Physiology of Cells by hcj


									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
  –   Diffusion or permeability dependent
      upon presence of specified channels
  –   Selectively permeable – channels open
      and close based on cell’s needs
         Passive Transport
2. Dialysis (fig 4-4, pg. 94)
  – Selectively permeable membrane
    separates smaller and larger particles
        Passive Transport
3. Osmosis (fig 4-5, pg. 95)
  – Diffusion of water through a selectively
    permeable membrane
         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
• Hypotonic – lower concentration of solute
  outside of the cell (ECF)
• Hypertonic – higher concentration of solute
  outside of cell (ECF)
Effects of Osmosis on a Cell
          Passive Transport
4. Facilitated Transport
  – (also carrier-mediated
    passive transport)
  – Movement of a
    molecule is facilitated
    by a carrier
    mechanism in the cell
  – Still requires
         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
  – Most often associated with movement
    across a sheet of cells (ex: capillaries)
         Active Transport
• Carrier-mediate process
• Moves molecules “uphill” (against
  concentration gradients)
• Ex: Sodium-potassium pump
  – Operates in all human cells
   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
Sodium-Potassium Pump
•   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 is pulled inside the cell by the
•   Vesicle fuses with the membrane walls of
    a lysosome
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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