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Renal Physiology Flashcards

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USMLE® Step 1 flashcards
1
Q

what are the 6 major functions of the kidney?

A

1) regulation of water and electrolyte balance
2) excretion of metabolic waste products/foreign chemicals
3) regulation of blood pressure
4) secretion of erythropoietin
5) secretion of 1,25-dihydroxyvitamin D3
6) regulation of extracellular pH

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2
Q

What are the kidneys?

A

2 retroperitoneal organs about the size of a fist (wt = 150g)

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3
Q

what is a nephron?

A

filtering units of the kidney each containing a selective filtering unit (glomerulus)

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4
Q

what percentage of volume is reabsorbed in the kidneys?

A

99%

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5
Q

what is urethritis?

A

inflammation of urethra

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6
Q

what is cystitis?

A

inflammation of bladder

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7
Q

what is pyelonephritis?

A

infection of kidney

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8
Q

what is the glomerulus?

A

highly specialized membrane for selective filtration, containing a network of capillaries between an afferent and efferent arteriole

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9
Q

what allows effective filtration at glomerulus?

A

large surface area that allows fluids and small molecules across but not protein

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10
Q

what is glomerular filtration rate? what is the normal range?

A

total movement of fluid across the glomerular membrane for all nephrons
100-125mL/min

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11
Q

What is the flow of blood through the glomerulus?

A 
afferent arteriole
glomerular capillaries (filtration site)
efferent arteriole
peritubular capillars and vasa recta
venules
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12
Q

where are the two capillary beds (glomerulus and peritubular) located in relation to one another?

A

two capillar beds in parallel

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13
Q

where is bowman’s capsule?

A

surrounding glomerulus

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14
Q

what are the 3 layer of the glomerular membrane?

A 
endothelial cells
basement membrane (basal lamina)
podocytes (foot processes)
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15
Q

describe the endothelial cells

A

perforated and have pores

contain fenestrations

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16
Q

describe the basal lamina

A

acellular

contains collagen and glycoprotein

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17
Q

describe podocytes

A

epithelial cells that encircle glomerular tuft

there are narrow slits between podocytes

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18
Q

what is the glomerular membrane sensitive to?

A

changes in BP and P sub GC

changes in Glc levels

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19
Q

what are the 3 glomerular cell types?

A

mesangial cells
macula densa
juxtaglomerular apparatus

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20
Q

what are the mesangial cells?

A

muscle cells between capillary loops that are able to contract and decrease GFR

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21
Q

what are the mesangial cells?

A

muscle cells between capillary loops that are able to contract and decrease GFR

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22
Q

where is the macula densa? what is its function?

A

located in early distal tubule and between afferent/efferent arterioles
detects changes in tubular fluid

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23
Q

what is the function of the JGA?

A

contain granule cells that secrete renin and other vasoactive chemicals

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24
Q

how are the JGA and macula densa related?

A

macula densa can detect changes in tubular fluid and tell JGA to release agents to regulate GFR accordingly (through vasoconstriction/dilation)

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25
Q

what drives filtration?

A

starling forces

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26
Q

what is P sub GC?

A

pressure in glomerular capillary

acts on bowman’s capsule

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27
Q

what is pi sub BC?

A

oncotic pressure of filtrate in Bowman’s capsule

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28
Q

what is P sub BC?

A

pressure in bowman’s capsule

acts on glomerulus

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29
Q

what is pi sub GC?

A

oncotic pressure of plasma in glomerular capillary

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30
Q

what is Kf?

A

filtration coefficient (leakiness)

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31
Q

what 2 forces favour filtration?

A

P sub GC

pi sub BC

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32
Q

what 2 forces oppose filtration?

A

P sub BC

pi sub GC

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33
Q

what is the main determinant of GFR? what happens if you increase or decrease it?

A

P sub GC

incr: GFR increases (leads to damage of glomerular membrane)
decr: GFR decreases

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34
Q

what controls P sub GC?

A

afferent and efferent arterioles

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35
Q

what controls P sub GC? what hormones are involved?

A

afferent and efferent arterioles

ang 2 and NE

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36
Q

what happens to PsubGC if you constrict afferent arteriole? efferent arteriole?

A 
aff = decr PsubGC
eff = incr PsubGC
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37
Q

what happens to PsubGC if you constrict afferent arteriole? efferent arteriole?

A 
aff = decr PsubGC
eff = incr PsubGC
38
Q

what are two intrarenal mechanisms and what is their overall function?

A

1) myogenic (generated within muscle)
2) tubuloglomerular feedback

keep RBF (renal blood flow) and GFR constant of wide range of BP

39
Q

how does myogenic mechanism keep RBF and GFR constant?

A

prevents increase in PsubGC and GFR by constricting the muscle when theres increased BP

40
Q

how does tubuloglomerular feedback help keep RBF and GFR constant?

A

tubules talk to glomerulus
macula densa detects changes in fluid flow/content in distal tubule and tells JGA to release constrictor/dilator accordingly

41
Q

how does tubuloglomerular feedback help keep RBF and GFR constant?

A

tubules talk to glomerulus
macula densa detects changes in fluid flow/content in distal tubule and tells JGA to release constrictor/dilator accordingly

42
Q

what does the myogenic and tubular glomerular feedback mechanisms do when there is an increase in RBF?

A

protect PsubGC
myogenic contstricts afferent
tubular glomerular feedback reduces flow to prevent PsubGC from going up

43
Q

what does the myogenic and tubular glomerular feedback mechanisms do when there is an increase in RBF?

A

protect PsubGC
myogenic contstricts afferent
tubular glomerular feedback reduces flow to prevent PsubGC from going up

44
Q

what 3 substances are released when there is volume depletion/low BP? what causes each release?

A

baroreceptor reflex incr NE
decr renal perfusion incr ang 2
decr BP incr ADH

45
Q

use of NE, Ang 2 and ADH may cause severe vasoconstriction. what do the kidneys do to prevent that?

A

release of vasodilatory prostaglandins

46
Q

use of NE, Ang 2 and ADH may cause severe vasoconstriction. what do the kidneys do to prevent that?

A

release of vasodilatory prostaglandins

47
Q

how are prostaglandins formed?

A

membrane phospholipids are converted to arachidonic acid
cyclooxygenase, COX1 and COX2 convert arachidonic acid to prostaglandin intermediates which go on to become prostaglandins

48
Q

how are prostaglandins formed?

A

membrane phospholipids are converted to arachidonic acid
cyclooxygenase, COX1 and COX2 convert arachidonic acid to prostaglandin intermediates which go on to become prostaglandins

49
Q

how could aspirin cause renal failure?

A

prostaglandins prevent intence constriction of afferent/efferent caused by Ang 2 and NE
aspirin can block prostaglandin and allow severe constrition

50
Q

what is creatinine?

A

natural product of muscle metabolism and constant from day to day and freely filtered (not secreted or reabsorbed)
estimates GFR

51
Q

what are 3 values to know the importance of?

A

1) creatinine clearance
2) MDRD eGFR equation to estimate GFR
3) blood urea/creatinine ratio to determine volume depletion

52
Q

what is the problem with eGFR?

A

only accurate with patients who have GFR less than 60 and have been stable for a period of time

53
Q

what can blood urea:creatinine ratio tell us?

A

early volume depletion

if over 0.07, then hypovolemia

54
Q

what is the relationship between plasma creatinine and GFR? why is this significant?

A 
inverse relationship (filtration goes down, plasma Cr goes up)
a small change in plasma Cr may reflect a large change in GFR
55
Q

what is the relationship between plasma creatinine and GFR? why is this significant?

A 
inverse relationship (filtration goes down, plasma Cr goes up)
a small change in plasma Cr may reflect a large change in GFR
56
Q

how much is reabsorbed in the proximal tubule?

A

95%

57
Q

what does the negatively charged barrier of the glomerulus do

A

repel proteins, making the filtrate protein free

58
Q

what is reabsorbed at proximal tubule?

A

water/Na (55-70%)
HCO3 (85%)
Glucose (100%)
small amount of filtered protein (95%)

59
Q

what does volume depletion do to proximal tubule? How?

A

increases reabsorption since there is a decre in water and solute
increases constriction of afferent and efferent (dec. RBF but efferent constriction corrects drop in PsubGC)
decreases plasma osmotic pressure in peritubular capillaries

60
Q

what can volume depletion do to drug/metabolites?

A

increase reabsorption which can be toxic

61
Q

what is different about the blood going to peritubular capillaries when there is volume depletion?

A

increased protein conc and increased osmolality

62
Q

what does less blood flow mean in terms of RBF?

A

greater fraction of RBF is filtered and protein is left behind in blood

63
Q

what is the equation for excretion?

A

exc = filtration - reabsorption + secretion

when reabsorption is 100%, then filtration = reabsorption

64
Q

what happens to excretion, reabsorption, filtration with increase plasma Glc?

A

filtration goes up
excretion does not go up until there is quite a big incr in plasma glc (transport maximum = Tm)
reabsoprtion goes up until certain point (Tm) is reached

65
Q

what happens to excretion, reabsorption, filtration with increase plasma Glc?

A

filtration goes up
excretion does not go up until there is quite a big incr in plasma glc (transport maximum = Tm)
reabsoprtion goes up until certain point (Tm) is reached

66
Q

what is the function of descending loop of henle?

A

reabsorbs water

increases concentration of electrolytes in filtrate

67
Q

what 2 conditions are required to pull water out from lumen of descending tubule?

A

high water permeability so water can freely pass but not ions
hypertonic interstitum causing osmotic forces to pull water from lumen

68
Q

what is the function of the ascending loop of henle?

A

Na, Ca, Cl, Mg, and Ca are reabsorbed

Water is left behind (dilutes)

69
Q

what is the function of the distal tubule?

A

Na and Ca (PTH activated) reabsorption

water left behind (dilutes)

70
Q

what is the function of collecting ducts?

A

Na reabsorbed, K secreted (as a loss)
water reabsorbed if ADH present
H+ excreted
concentrates urine

71
Q

what parts of the nephron segments are in the adrenal medulla? cortex?

A

cortex: distal tubule, proximal tubule and part of collecting duct
medulla: loop of henle, part of collecting duct

72
Q

what causes renin release?

A

decreased RA pressure, decr Na load, decr renal perfusion pressure, beta-adrenergic receptor stimulation

73
Q

what is the function of ang 2?

A 
vasoconstrictor
release aldosterone
increase thirst
increase Na appetite
increase ADH
increase NE release
74
Q

what happens when BP decreases?

A

baroreceptors increase Sym nerve activity (incr HR and contractility)
renin release leads to ang 2 formation, leading to aldosterone release and Na retention

75
Q

how does converting enzyme affect bradykinin?

A

causes it to be inactive, leading to decreased vasodilation and increased TPR

76
Q

how does converting enzyme affect bradykinin?

A

causes it to be inactive, leading to decreased vasodilation and increased TPR

77
Q

what increases aldosterone?

A

ang 2
potassium
ACTH

78
Q

what does aldosterone do?

A

incr Na reabsorption but incr K loss

incr H loss

79
Q

what does ADH do?

A

opens water channels (incr water reabsorption in collecting ducts)
vasoconstriction
thirst

80
Q

what causes ADH release?

A

incr in osmolality of plasma

decr blood volume

81
Q

what two receptors activate ADH?

A

osmoreceptors

baroreceptors

82
Q

what two receptors activate ADH?

A

osmoreceptors

baroreceptors

83
Q

what is the major prostaglandin in the kidney? what triggers PG production?

A

PGE2

NE and ang 2

84
Q

what are 3 sources of calcium?

A

GI tract
kidneys
bone

85
Q

how much caclium is reabsorbed in kidneys and where is it reabsorbed the most?

A

99%
60% proximal tubule
(distal tubule under PTH control)

86
Q

what does PTH do in GI?

A

stimulates activation of vit D to increase interstinal Ca absorption

87
Q

what does PTH do in kidneys?

A

incr calcium reabsorption in distal tubule and decr phosphate reabsorption in proxminal tubule

88
Q

what does PTH do in bone?

A

mobilizes Ca from bone to ECF

89
Q

what does Vit D do in GI?

A

incr Ca and phosphate absorption in gut

90
Q

what does Vit D do in bone?

A

incr responsiveness of bone to PTH to incr Ca mobilization

91
Q

what does Calcitonin do?

A

works primarily in bone to decr Ca movement from bone fluid to plasma and decr bone resoprtion (inhibits osteoclasts)

92
Q

what does erythropoietin do?

A

increases hemoglobulin synthesis and production of RBCs when there is hypoxia

Medical Physiology (15 decks)

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