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Renal Exam 1 > RBF and GFR > Flashcards

RBF and GFR Flashcards

1
Q
  • What are the three layers of the glomerular filtration barrier?
A
  1. Capillary endothelium
  2. Glomerular basement membrane
  3. Podocyte epithelium (+ slit processes)
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2
Q
  • Glomerular endothelium _ forms a biogel in the endothelial lumen
  • Is this positively or negatively charged
A
  • Glycolax
  • Negatively
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3
Q
  • What molecules are prominent in filtration slits to act as molecular fillers?
A
  • Actinin
  • Cadherin
  • Nephrin
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4
Q
  • What substances are freely filtered through the filtration barrier?
A
  • Water
  • Small solutes (< 20 A)
  • Concentrations equal on both sides of the membrane
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5
Q
  • What substances are not freely filtered through the filtration barrier?
A
  • Large molecules (proteins)
  • Formed elements (cells)
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6
Q
  • What charges are repelled by the glycolax membrane?
A
  • Positive (because the glycolax membrane is negative)
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7
Q
  • How do you calculate filtered load of substance x?
A
  • Filtered Load = [X]plasma x GFR
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8
Q
  • How do you calculate urinary excretion?
A

Urinary excretion=amount filtered-amount reabsorbed+ amount secreted

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9
Q
  • How do you calculate tubular reabsorption?
A

Tubular reabsorption=GFR-Urinary excretion+amount secreted

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10
Q
  • What two substances’ clearances can be used for estimating GFR?
  • Which is more favorable clinically?
A
  • Inulin
  • Creatinine
  • Creatinine-less accurate but you don’t have to infuse it (unlike inulin)
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11
Q
  • How do you calculate Clearance?
A
  • Cx= [Urine]x x V/[Plasma]x
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12
Q
  • What is a normal GFR?
A
  • 125 mL/min
  • 20% of RBF
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13
Q
  • How do you calculate filtration fraction?
  • How is filtration fraction related to oncotic pressure of the efferent arterioles?
  • How do you increase FF and efferent arteriole oncotic pressure?
  • How do you decrease FF and efferent arteriole oncotic pressure?
A
  • FF=GFR/RBF
  • As FF increases, oncotic pressure of efferent arterioles increases
    • EX: If you are increasing the GFR you are increasing the amount of fluids being filtered out of the glomerulus you are increasing glomerular capillary oncotic pressure and thus the oncotic pressure in the efferent arterioles.
    • Increase GFR or Decrease RBF
    • Decrease GFR or Increase RBF
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14
Q
  • How does the sympathetic nervous system act on the kidneys to increase blood pressure? (3 Key ways)
A
  1. Vasoconstriction of afferent arterioles (alpha 1) > efferent arterioles
  2. Increased renin release from juxtaglomerular granular cells (beta 1 adrenoreceptors)
  3. Stimulation of the Na+/K+ ATPase (via alpha one adrenergic receptors) to increase Na+ reabsorption
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15
Q
  • What are the immediate effects of sympathetic stimulation?
A
  • Stimulates renin secretion by granular cells
  • Angiotensin II exerts thirst
  • Angiotensin II restores systemic BP via Vasoconstriction
  • Angiotensin II preferentially acts on afferent arterioles
  • Stimulates Na+ reabsorpition in PCT and DCT
  • Overall systemic blood pressure is raised
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16
Q
  • What are the eventual effects of sympathetic stimulation?
A
  • Decreased urinary output
  • Decreased Na+ excretion
  • Increased water intake
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17
Q
  • What characteristics must a substance have to use its clearance value and GFR interchangeably?
A

1) Freely filtered
2) Neither secreted nor reabsorbed
3) Not synthesized, broken down, or accumulated by the kidney
4) Physiologically inert

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18
Q
  • What BUN/Creatinine ratio would be a pre-renal problem?
A
  • >20:1
  • BUN reabsorption is increased
    • EX:
      ​Hypovolemia
    • Dehydration
    • Reduced renal perfusion
    • High Protein Diet
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19
Q
  • What BUN/creatinine ratio would be a normal or post renal problem?
  • What are some examples of when this would occur?
A
  • 20:1
  • Postrenal disease
  • Obstruction of urethra
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20
Q
  • What BUN/creatinine would be a intrarenal problem?
  • What are some situations that would explain this?
A
  • <20:1
  • Renal disease (decreasing BUN reabsorption)
  • Liver diseaes, low protein diet
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21
Q
  • Why is PAH a good estimate of RPF?
  • What are some contraindications to using PAH measurements?
A
  • Freely filtered and secreted
  • Amt in plasma is approximately equal to the amount excreted
  • RPF=Clearance of PAH
  • Have to administer via IV
  • Only about 90% is actually excreted
22
Q
  • What forces favor filtration out of the glomerular capillary?
A
  • hydrostatic pressure in GC
  • oncotic pressure in BC (SHOULD BE 0)
23
Q
  • What forces favor reabsorption in the glomerular capillary?
A

GC oncotic pressure

BC hydrostatic pressure

24
Q
  • What three physical factors contribute to GFR?
  • What two of these factors are combined to create Kf (the ultrafiltration coefficient)
A
  • Hydraulic conductivity (Lp)(permeability/porosity of the fenestrated endothelium)
  • Surface area for filtration (sf)
  • Capillary ultrafiltration pressure (PUF)
  • Kf=Lp x Sf
25
Q
  • What is the equation for GFR using the three physical factors that contribute to its value?
A
  • GFR=Kf x PUF
  • PUF=PGc-Pbc-Πgc
  • Remember that Oncotic pressure in BC should be zero
26
Q
  • What type of cells can influence Sf and thus Kf?
  • How do they do so?
A
  • Glomerular mesangial cells
  • Contract to decrease the surface area of the glomerular capillary (can decrease the Kf by decreasing Sf) and thus can alter GFR
27
Q
  • How will constriction of afferent arterioles affect GFR and RPF?
  • How will this change filtration fraction?
A
  • Would decrease both GFR and RBF
  • Would not change FF
28
Q
  • What effect would efferent arteriole vasoconstriction have on GFR and RPF?
  • How would this change the filtration fraction?
  • When is an instance where you would have efferent arteriole vasoconstriction?
A
  • Increase GFR
  • Decrease RPF
  • Increase filtration fraction
  • Angiotensin II
29
Q
  • What effect would afferent arteriole vasodilation have on GFR and RBF?
  • How would this affect the filtration fraction?
A
  • Increase GFR
  • Decrease RBF
  • Increase filtration fraction
30
Q
  • What effect would efferent arteriole vasodilation have on GFR and RBF?
  • How would this affect FF?
A
  • Decrease GFR
  • Increased RBF
  • Would decrease FF
31
Q
  • The kidneys consume O2 at _ times the rate of the brain and have _ times the blood flow of the brain
  • O2 consumption is related to the high rate of _
A
  • Two, Seven
  • Na+ reabsorption
32
Q
  • What three physiological parameters that extrinsically control GFR and RBF?
  • What intrinsically controls renal hemodynamics?
A
  • Sympathetics
  • Hormones
  • Vasoactive signals
  • Autoregulation and tubuloglomerular feedback=extrinsic
33
Q
  • Sympathetic Nervous system activate _ receptors located primarily in the _ arterioles and cause _
  • This causes what changes in GFR and RBF?
A
  • Alpha 1 adrenergic, afferent, vasoconstriction
  • Decreases both GFR and RBF
34
Q
  • Glomerulotubular balance _ reabsorption rate when GFR rises
  • What is this mechanism?
A
  • Glomerulotubular balance increases reabsorption rate when GFR increases
  • Flow rate and reabsorptive rate are linked
  • Changes in pressure in efferent arteriole nad peritubular capillaries (higher oncotic pressure)-more plasma water and solutes are being filtered and more will thus be reabsorbed
35
Q
  • _ maintains RBF and GFR within narrow limits across wide ranges of blood pressures
  • How does it do so?
  • What is the range?*
A
  • Autoregulation
  • EX: Increase in pressure and increased resistance
    • Local reflex
      • Between vascular smooth muscle cells
    • Physiological feedback via the juxtaglomerular apparatus
  • 80-170 mmHg
36
Q
  • Explain the local myogenic feedback reflex
A
  • Period of high blood pressure
  • Smooth muscles within vessels contract
  • Ca2+ signaling (sensitive to Adenosine?-comes from macula densa signaling)
  • Afferent arteriolar constriction
  • Efferent arteriolar dilation
37
Q
  • What makes up the juxtaglomerular apparatus?
A
  • Macula densa cells
  • Juxtaglomerular cells
  • Extraglomerular mesangial cells
38
Q
  • Describe how tubuloglomerular feedback works in response to an increase in blood pressure
A
  • Increased RBF and Increased GFR
  • Increased delivery of Na+ and Cl- to macula densa
  • Increased release of vasoactive substances (EX; adenosine) from macula densa
  • These substances act to vasoconstrict the afferent arteriole (via Ca2+ signaling -*in the juxtaglomerular mesangial cells?*)
  • Decrease RBF and GFR
39
Q
  • Describe how tubuloglomerular feedback works in response to a decrease in systemic arterial pressure
A
  1. Decreased arterial pressure
  2. Decreased Glomerular hydrostatic pressure
  3. Decreased GFR
  4. Decreased delivery of Na+ to macula densa
  5. Macula densa signal juxtaglomerular cells
  6. juxtaglomerular cells secrete renin
  7. Leads to production of angiotensin II
  8. Leads to an increase in efferent arteriolar resistance
  9. Decreased delivery of Na+ to the macula densa leads to an increased release of local vasoactive NO
  10. Decrease in afferent arteriolar resistance
40
Q
  • What are some factors that increase the sensitivity of TGF?
A
  • Volume contraction
  • Adenosine
  • PGE 2
  • Thromboxane
  • Angiotensin II
41
Q
  • Factors that decrease the sensitivity of TGF?
A
  • Volume expansion
  • ANP
  • NO
  • cAMP
  • PGI 2
  • High protein diet
42
Q
  • What substances can cause afferent arteriole vasodilation?
  • How does afferent arteriole dilation affect RBF, GFR and Peritubular capillary hydrostatic pressure?
A
  • Prostaglandins, bradykinin, NO, dopamine, ANP
  • Increase RBF and GFR
  • Increase peritubular capillary hydrostatic pressure
43
Q
  • What substances can cause afferent arteriole vasoconstriction?
  • How does it affect RBF, GFR, and peritubular capillary hydrostatic pressure?
A
  • ACE inhibitors
  • Decreasing RBF and GFR
  • Decrease in peritubular capillary hydrostatic pressure
44
Q
  • What causes efferent arteriole vasodilation?
  • What affect does this have on RBF, GFR, and peritubular capillary hydrostatic pressure?
A
  • Sympathetics
  • Decrease in GFR
  • Increase in RBF
  • Increase in peritubular capillary hydrostatic pressure
45
Q
  • What substance causes efferent arteriole vasoconstriction?
  • What effects does this have on RBF, GFR, and Peritubular capillary hydrostatic pressure?
A
  • Angiotensin II
  • Increased GFR
  • Decreased RBF
  • Decreased peritubular capillary hydrostatic pressure
46
Q
A
  • Plasma creatinine and GFR are inverself proportional
  • Top graph is creatinine
  • Bottom is GFR
47
Q
A

Cystine C

Serum Cystine C

48
Q
A
  • Red line=excreted PAH
  • Green line=Secreted PAH
  • Blue line=Filtered PAH
49
Q
A
  • Renal artery
  • Afferent arteriole
  • Glomerular capillary
  • Efferent arteriole
  • Peritubular capillary
  • Intrarenal vein
  • Renal vein
50
Q

PUF Graph shown below

A
  • Favors filtration: PGC and Oncotic(BC)
  • Favors reabsorption: P(BC) and Oncotic (GC)
51
Q
  • Which line represents afferent arteriole vasoconstiction?
  • Which line represents efferent arteriole vasoconstriction?
A
  • Green
  • Red

Renal Exam 1 (7 decks)

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