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Renal/GU > 04: Tubular Reabsorption > Flashcards

04: Tubular Reabsorption Flashcards

1
Q

Hormones controlling glomerular hemodynamics

A

Angiotensin II (AII), norepinephrine (NE), atrial natriuretic factor (ANF)

  • EC volume depletion: ↑AII, NE
  • EC volume overload: ↑ANF
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2
Q

Regulation of ∆P, ∆π by ANF

A
  • Stretching in heart releases ANF –> dilates afferent arteriole –> ↑RBF –> ↑∆P (transmitting systemic pressures), ↓∆π (delivering fresh blood so that filtration equilibrium is never reached) –> ↑GFR
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3
Q

Regulation of ∆P, ∆π by AII

A
  • Angiotensinogen secreted by liver and converted into angiotensin I by renin (kidney), then angiotensin II by ACE (capillaries-lung)
  • Constricts efferent arteriole –> ↓RBF –> ↑∆P but ↓∆π –> no change in GFR (but secondary effects)
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4
Q

Regulation of ∆P, ∆π by NE

A
  • Constricts both afferent and efferent arterioles –> no change in ∆P but RBF is diminishedk –> ↑∆π –> ↓GFR
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5
Q

Filtration Fraction

A

Filration fraction = GFR/RPF

The proportion of the fluid reaching the kidneys which passes into the renal tubules; nl ~20%

nl RPF = 667ml/min

  1. NE: ↓GFR, ↓RPF = no change in FF
  2. ANF: ↑GFR, ↑↑RPF = ↓FF or no change
  3. AII: no change GFR, ↓RPF = ↑FF
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6
Q

Proximal tubule

A
  • Reabsorbs:
    • 67% NaCl and H2O
    • most bicarbonate
    • all glucose and AAs
    • filtered proteins (via receptor called megalin)
  • Secretes small organic ions
    • cAMP
    • aspirin
    • penicillin
    • morphine
  • ​In presence of angiotensin II, higher osmotic pressure in peritubular capillaries results in increased water reabsorption.
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7
Q

Peritubular capillaries

A

Tiny blood vessels that travel alongside nephrons allowing reabsorption and secretion between blood and the inner lumen of the nephron

PTR = Kf x (osmotic - hydrostatic)

  • FF determines osmotic pressure
  • Fluid exiting is isotonic
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8
Q

Proximal tubule sodium reabsorption

A
  • Na/H exchanger in apical membrane
  • Na/solute co-transporter (glucose, AA) in basal membrane
  • AII increases the reabsorption of sodium
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9
Q

Proximal tubule glucose filtration & excretion

A
  • Filtered = Pgluc x GFR; 2800 mg/L x 200 L/d
  • Excreted = Ugluc x V; if Pgluc < 2800 mg/L = 0
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10
Q

Na-K-ATPase

A
  • Basolateral membrane of renal tubular cells
  • Inhibited by cardiac glycosides digoxin and ouabain
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11
Q

Organic anions secreted by proximal tubules

A
  • Endogenous: cAMP, prostaglandins, bile salts, hippurates, oxalate & urate
  • Drugs: penicillin, probenecid, ASA

Secreted via organic anion transporter (OAT)

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12
Q

Loop of Henle

A
  • Reabsorb Na, Cl, K, no water
  • ↓ luminal osmolality but ↑interstitium (unstirred layer of high osmolarity that surrounds medullary tubules)
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13
Q

Sodium handling in TALH

A
  • Sodium potassium cotransporter channel (NKCC) reabsorbs from tubule.
  • Renal outer medullary potassium channel (ROMK) secretes into tubule.
  • Chloride channel (CLC-Kb)
  • Associated protein barttin
  • Mutations in any of the above result in Bartter’s Syndrome with a phenotype similar to use of diuretic furosemide.
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14
Q

Sodium absorption in distal tubule

A
  • Thiazide-sensitive Na+-Cl- cotransporter (TSC) reabsorbs
  • Gittelman’s is defet in trafficking of TSC to the cell surface.
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15
Q

Collecting ducts

A
  • Acidify the urine
  • Reabsorb sodium
  • Secrete potassium
  • Reabsorb water
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16
Q

Principle cell

A
  • Reabsorbs final Na, secretes K
  • TJs seal paracellular space
  • Aldosterone binds mineralocorticoid receptor (MR) –> ↑opening ENaC (amiloride sensitive), ↑synthesis NaK ATPase & K channel
17
Q

Intercalated cell

A
  • Secretes H+ and generates new bicarbonate (from protein metabolism/CO2 generation)
  • Urine contains NH3 which traps secreted protons to form ammonium
  • Aldosterone binds mineralocorticoid receptor (MR) which ↑ synthesis **NaK ATPase **and H+ ATPase
18
Q

Water in the collecting duct

A

Anti-diuretic hormone (vasopressin) stimulates insertion of vesicles with aquaporin channels into apical membrane of cell –> water in dilute urine traverses cell and exits into hypertonic medulla

Renal/GU (11 decks)

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