temperature, faster diffusion rate.  Surface area of the membrane.  Microvilli increase surface area. 7
    • Osmosis Net diffusion of H20 across a selectively permeable membrane. Movement of H20 from a high[H20] to lower [H20] until equilibrium is reached. 2 requirements for osmosis:  Must be difference in [solute] on the 2 sides of the membrane.  Membrane must be impermeable to the solute. Osmotically active solutes:  Solutes that cannot pass freely through the membrane. 8
    • Effects of Osmosis H20 moves by osmosis into the lower [H20] until equilibrium is reached (270 g/l glucose). Osmosis ceases when concentrations are equal on both sides of the membrane. 9
    • Osmotic Pressure The force that would have to be exerted to prevent osmosis.  The greater the [solute] of solution, the > the osmotic pressure.  Indicates how strongly the solution “draws” H20 into it by osmosis. 10
    • Molarity and Molality One-molar solution:  1 mole of solute dissolved in H20 to = 1 liter.  Exact amount of H20 is not specified. Ratio of solute to H20 critical to osmosis.  More desirable to use molality (1.0 m). One-molal solution:  1 mole of solute is dissolved in 1 kg H20. Osmolality (Osm):  Total molality of a solution. Freezing point depression:  Measure of the osmolality.  1 mole of solute depresses freezing point of H20 by –1.86oC.  Plasma freezes at –0.56oC = 0.3 Osm or 300 mOsm. 11
    • Effects of Ionization on Osmotic Pressure NaCl ionizes when dissolved in H20. Forms 1 mole of Na+ and 1 mole of Cl-, thus has a concentration of 2 Osm. Glucose when dissolved in H20 forms 1 mole, thus has a concentration of 1 Osm. 12
    • Tonicity The effect of a solution  Hypotonic: on the osmotic  Osmotically active solutes movement of H20. in a lower osmolality and Isotonic: osmotic pressure than  Equal tension to plasma. plasma.  RBCs will not gain or  RBC will hemolyse. lose H20.  Hypertonic: .  Osmotically active solutes  RBC will crenate. in a higher osmolality and osmotic pressure than plasma 13
    • Regulation of Blood Osmolality Maintained in narrow range by regulatory mechanisms. If a person is dehydrated:  Osmoreceptors stimulate hypothalamus:  ADH released.  Thirst increased. Negative feedback loop. 14
    • Carrier-Mediated Transport Molecules that are too large and polar to diffuse are transported across plasma membrane by protein carriers. Characteristics of protein carriers:  Specificity:  Interact with specific molecule only.  Competition:  Molecules with similar chemical structures compete for carrier site.  Saturation:  Tm (transport maximum):  Carrier sites have become saturated. 15
    • Facilitated Diffusion Passive:  ATP not needed.  Powered by thermal energy of diffusing molecules.  Involves transport of substance through plasma membrane down concentration gradient by carrier proteins.  Transport carriers for glucose designated as GLUT. 16
    • Primary Active Transport Hydrolysis of ATP directly required for the function of the carriers. Molecule or ion binds to “recognition site” on one side of carrier protein. Binding stimulates phosphorylation (breakdown of ATP) of carrier protein. Carrier protein undergoes conformational change.  Hinge-like motion releases transported molecules to opposite side of membrane. 17
    • Na+/K+ Pump Carrier protein is also an ATP enzyme that converts ATP to ADP and Pi.  Actively extrudes 3 Na+ and transports 2 K+ inward against concentration gradient. Steep gradient serves 4 functions:  Provides energy for “coupled transport” of other molecules.  Regulates resting calorie expenditure and BMR.  Involvement in electrochemical impulses.  Promotes osmotic flow. 18
    • Secondary Active Transport Coupled transport. Energy needed for “uphill” movement obtained from “downhill” transport of Na+. Hydrolysis of ATP by Na+/K+ pump required indirectly to maintain [Na+] gradient. 19
    • Secondary Active Transport Cotransport (symport):  Molecule or ion moving in the same direction as Na+. Countertransport (antiport):  Molecule or ion moving in the opposite direction of Na+. Glucose transport is an example of:  Cotransport.  Primary active transport.  Facilitated diffusion. 20
    • Transport Across EpithelialMembranes  Absorption: Transport of digestion In order for a  products across the molecule or ion to intestinal epithelium into the blood. move from the  Reabsorption: external  Transport of molecules out of the urinary filtrate back environment into into the blood. Transcellular transport: the blood, it must  Moves material through the first pass through an  cytoplasm of the epithelial cells. epithelial  Paracellular transport: membrane.  Diffusion and osmosis through the tiny spaces between epithelial cells. 21
    • Bulk Transport Movement of many large molecules, that cannot be transported by carriers, at the same time. Exocytosis:  Fusion of the membrane-bound vesicles that contains cellular products with the plasma membrane. Endocytosis:  Exocytosis in reverse.  Specific molecules can be taken into the cell because of the interaction of the molecule and protein receptor. 22
    • Membrane Potential Difference in charge across the membrane. Cellular proteins and phosphate groups are negatively charged at cytoplasmic pH.  These anions attract positively charged cations from ECF that can diffuse through the membrane pores. 23
    • Membrane Potential (continued) Membrane more permeable to K+ than Na+.  Concentration gradients for Na+ and K+.  K+ accumulates within cell also due to electrical attraction.  Na+/ K+ATPase pump 3 Na+ out for 2 K+ in. Unequal distribution of charges between the inside and outside of the cell, causes each cell to act as a tiny battery. 24
    • Equilibrium Potentials Theoretical voltage produced across the membrane if only 1 ion could diffuse through the membrane. If membrane only permeable to K+, K+ diffuses until [K+] is at equilibrium.  Force of electrical attraction and diffusion are = and opposite. At equilibrium, inside of the cell membrane would have a higher [negative charges] than the outside. Potential difference:  Magnitude of difference in charge on the 2 sides of the membrane. 25
    • Nernst Equation Allows theoretical membrane potential to be calculated for particular ion.  Membrane potential that would exactly balance the diffusion gradient and prevent the net movement of a particular ion.  Value depends on the ratio of [ion] on the 2 sides of the membrane. Ex = 61 log [Xo] z [Xi] Equilibrium potential for K+ = - 90 mV. Equilibrium potential for Na+ = + 60 mV. 26
    • Resting Membrane Potential Resting membrane potential is less than Ek because some Na+ can also enter the cell. The slow rate of Na+ efflux is accompanied by slow rate of K+ influx. Depends upon 2 factors:  Ratio of the concentrations of each ion on the 2 sides of the plasma membrane.  Specific permeability of membrane to each different ion. Resting membrane potential of most cells ranges from - 65 to – 85 mV. 27
    • Cell Signaling How cells communicate with each other. Gap junctions:  Signal can directly travel from 1 cell to the next through fused membrane channels. Paracrine signaling:  Cells within an organ secrete regulatory molecules that diffuse through the extracellular matrix to nearby target cells. Synaptic signaling:  Means by which neurons regulate their target cells. Endocrine signaling:  Cells of endocrine glands secrete hormones into ECF. For a target cell to respond to a hormone, NT, or paracrine regulator; it must have specific receptor proteins for these molecules. 28
    • Cellular Transport Diffusion, Dialysis and Osmosis Tutorial by RM Chute Osmosis - Examples Colorada State University Osmosis by Terry Brown Interactive Cellular Transport by Rodney F. Boyer Hypotonic, Isotonic, Hypertonic by June B. Steinberg Osmosis McGraw-Hill Companies, inc Symport, Anitport, Uniport by University of Wisconsin Facilitated Diffusion by University of Wisconsin Passive and Active Transport from Northland Community and Technical College The Plasma Membrane Dr JA Miyan at Department of Biomolecular Sciences, UMIST, UK Endocytosis of an LDL EarthLink Osmosis (thistle tube) 29
    • Cellular Structure and Function Comparison of Prokaryote, Animal and Plant Cells by Rodney F. Boyer Flash animations of Biological Processes by John L. Giannini Organize It by Leif Saul Stem Cells Sumanas Inc. Membrane Structure Tutorial Various Cellular Animations University of Alberta Cellular Receptor Animations University of Oklahoma Cell Tutorial from "Cells Alive!" Simple cell by Terry Brown Kinesin - Molecular Motor Sinauer Associates Inc., W. H. Freeman Co. and Sumanas Inc. Kinesin Movie RPI Cellular Animations by Donald F. Slish Flagella and Cilia from Northland Community and Technical College 30