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Renal > Glomerular Filtration I > Flashcards

Glomerular Filtration I Flashcards

1
Q

Which of the following is NOT a component of the glomerular permeability barrier?

a. Visceral epithelial cells (a.k.a. podocytes)
b. Glomerular basement membrane
c. Parietal epithelial cells (a.k.a. Bowman’s capsule)
d. Negatively charged glycosaminoglycans
e. Glomerular capillary endothelial cells

A

C - parietal epithelial cells of the bowman’s capsule

These cells are distinct from the epithelial cells that cover the glomerular
capillaries and are not part of the glomerular permeability barrier

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2
Q

Which of the following would tend to decrease GFR?

a. An increase in hydrostatic pressure in the glomerular capillary.
b. A decrease in oncotic pressure in the glomerular capillary.
c. A decrease in total glomerular capillary surface area.

A

c - A decrease in total glomerular capillary surface area.

This would decrease GFR

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3
Q

Which of the following statements about creatinine is FALSE?

a. Creatinine is freely filtered by the glomerulus.
b. Creatinine is neither reabsorbed nor secreted by the tubules.
c. Creatinine is a clinically useful marker of GFR.
d. Cimetidine may increase the plasma creatinine concentration.

A

b. Creatinine is neither reabsorbed nor secreted by the tubules.
Creatinine is secreted by organic cation transporters in the proximal tubule

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4
Q

Which of the following statements is most consistent with tubuloglomerular feedback?

a. increased NaCl delivery to the thick ascending limb causes increased proximal fluid reabsorption.
b. decreased NaCl delivery to the thick ascending limb causes increased proximal fluid reabsorption.
c. increased NaCl delivery to the thick ascending limb causes no change in proximal fluid reabsorption.
d. increased NaCl delivery to the thick ascending limb causes decreased glomerular filtration rate
e. increased NaCl delivery to the thick ascending limb causes increased glomerular filtration rate

A

d. d. increased NaCl delivery to the thick ascending limb causes decreased glomerular filtration rate

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5
Q

What is the approximate rate of glomerular filtration in a healthy, young individual?

a. 125 ml/hour
b. 125 ml/min
c. 60 ml/hour
d. 60 ml/min

A

B - 120 +- 25 ml/min is normal

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6
Q

Are the capillary beds of the nephron arranged in series or in parallel?

A

in series

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7
Q

The majority of nephrons are: cortical or juxtamedullary

A

cortical

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8
Q

What is a cortical nephron?

A

a nephron with glomeruli located in the cortex

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9
Q

Which type of nephron (cortical or juxtomedullary) has a short loop of henle and shared peritubular capillaries?

A

cortical

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10
Q

Which type of nephron (cortical or juxtomedullary) has the vasa recta following the loops of Henle?

A

juxtomedullary

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11
Q

Which nephron type does the majority of filtration (cortical or juxtomedullary)?

A

cortical

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12
Q

What is the role of juxtomedullary nephrons, given that they do not do the majority of filtration?

A

they establish the concentration gradients that cause excretion of concentrated urine

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13
Q

What are the four cell types of the glomerulus?

A
  1. fenestrated endothelium of the capillary loops
  2. visceral epithelial cells/podocytes
  3. parietal epithelial cells
  4. mesangial cells
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14
Q

What cells create the bowmans capsule or space?

A

the parietal epithelial cells that surround the glomerular capillary tuft

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15
Q

Which cells of the glomerular filtration system have contractile ability?

A

mesangial cells

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16
Q

What 3 barriers make up the filtration barrier in the glomerulus?

A
  1. capillary endothelial cells
  2. basement membrane
  3. podocytes
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17
Q

What size molecules is freely filtered through the glomerulus?

A

those less than 20 angstroms

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18
Q

Which plasma protein cannot be filtered due to the fact that it is a fairly large anion?

A

albumin

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19
Q

What is the glomerular basement membrane made up of?

A

type Iv and V collagen
laminin
fibronectin
anionic GAGs

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20
Q

What two parts of the glomerulus filtration barrier are coated in anionic GAGs and glycoproteins?

A

the basement mebrane (lamina rara externa/densa) and podocytes

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21
Q

Which cell in the filtration system form a slit diaphragm?

A

podocytes

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22
Q

What is the equation that determines urinary excretion rate?

A

Urinary excretion rate of a substance is equal to the rate at which the substance is filtered minus its reabsorption rate plus the rate at which it is secreted from the peritubular capillary blood into the tubules

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23
Q

What is the primary force driving glomerular filtration?

A

hydrostatic pressure gradient

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24
Q

As oncotic pressure rises along the length of the glomerular capillary, what happens to the driving force for filtration?

A

it falls to zero before reaching the efferent arteriole

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25
Q

What proportion of the renal plasma flow is filtered into bowman’s space?

A

20%

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26
Q

Is oncotic pressure the same as osmotic pressure?

A

NO. Oncotic pressure is exerted by proteins that are restricted to one side of a fenestrated vascular barrier. The general effect of oncotic pressure is to oppose filtration and to promote retention of fluid within a vascular space]

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27
Q

What are the variables affecting GFR?

A
  • intrinsic capillary wall permeability
  • surface area
  • hydrostatic pressure change
  • oncotic pressure change
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28
Q

Is there a large or small drop in hydrostatic pressure from the afferent to the efferent arteriole?

A

small

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29
Q

What generates the hydrostatic pressure in bowman’s space that can oppose filtration?

A

the tight capsule surrounding the kidney

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30
Q

Does oncotic or hydrostatic pressure increase from the afferent to the efferent arteriole?

A

oncotic pressure

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31
Q

What is the filtration fraction?

A

the ratio of GFR to renal plasma flow (GFR/RPF)

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32
Q

What mechanism can change capillary surface area? what effect does this have on GFR?

A

mesangial cell contraction

Decrease it

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33
Q

Renal artery pressure, afferent arteriole tone, and efferent arteriole tone can all modulate what factor driving GFR?

A

hydrostatic pressure gradient in the glomerular capillary

34
Q

Define autoregulation of GFR and RPF

A

renal artery pressure affects GFR, but does not do so linearly across a range of BPs

35
Q

What are the 3 major factor regulating autoregulation of GFR and RPF?

A
  1. myogenic reflex in afferent arteriole
  2. tubuloglomerular feedback
  3. AT II vasoconstriction of efferent arteriole
36
Q

What is the first line of defense to protect GFR when renal blood flow fluctuates/

A

myogenic reflex, which constricts or dilates the afferent arteriole
protects against sudden elevations in systolic pressure

37
Q

Below what mean BP does GFR and RPF begin to fall?

A

below 100 mmHg

38
Q

Define tubuloglomerular feedback

A

With high tubular flow rates, a proxy for an inappropriately high filtration rate, there is increased solute delivery to the macula densa that evokes vasoconstriction of the afferent arteriole causing glomerular filtration rate to return to normal.

39
Q

Where is the macula densa located?

A

thick ascending loop of Henle

40
Q

What is the final mediator of afferent arteriole vasoconstriction released by the macula densa in tubuloglomerular feedback?

A

adenosine

41
Q

What effect do loop diuretics have on the macula densa and tubuloglomerular feedback?

A

block feedback by interfering with NaCl reabsorption by macula densa

42
Q

What two conditions would cause the macula densa to release adenosine and vasoconstrict the afferent arteriole?

A

increased solute concentration at a constant flow rate OR increased fluid flow rate

43
Q

What are the 3 cell types that make up the JGA?

A

macula densa
extraglomerular mesangial cells
granular cells

44
Q

What kind of cells are macula densa cell?

A

specialized epithelial cells

45
Q

what are granular cells in the JGA?

A

synthesize, store and secrete renin

46
Q

Where in the JGA (which part of the nephron) are granular cells found?

A

in the wall of the afferent arteriole

47
Q

What does renin cleave?

A

angiotensinogen to angiotensin I

48
Q

What effect does angiotensin II have on Na reabsorption?

A

it increase it by stimulating proximal tubular Na/H exchange activity and constricting the efferent arteriole, which increases peritubular oncotic pressure and promotes the secretion of aldosterone

49
Q

What inhibits renin secretion? (hormone)

A

angiotensinogen II, negative feedback

50
Q

What are some whole organ stimulants of renin secretion?

A

stimulants: low Cl delivery, B1 adrenergic stimulation of granular cells
inhibitors: high Cl delivery

51
Q

What are some endocrine stimulants of renin secretion?

A

catecholamines
PTH
glucagon

52
Q

What are some endocrine inhibitors of renin secretion?

A

ATII
ANP
vasopressin

53
Q

What are some autocrine stimulants of renin secretion?

A

PGE2/PGI2

histamine

54
Q

What are some autocrine inhibitors of renin secretion?

A

adenosine and NO

55
Q

What are some cellular stimulants of renin secretion?

A

increased cAMP

decreased cytosolic Ca

56
Q

What are some cellular inhibitors of renin secretion?

A

decreased cAMP

increased cytosolic Ca

57
Q

What role does NaCl delivery to the macula densa have on tubuloglomerular feedback and renin secretion?

A

OPPOSITE effects - high NaCl = TGF, low NaCl = renin secretion

58
Q

Is TGF or renin secretion dependent on adenosine?

A

TGF

59
Q

Is TGF or renin secretion dependent on prostaglandins/COX 2?

A

renin secretion

60
Q

Define clearance.

A

Clearance of a particular substance is defined as the rate at which that substance is cleared from plasma per unit concentration.

61
Q

Conceptually, what does clearance correspond to?

A

the virtual volume of plasma that is cleared of a substance per unit time. It DOES NOT REFLECT AN ACTUAL VOLUME OF A SUBSTANCE

62
Q

As elimination rate per unit concentration of plasma goes up, what happens to clearance?

A

it goes up

63
Q

Whats the equation for clearance?

A

Cx = UxV/ Px
Cx - clearance of X
Ux and Px - urine and plasma concentrations of X
V - urine flow rate (ml/min)

64
Q

Ideally, if a substance is freely filtered across the glomerulus and excreted solely by glomerular filtration, what will be the relationship between clearance and GFR?

A

they will be equal, and GFR = UxV/ Px

65
Q

Why can inulin be used to measure GFR?

A

Measurement of GFR can be accomplished by using a biochemical marker that possesses certain characteristics:

  1. Freely filtered by the glomerulus
  2. Not reabsorbed by the tubules
  3. Not metabolized in the nephron
  4. Not secreted into the tubular lumen
  5. Not excreted by extra-renal routes
  6. Can be measured in urine and plasma

** for exposure **

66
Q

How is inulin clearance measured?

A

individual is infused with IV inulin until steady state an in put = output, then a 24 hour urine sample is collected

67
Q

What are some of the cons of using inulin to measure GFR?

A

it’s limited availability, expensive to administer and measure

68
Q

What is the main source of creatinine?

A

skeletal muscle and some meat intake

69
Q

What is creatinine production proportional to?

A

muscle mass and intact hepatic function

70
Q

Where is creatinine secreted from in the kidney?

A

proximal tubules via OCT system (can be blocked by cimetidine and trimethoprim)

71
Q

Under what conditions does urine need to be collected for creatinine clearance to be a good proxy for GFR?

A

at steady state - ie not after protein rich meals or exercise

72
Q

Normally, what should be true for creatinine excretion during 24 hours?

A

it should be constant for any urine output - if lower than expected, not all of the urine was collected

73
Q

If GFR decreases, what happens to creatinine excretion and plasma levels?

A

excretion decreases and plasma increases

74
Q

What effect does age have on creatinine excretion?

A

decreases it due to decreases in muscle mass

75
Q

What effect does renal disease have on GFR estimates using creatinine?

A

overestimates it due to secretion of creatinine

76
Q

What can be used to get an accurate GFR when there is renal disease causing creatinine secretion?

A

cimetidine or trimmethoprim (but not as good)

77
Q

What should always be true of the change in creatinine releative to the estimated GFR?

A

it should be a proportional and opposite change

78
Q

What is the Cockroft Gault formula?

A

an estimate for predicting creatinine clearance from plasma values
(140 - age) x lean body mass (kg)/ (plasma Cr (mg/dL)) x 72

79
Q

What value do you multiply the cockroft gault formula by in women?

A

0.85 due to lower average lean body weight

80
Q

what is the normal value of the cockroft gault formula?

A

95 +/2 20 ml/min women

120 +/- 25 ml/min men

Renal (28 decks)

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