Glomerular Filtration & Renal Blood flow Flashcards Preview

CVPR: Renal > Glomerular Filtration & Renal Blood flow > Flashcards

Flashcards in Glomerular Filtration & Renal Blood flow Deck (14)
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1

Basic functional anatomy of filtration apparatus of nephron

  • glomerulus = structures involved in filtration
  • filtration occurs @ capillary loops ==> Bowman's capsule of tubule
  • arterioles adjacent to capillary bed = act as valves to control blood flow to kidney & regulate GFR

2

Granular cell characteristics

  • subset of smooth muscle @ afferent arteriole
  • part of juxtaglomerular apparatus
  • secrete renin

3

Structural basis of ultrafiltration

  1. filtrate passes through gomerular capullary endothelium
    1. "fenestrated" epithelium = large holes; plasma passes easily through but RBCs do not
    2. not a major contributor to filtration
  2. Basal lamina
    1. secreted by both endothelium & epithelium
    2. composed of mucoproteins; negatively charged
    3. contributes to filtration
  3. Podocytes = sheet of tubular epithelial cells
    1. rounded cells w/"feet" projected towards endothelial layer
    2. "feet" intertwine ==> slit membranes ==> molecular sieve

4

Forces that impact filtration

  • pressure differences across filtration membrane
    • Pgc = hydrostatic pressure w/in glomerular capillaries (drives filtration)
    • Pt = "backpressure" from narrow Bowman's capsule (opposes filtration)
  • Osmotic forces
    • πgc = "colloid osmotic pressure" = large, unfiltred protein concentration rises w/in glomerular capillaries (opposes filtration)

5

GFR (starling equation) = 

  • = K (Pgc - Pt - πgc)
    • K = represents constant resistance of membrane to flow

6

Net filtration pressure (NFP) & values = 

  • = Pgc - Pt - πgc
  • ="starling forces"
  •  Pgc = 46mmHg
  • Pt = 10mmHg
  • πgc = 30mmHg
  • NFP = 6mmHg

7

K (in GRF equation) definition

  • "total hydraulic conductivity" ==> amount of fluid to flow across glomerulus per unit time per unit pressure
  • K = pA
    • p=specific hydraulic conductivity
    • A=total surface area of glomeruli w/in kidneys
    • A = ~1 m2

8

GFR regulation and homeostasis

  • relatively constant in healthy ppl
  • filtration process = nonspecific ==> changes in GFR generally not a good mechanism for maintaining ECF conditions
  • changes in p (specific conductivity) ==> changes in GFR

9

Regulation of Pgc

  • Pgc = ~1/2*MAP
  • regulation is important b/c if Pgc changed in proportion to MAP ==> overwhelm kidneys/filtration might go to zero
  • Pgc regulated via autoregulation

10

Characteristics of autoregulation

  • helps maintain GFR constancy
  • occurs via myogenic mechanism ==> MAP changes ==> smooth muscles cells w/in arteriole constrict/dilate to keep the downstream capillarly blood flow constant
  • afferent arteriole = regulating valve ==> maintains Pgc constant ==> GFR remains constant
  • works best between 75-150mmHG (MAP), but some residual error as MAP increases

11

GFR changes in (severe, chronic) hypovolemia

  • hypovolemia ==> increased peripheral resistance ==> shunting to vital organs
  • kidneys aim to preserve GFR while decreasing RBF
  • GFR maintained via coordinate constriction of afferent and efferent arterioles
    • afferent constriction ==> decreased RBF, but decreases Pgc
    • efferent constriction ==> flow diverter ==> restores Pgc & further decreases RBF (via increased resistance)

12

Stimulation of glomerular hypovolemic response

  • long-lasting decline in MAP ==> baroreceptor reflex ==> increase in renal sympathetic nerve activity ==> synapses @ afferent and efferent arterioles ==> arteriole muscle contraction
  • stimulation of afferent arteriole ==> renin release
  • intrarenal baroreceptors on granular cells detect reduced pressure ==> increase renin

13

Filtration equilibrium definition

  • NFP reaches 0 at some point before plasma exits glomerular capillary 
  • ==> "double hit" of decreased NFP (due to hypovolemia) + decreased effective area for filtration

14

Role of renal prostaglandins in hypovolemic response

  • renal prostaglandins produced by renal interstitial cells @ kindey medulla between renal pyramids
  • secreted in response to AgII ==> local dilatory effect @ renal arterioles
  • help maintain adequate RBF by blunting AgII <== prevent ischemic injury to renal tubular cells
  • selective for afferent arteriole ==> tends to restore GFR