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Membrane Transport

Membrane Transport. Membrane Transport. method by which substances move through the cell membrane cells bathed by interstitial fluid cells must take nutrients from this fluid to remain healthy reject unnecessary substances. Selective Permeability.

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Membrane Transport

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  1. Membrane Transport

  2. Membrane Transport • method by which substances move through the cell membrane • cells bathed by interstitial fluid • cells must take nutrients from this fluid to remain healthy • reject unnecessary substances

  3. Selective Permeability • the ability of the plasma membrane to regulate entry and exit of materials • Movement of materials through plasma membrane can be: - passive - active

  4. Passive Processes • simple diffusion • osmosis • filtration • facilitated diffusion

  5. Passive Processes - Simple Diffusion • random movement of particles (ions and molecules) • particles move along a concentration gradient - a region of higher concentration to a region of lower concentration.

  6. Passive Processes - Osmosis • diffusion of solvent -water diffuses from a region of higher solvent concentration toward a region of lower solvent concentration through a selectively permeable membrane • Example: - the small intestines absorb water from digested food by osmosis

  7. Osmotic Pressure • the pressure required to prevent the net movement of water from one solution to another when the solutions are separated by a membrane permeable only to water • the pressure needed to stop the flow of water across the membrane

  8. Tonicity • normal firmness or functional readiness in body tissues or organs • maintain the shape of red blood cells; they must be bathed in an isotonic solution. - normal saline solution is isotonic for red blood cells

  9. Isotonic Solution(iso = same) • same concentration of water and particles (solute and solutes) as in the cells • when RBC’s are in 0.9% NaCl solution water molecules enter and exit the cells at equal rates (5% glucose) • RBC’s maintain their normal shape and volume

  10. Hypotonic Solution (hypo = less than) • lower concentration of solutes than in cells • higher concentration of water • when RBC’s are placed in distilled H2O, water molecules enter the cell faster than they leave • RBC’s will swell and burst (hemolysis)

  11. Hypertonic Solution(hyper = greater than) • higher concentration of solutes • lower concentration of water than in the cells • if RBC’s are placed in hypertonic solution more water leaves the cells than enters - cells will shrivel and die (crenation)

  12. Passive Processes - Filtration • solvent and solute move across a membrane due to gravity or water pressure (hydrostatic) • Example: - in kidneys blood pressure forces water and small creatinine (a waste product) molecules through a plasma membrane

  13. Filtration (cont.) • filtered liquid enters kidneys • large molecules such as proteins remain in blood • smaller harmful molecules can then be eliminated in the urine

  14. Passive Processes -Facilitated Diffusion • lipid-insoluble molecules and molecules too large to diffuse through membrane or ion channels are carried through membrane by transporter (carrier) proteins • Example: - glucose

  15. Facilitated Diffusion (cont.) • after glucose bonds to transporter on the outside of the membrane, the transporter changes shape • glucose passes through membrane and is released inside the cell

  16. Active Transport • requires the use of energy from ATP to move substances across the membrane • substances move from areas of lesser concentration to areas of greater concentration • opposite direction of diffusion • movement occurs against a concentration gradient

  17. Na+ (Sodium) K+ (Potassium) H+ (Hydrogen) Ca + 2 (Calcium) I- (Iodine) Cl- (Chlorine) amino acids monosaccharides Actively Transported Substances:

  18. Active Transport (cont.) • Two Types: - primary active transport - secondary active transport

  19. Primary Active Transport: The Sodium Pump • ATP energy directly moves substances across membrane • sodium pump - most prevalent - maintains a low concentration of (Na+) ions in the cytosol - also moves (K+) ions into cells • in nerve and muscle cells

  20. The Sodium Pump • Na+ ions are more abundant outside the cell • they are constantly diffusing into the cell, (their area of lesser concentration) • not needed in such abundance • sodium pumps must return Na+ ions to outside (their presence will bring about unwanted nerve impulses or muscle contractions)

  21. Secondary Active Transport • energy stored in ion gradients moves substances across the membrane • indirectly uses energy from splitting ATP

  22. Endocytosis • Processes that bring large substances into cells: - phagocytosis - pinocytosis - receptor-mediated endocytosis

  23. Phagocytosis • projections on outside of plasma membrane, called pseudopods, flow around large particles (bacteria, debris) engulfing and bringing them into cell • once surrounded, membrane sac is formed (phagocytic vesicle) • vesicle enters cytoplasm • material in vesicle is digested by enzyme produced by lysosome

  24. Pinocytosis • membrane folds or sinks beneath liquid to be digested forming pinocytic vesicle • pinocytic vesicle allows liquid to flow inward trapping the liquid • vesicle pinches off or detaches from membrane into cell interior

  25. Receptor-Mediated Endocytosis • similar process to pinocytosis • substances bind to receptors on the plasma membrane causing a folding of the membrane and the formation of an endocytic vesicle • highly selective • cells take up specific molecules or particles

  26. Exocytosis • membrane enclosed sacs (secretory vesicles) form inside cell - fuse with plasma membrane - release contents into extracellular fluid - important in nerve cells - secrete digestive enzymes or protein hormones such as insulin • requires ATP

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