Physiology - Renal Topic #2

  1. Kidney Structure
  2. Nephron Types:
    • cortical: (short) make dilute urine (fish that secrete ammonia)
    • juxtamedullary: (long) make concentrated urine
  3. Renal Processes
    • 1- filtration
    • 2- reabsorption (into blood)
    • 3- secretion (into tubule)
    • 4- excrition (end result of process)
  4. Filtration
    • occurs in: glomerulus/ bowmans capsule (covers glomerulus)
    • podocytes: contain gaps for movement of plasma content
    • capsule damage allows RBCs, and proteins into urine (blood in urine=sign of capsule damage)
    • 20% blood plasma filtered per round
    • kidney recieves 25% of CO
    • amount of fluid filtered = 180
    • urinary output =1.5
  5. Glomerular Filtration Rate (GFR)
    • = rate of plasma filtration
    • changes in GFR often change urine output
    • low GFR generally indicates renal failiure
  6. Filtration Forces
    • PROMOTED by: blood pressure
    • OPPOSED by:
    • osmotic (oncotic) pressure - more proteins re absorbed in blood
    • tubule pressure (fluid already in capsule)
  7. Regulation of GFR
    • GFR autoregulation =maintenance of constant GFR over a wide range of BP
    • ruquires altering vascular resistance
    • sense by: high blood pressure opening stretch sensitive ion channels in afferent arterioles
    • response: constriction thus lower blood flow

    • flow sensed by: macula densa
    • response: paracrine hormones constrict afferent arteriole
    • sympathetic innervation:
    • reduces GFR
    • occurs during hemorrage
    • mechanism: afferent arteriole vaso constriction
  10. Controlling Permeability
    • mesangial cells surround glomerular capillaries and contract to secrete inflammatory mediators to cause podocytes to swell thus blocking surface of capillaries and decreasing glomerular permeability
    • contract when stimulated by - angiotensin 2
  11. MORE-----Measuring GFR
    • measured by CLEARANCE of a filtered substance which is not reabsorbed, metabolized or secreted
    • clearance: the volume of filtered fluid that had all solutes removeed from it
    • characteristics of test substance for filtration

    • insulin clearance used experimentally to find GFR
    • creatinine more practical - a muscle metabolism byproduct, fairly constant plasma level
  12. MORE-----Calculating GFR
    • filtration rate x Plasma conc = Urine conc x Urine Volume
    • aka (mass filtered) = (mass excreted)

    • GFR =
    • c = m/v
  13. MORE-----filtration
    • filtered fluid volume returns to the plasma without the solute (the volume is cleared)
    • V and GFR are RATES (usually measured over 24 hr)
  14. Measuring Renal Plasma Flow
    • PAH is totally cleared so its used to measure RPF
    • measured by agents that are both filtered and secretec but not absorbed
    • total clearance: no agent remains in renal vein
    • RPFxP(pah)=U(pah)xV/t
    • or RPF=[U(pah)xV/t] P(pah)
  15. Renal Blood Flow
    • calculation of renal blood flow depends on the hematocrit (% RBCs in blood):
    • RBF =RPF/1-HTC (hematocrit)
Card Set
Physiology - Renal Topic #2
Topic #2 – Glomerular Filtration