IVMS-Interactions Between Cells and the Extracellular Environment


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IVMS-Interactions Between Cells and the Extracellular Environment

  1. 1. 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
  2. 2. 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
  3. 3. 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
  4. 4. 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
  5. 5. 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
  6. 6. 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
  7. 7. 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
  8. 8. 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
  9. 9. 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
  10. 10. 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
  11. 11. 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
  12. 12. 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
  13. 13. 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
  14. 14. 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
  15. 15. 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
  16. 16. 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
  17. 17. 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
  18. 18. 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
  19. 19. 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
  20. 20. 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
  21. 21. 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
  22. 22. 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
  23. 23. 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
  24. 24. 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
  25. 25. 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
  26. 26. 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
  27. 27. 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
  28. 28. 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
  29. 29. 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
  30. 30. 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