Membrane Transport

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sbandzar
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169988
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Membrane Transport
Updated:
2012-09-10 03:27:01
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Med school
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  1. Which ions belong to the ECF and ICF? K+, Cl-, Na+, Ca2+
    • ICF = K+
    • ECF = Na+, Ca2+, Cl-
  2. What are the compositions of ECF?
    Plasma and Interstitual Fluid (IF)
  3. The difference between plasma and IF?
    Plasma proteins in plasma
  4. What is diffusion and what causes it?
    Net transport of molecules from high concentration to low concentration

    random thermal (molecular) motion of molecules in aqueous medium
  5. Diffusion occurs both ways (left to right; right to left) but net flux is ____?
    Uni-directional (towards low solute concentration)
  6. Ficks law equation? 
    J (flux) = P (permeability) x A (area of membrane) x (Ca-Cb) (concentration difference) / DeltaX (membrane thickness)

    **Some equations have DeltaX as part of P
  7. What factors affect Permeability?
    1. reflection coefficient (sigma); sigma = 1 means impermeable, sigma = 0 highly permeable 

    2. lipid solubility

    3. size and shape of diffusing molecule

    4. temperature

    5. membrane thickness
  8. In simple diffusion, how does the movement of lipid soluble molecules differ than water-soluble molecules differ?
    Lipid soluble molecules move readily across membrane (rate depends on lipid solubility)

    Water soluble molecules move through channels or pores (i.e. water via aquaporins); ions move through gated channels
  9. The function and purpose of lidocaine, dihydropyridines, and amiloride?
    Lidocaine: block voltage-gated Na+ channel to inhibit nerve action potentials

    Dihydropyridines: block Ca2+ channels regulate blood pressure and heart fxn

    Amiloride: block epithelial sodium channels (ENaC) {which bring Na into epi cell} and cause diuresis (urine production)
  10. How is facilitated diffusion similar and different from simple diffusion?
    Similar: does NOT use ATP, transfers molecule DOWN concentration gradient

    Different: uses uniporter (transport protein) to carry single molecule down gradient, can be saturated at Vmax
  11. Rate of diffusion of fascilitated diffusion (carrier-mediated diffusion) is limited by what 2 things?
    • 1. Vmax of carrier protein
    • 2. the density of carrier proteins in the membrane (# per unit area)
  12. Features of carrier-mediated diffusion (informational flashcard)
    • 1. carrier mediated diffusion takes place more rapidly than simple diffusion would occur FOR THAT SOLUTE.
    • 2. transport rate shows saturation
    • 3. membrane carrier proteins show high degree of chemical specificity for substances they bind
    • 4. comp. and non-comp. mechanisms can limit binding to carrier (i.e. drugs targeting carriers)
    • 5. can work in both directions, but always DOWN concentration gradient
    • 6. required binding and conformational change in carrier protein
  13. Is it called fac. diffusion if you use a carrier protein and expend energy?
    NO!
  14. Primary Active transport characteristics and example?
    Example: Na+/K+ ATPase pump (which is electrogenic meaning it generates electricity via pumping 3 Na+ out of cell and 2 K+ in cell).

    Uses energy, carrier protein on plasma membrane, pumps 3 Na+, 2K+ to maintain membrane potential and osmotic balance across cell membrane
  15. Why does Na+ leak into cells? Why does K+ leak into cells?
    Na+ Leak due to electro (cell is neg. charged) and chemical (moving down gradient) gradients.

    K+ leaks due to chemical gradient

    Therefore, Na+/K+ pump works to counteract leaks
  16. What is the main driving force behind most of sec. active transport?
    Na+ gradient outside cell set-up by Na/K ATPase pump
  17. Secondary active transport types?
    **in contrast to primary active transport, no ATP is used...the electrochemical gradient of moving down gradient is used to drive the transport.

    Cotransport (Symport)
    : ions move in same direction (one goes DOWN gradient, and the other goes up gradient using that energy); Same direction

    Countertransport (exchanger or antiport): ions move in opposite directions (one ion goes up gradient, the other goes down); different directions
  18. What are glycosides? 2 Examples of glycosides? How do they work?
    Glycosides (i.e. digoxin and ouabain) inhibit Na/K ATPase pump

    Glycosides block Na/K ATPase, which block the Na+/Ca2+ exchanger, controlling cardiac contractility by keeping Ca2+ intracellularly
  19. Do simple, facilitated, primary active, antiport, and symport diffusion used carrier protein, metabolic energy, Na+ gradient? What type of gradient is being overcome? What happens if Na/K ATPase is inhibited?
  20. Osmolarity?
    Concentration of osmotically active particles

    i.e.  1 mM NaCl = 2 milliosmoles, 1 mM CaCl2 = 3 milliosmoles

    **plasma contains 280 milliosmoles per liter of water
  21. Does size of solute effect osmolarity of particle?
    No
  22. Definition Isotonic, hypotonic, hypertonic, isosmotic?
    isotonic: no net movement of fluid into or out of cell

    hypotonic: lower tonicity causing net movement of fluid into a cell; cell in hypotonic soln will swell

    hypertonic: higher tonicity causing net movement of fluid out of a cell; shrivel cell

    isosmotic: equal concentrations of osmotically active particles across a semi-permeable membrane
  23. Particles that CAN cross (permebale) a semi-permeable membrane?
    Dextrose and Urea 

    **in these cases tonicity DOES NOT equal osmolarity
  24. You put a cell in 100 mmol of urea + 100 mmol CaCl2? The solution is considered?
    Isotonic because inside cell (350 mmol) and outside cell (350mmol) since urea IS permeable
  25. (information slide) Dextrose is isosmotic with plasma. When dextrose is infused into patient, it enters cells until osmolarity is equal b/w ICF and ECF. Net result =?

    Although D5W (dextrose) is isosmotic, it is a hypotonic solution when infused.
    Expansion.
  26. Manipulating ECF NaCl- 
    If plasma [NaCl] increases (i.e. sweating) or decreases (rapid drinking of water) what happens?
    1. NaCl will remain in plasma, water sweated out...ECF becomes hypertonic...cells shrink

    2. NaCl will remain, osmolarity is less in ECF...ECF is hypotonic..cells swell 
  27. Purpose of epithelial sodium channel (ENaC)?
    On the Apical side (near lumen) there is a sodium channel that simply diffuses Na into epithelial cell and on the basolateral side there is Na/K ATPase pump to transfer Na to circulation.
  28. CFTR airway fluid secretion diagram? How does a bad CFTR cause problems?
    Failure of CFTR impairs thickening of airway mucus and impaired cilia action. Airway fluid depends on balance b/w Cl- secretion (green) and ENaC Na+ absorption (red)...therefore defective CFTR decreases net water in ciliary mucus layer (water follows salt) 

  29. How do sweat glands and CFTR impairment changing sweat composition?
    Sweat usually is just water on the skin (Na+ and Cl- is reabsorbed via ENaC and CFTR). NOTE: CFTR in sweat glands is absorbing Cl- unlike in airways. But if CFTR is messed up, Cl- is also sweated out/secreted (diagnostic tool). 

    There is probably a Na+/Cl- symport on the basolateral membrane in sweat glands (check with Arsy...last slide of ppt)
  30. What is paracellular transport?
    Paracellular transport refers to the transfer of substances across an epithelium by passing through the intercellular space between the cells
  31. Which of the following is the internal env of the body?

    a) Intracell fluid

    b) Total body water

    c) plasma

    d) Plasma epithelial lumen fluid
    plasma
  32. RBCs are transferred to a solution containing 100mmol Cacl2 and 100mmol urea. How does this affect rbc volume?
    Isotonic (350; 350)

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