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Physiology of Cells

Physiology of Cells. Passive Transport. Diffusion Tendency of small particles to spread out evenly within a given space Occurs down a concentration gradient until equilibrium is reached Measurable difference between one area to another

raymond-stephens
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Physiology of Cells

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  1. Physiology of Cells

  2. Passive Transport • Diffusion • Tendency of small particles to spread out evenly within a given space • Occurs down a concentration gradient until equilibrium is reached • Measurable difference between one area to another • Diffusion or permeability dependent upon presence of specified channels • Selectively permeable – channels open and close based on cell’s needs

  3. Diffusion

  4. Passive Transport 2. Dialysis (fig 4-4, pg. 94) • Selectively permeable membrane separates smaller and larger particles

  5. Passive Transport 3. Osmosis (fig 4-5, pg. 95) • Diffusion of water through a selectively permeable membrane

  6. Osmotic Pressure • Osmotic pressure – pressure that develops in a solution as a result of osmosis • Important concept for maintaining homeostasis • Isotonic – two fluids have the same osmotic pressure • Hypotonic – lower concentration of solute outside of the cell (ECF) • Hypertonic – higher concentration of solute outside of cell (ECF)

  7. Effects of Osmosis on a Cell

  8. Passive Transport 4. Facilitated Transport • (also carrier-mediated passive transport) • Movement of a molecule is facilitated by a carrier mechanism in the cell membrane • Still requires concentration gradient

  9. Passive Transport 5. Filtration • Passing of water and permeable solutes through a membrane by the force of hydrostatic pressure • Hydrostatic pressure: force or weight of a fluid pushing against a surface • Occurs down a hydrostatic pressure gradient • Most often associated with movement across a sheet of cells (ex: capillaries)

  10. Active Transport • Carrier-mediate process • Moves molecules “uphill” (against concentration gradients) • Ex: Sodium-potassium pump • Operates in all human cells

  11. Sodium-Potassium Pump • Transports Na+ out of the cell and K+ into the cell • Requires energy (sodium-potassium ATPase) – made in mitochondria • 3 Na+ bind on the intracellular side and are exchanged for 2 K+ from the ECF

  12. Sodium-Potassium Pump

  13. Endocytosis • Receptors in the plasma membrane bind to molecules in the ECF • Cytoskeleton pulls a portion of the membrane inward, creating a pocket • Edges of the “pocket” fuse forming a vesicle • Vesicle is pulled inside the cell by the cytoskeleton • Vesicle fuses with the membrane walls of a lysosome

  14. Exocytosis Process by which large molecules (proteins) exit the cell • Wastes/proteins enclosed by a membrane vesicle • Cytoskeleton moves vesicle to plasma membrane • Fuses with membrane & releases contents to ECF

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