Renal system

  1. Na reabsorption
    • active process
    • 80% energy requirements for reabsorption
  2. Na reabsorption in proximal tubule
    • crosses luminal membrane through co-transport with glucose, vitamins, amino acids
    • crosses basolateral membrane through Na/K ATPase pumps
    • glucose etc crosses through facilitated diffusion
    • simple diffusion into capillary
  3. renal threshold
    maximal plasma concentration of any organic nutrients before they begin to appear in the urine- spill over
  4. Na reabsorption in the ascending loop of Henle
    • coupled to K and Cl in luminal membrane
    • uses K/Na ATPase pump in the basolateral membrane
    • simple diffusion into capillary
  5. Na reabsorption in the distal tubule
    • coupled to Cl in the luminal membrane
    • uses K/Na ATPase pump in basolateral membrane
    • simple diffusion into capillary
  6. Na reabsorption in the Collecting duct
    passive channels in the luminal membrane
  7. Mechanisms for passive water reabsorption
    paracellular route
    • coupled to sodium reabsorption, has to happen before water can move
    • paracellular is in between epithelial cells, uses tight junctions
    • microenvironments created from K/Na ATPase pumps , they have a higher osmolarity
    • only in proximal tubule and descending loop of Henle
  8. mechanisms of passive water reabsorption
    transcellular route
    • coupled to NA reabsorption
    • through epithelial cells, uses osmotic gradient btw luminal space and ISP
    • requires aquaporins in luminal membrane that are created by ADH
    • aquaporins are always available in the basolateral membrane
  9. Passive Chlorine reabsorption
    • coupled to Na reabsorption, uses electrical gradient
    • Na creates positive electrical gradient in the micro-environments
    • Cl is drawn to the positive charge and is able to passively move across the luminal membrane
  10. substances that dont get reabsorbed
    • waste products, except urea
    • phenols, creatinine, nitrogen-containing wastes
  11. reabsorption in distal tubule and collecting duct
    • hormonal regulation
    • depends on secretion of ADH, aldosterone
  12. H+ secretion in the proximal tubule
    • uses H+ and Na anti-porter, Na moves out of lumen into ISP
    • H+ moves into lumen from capillary
    • important part of acid-base balance
  13. H+ secretion in collecting duct/ loop of Henle
    • use process of facilitated diffusion, ATPase pump in basolateral membrane and luminal membrane
    • passive protein carrier
  14. K reabsorption in proximal tubule
    • passive diffusion, similar to Cl and urea
    • uses osmotic gradient
    • unregulated
  15. K secretion in distal tubule and collecting duct
    • active process, regulated
    • simple diffusion across capillary, uses K/Na ATPase pump in basolateral membrane, both must be present for this pump to work
    • uses K channels in luminal membrane
    • promoted by aldosterone- enhances luminal transport mechanisms for Na, opens more channels to allow more K secretion
  16. isotonic urine
    • 300 mOsm
    • 1ml/min
  17. descending loop permeability
    • permeable to water
    • impermeable to Na
  18. ascending loop permeability
    • permeable to Na- actively pumped out
    • impermeable to water
  19. osmolarity of urine at distal tubule
    • 100 mOsm no matter our hydration status
    • concentration happens in collecting duct
  20. stimulator for ADH secretion
    • plasma osmolarity
    • higher osmolarity= more ADH secretion
  21. Mechanism of Action of ADH
    • enters blood stream, diffuses into ISP,
    • binds to receptors on the basolateral membrane
    • uses 2nd messenger to stimulate exocytosis of vesicles containing aquaporins
    • aquaporins are inserted into luminal membrane so water can move into tubule- gradient must be present
  22. sensors for Na levels
    baroreceptors, through sensation of arterial blood pressure via sensation of plasma blood volume
  23. Aortic arch and Carotid sinus baroreceptors
    short term sensors, signal the onset of changes but adapt to sustained changes in BP
  24. Renal baroreceptors
    • sense long term changes in BP
    • located in granular cells in afferent arteriole
    • sense BP and general perfusion in arteriole
  25. Renal baroreceptors MOA
    • sense decrease in BP, which is decrease in plasma volume
    • they release renin which is the rate limiting step in the production of angiotensin I, released from the granular cells
    • angio I then is converted to Angio II in the lungs and is able to affect BP
  26. effects of Angiotensin II
    • -acts on adrenal cortex to stimulate aldosterone release: regulates Na reabsorption at distal tubule and collecting duct
    • -potent vasoconstrictor for both renal and systemic arteries, slows down overall GFR
    • - reduces GFR by enhancing autoregulation, threshold decreases
    • - enhances Na reabsorption by stimulating Na/H exchangers in proximal tubule
    • - stimulates thirst and release of ADH to increase water absorption
  27. actions of Aortic and carotid baroreceptors
    • raise sympathetic stimulation to kidneys in 2 main places
    • -stimulate renal nerve to cause vasoconstriction of afferent arteriole, drop in GFR before angiotensin II takes over
    • juxtaglomerular apparatus- triggers release of renin from granular cells before renal baroreceptors kick in
    • SNS stimulation directly stimulates hypothalamus to release ADH
  28. results from a drop in BP
    • immediately sensed by aortic and carotid baroreceptors
    • causes release of renin, ADH due to increased sympathetic stimulation
    • after a while the renal baroreceptors kick in and exert their effects
  29. osmoreceptors
    • sense changes in plasma osmolarity, not CSF osmolarity
    • central osmoreceptors are most important- SFO and OVLT, circumventricular organs
    • they affect the level of thirst and renal conservation of water
  30. results of increase in plasma osmolarity
    • less water in blood than solutes
    • SFO and OVLT will sense rise and fire action potentials that lead to an increase in ADH secretion
    • creates increased water reabsorption at the distal tubule and collecting duct
    • this can create change in water levels alone, without affecting Na levels
    • increase in ADH is linear with increase in osmolarity
  31. factors that affect Plasma ADH and osmolarity
    • rate of ADH breakdown: metabolized by liver, disease will cause decreased breakdown
    • pain, fear, trauma: significant activation of sympathetic nervous system will increase ADH secretion
    • alcohol consumption: decreases plasma ADH, dehydrating effect of alcohol
  32. 3 pressures involved in GFR
    • capillary BP: pushing pressure coming from glomerular capillaries, promotes ultrafiltration, driving force for filtration, changeable
    • plasma colloid osmotic pressure: exerted by proteins that cant pass barrier, pulling pressure working against filtration
    • BC hydrostatic pressure: what moves into tubule, opposes filtration, small but positive net filtration pressure
  33. autoregulation: results of rise in BP
    • capillary BP will rise, GFR will increase, flow through distal tubule will increase and this is sensed by the macula densa cells in the distal tubule,
    • they tell the granular cells in the afferent arteriole to release vasomediators to vasoconstrict vessels to bring the GFR back to normal
  34. control mechanism 2 for GFR
    • extrinsic sympathetic control: goal is to alter GFR, to override autoregulation
    • affects smooth muscle of the afferent and efferent arterioles, NE is released and binds to alpha adrenergic receptors to cause vasoconstriction and reduce capillary BP and decrease GFR
  35. purpose of capillary bulk flow
    • to regulate distribution of ECF between plasma and interstitial space
    • includes intravascular space and interstitial space
    • completely passive process, distribution depends on sum of forces
  36. ultrafiltration
    fluid moving from intravascular to interstitial space
  37. reapsorption
    fluid moving from interstitial to the intravascular space
  38. hydrostatic pressure
    • pushing pressure, pushes out from wherever it originates from
    • pressure exerted by fluid, found in both compartments
  39. interstitial hydrostatic pressure
    will promote reabsorption, significant but not changing pressure
  40. intravascular hydrostatic pressure
    • same as capillary blood pressure
    • similar pushing force, promotes ultrafiltration
    • significant and can change, due to precapillary sphincters
    • direction of bulk flow is determined by capillary blood pressure
  41. Oncotic pressure
    • osmotic pressure exerted by proteins b/c they can cross capillary wall,
    • pulling pressure, needs fluid to balance the amount of proteins
  42. plasma oncotic pressure
    • from inside the intravascular space, from plasma proteins that are inside the capillary and they cant get out,
    • albumin levels are the strongest predictor of this pressure
    • promotes reabsorption, helps to maintain plasma volume
  43. interstitial oncotic pressure
    promotes ultrafiltration, under most circumstances this is nearly 0, or approaching 0 because albumin is not designed to get out of vasculature to exert pressure
  44. tubular maxiumum
    maximal rate of absorption in the proximal tubule
Card Set
Renal system
Physio final