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Renal and Urology > renal physiology 3 > Flashcards

renal physiology 3 Flashcards

1
Q

renal corpuscle

A

glomerulus and bowmans capsule

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2
Q

what are glomerulus

A

just a group of fenestrated capillaries

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3
Q

what are fenestrated capillaries

A

capillaries which have hole

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4
Q

what do fenestrations not allow through

A

any formed elements (i.e. red blood cells, white blood cells)

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5
Q

berries to filtrations

A
  • capillary endothelium
  • negatively charged basement membrane
  • slit processes of podocytes (glomerular epithelium)
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6
Q

capillary endothelium is a barrier to

A

red blood cells

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7
Q

basement membrane is

A

negatively charged so it repels negatively charged plasma proteins but allows positiveky charged proteins to pass through

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8
Q

slit processes of podocytes are a barrier to

A

plasma proteins

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9
Q

what is allowed to pass through into bowmans capsule

A

different electrolytes, water, glucose, amino acids, lipids and small proteins

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10
Q

what do mesangial cells do

A

phagocytose any macro-molecules which get tuck between podocyte for processes

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11
Q

net filtration pressure are the forces

A

pushing things out of the glomeruli minus the pressure of the forces pushing things into the glomeruli

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12
Q

forces that comprise net filtration pressure

A
  • glomerular hydrostatic pressure
  • colloid osmotic pressure
  • bowman capsular hydrostatic pressure
  • bowmans capsular oncotic pressure
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13
Q

glomerular hydrostatic pressure

A

is the pressure in the glomerulus pushing plasma proteins out of the glomerulus into bowmans space

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14
Q

value of normal glomerular hydrostatic pressure

A

55mmHg

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15
Q

colloid osmotic pressure

A

pressure created by albumin which tries to stops fluid passing into bowmans space

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16
Q

value of colloid osmotic pressure

A

30mmHg

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17
Q

bowmans capsular hydrostatic pressure

A

exerts a pressure which pushes plasma components from the bowmans space back into the glomerulus

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18
Q

value of bowmans capsular hydrostatic pressure

A

15mmHg

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19
Q

bowmans capsulat oncotic pressure

A

would be the thoertcial pressure prevent fluid retuning to the glomerulus if there were any plasma proteins in bowmans space but there is none

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20
Q

value of bowmans capsule oncotic pressure

A

0mmHg

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21
Q

calculation of net filtration pressure

A

55+0- (30+15)= 10mmHg si the pressure favouring filtration

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22
Q

net filtration pressure is directly proportional to

A

the glomerular filtration rate (i.e. if the gloemrualr filtration rate increases eh net filtration rate will also increase)

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23
Q

startling forces

A

are the balanc elf hydrostatic pressure and osmotic forces

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24
Q

what is glomerular filtration rate

A

the rate at which protein free plasma is filtered from the glomeruli into bowmans capsule

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25
Q

normal GFR

A

125mls/min

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26
Q

GFR equals

A

Kf x net filtration rate

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27
Q

Kf

A

is the filtration co-efficiecnt i.e. how honey the glomerular membrane is

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28
Q

the major determinant of GFR

A

is the glomerual hydrostatic pressure

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29
Q

glomerular filtration rate also depends on

A
  1. the surface area of the glomerulus

2. permeability of the glomerulus

30
Q

increase in the surface area or permeability of the glomerulus

A

increases the glomerular filtration rate

31
Q

surface area and permeability are collectively known as the

A

Kf which is the filtration co-efficient

32
Q

glomerular filtration rate =

A

Net filtration pressure x the filtration co-efficient

33
Q

Clinical correlations: glomerular hydrostatic pressure is directly dependant on

A

systemic blood pressure

  • if systemic blood pressure increases then there is an increase in the glomeruarl hydrostatic pressure therefore GFR increases
  • if systemic blood pressure falls then there is a decrease in glomerular hydrostatic pressure and the GFR falls
34
Q

clinical correlations: colloid osmotic pressure is dependant on

A

the amount of proteins in the plasma

  • if there are too many proteins in the plasma i.e. in multiple myeloma the colloid osmotic pressure will increase and the glomerular filtration rate will decrease
  • if there are not enough proteins in the plasma the colloid osmotic pressure falls i.e. in severely burned patients and the GFR increases
35
Q

clinical correlations: bowmans capsular hydrostatic pressure

A

renal calculi increase the capsular hydrostatic pressure as it is causing an obstruction

36
Q

Regulation of renal blood flow and glomerular filtration rate is achieved via

A

extrinsic regulation and auto-regualtion

37
Q

extrinsic regulation of the glomerular filtration rate

A

sympathetic control via the baroreceptor reflex

38
Q

auto-regulation of the glomerular filtration rate

A
  • myogenic mechanism

- tubuloglomerualr feedback mechanism

39
Q

the myogenic mechanism and the tubuloglomerular mechanism are

A

both within the kidney and require no extrinsic input

40
Q

is systemic blood pressure is high

A

then the pressure of the blood entering the afferent arteriole is high which would be bad as it would cause excessive elevation of the glomerular hydrostatic pressure causes excessive amounts of filtration causing polyuria and even damage to to the glomerular filtration membrane, therefore, out body has a mechanism to deal with this because the afferent articles have specialised mechanoreceptors within its smooth muscle which responds to stretch, when stretched it contracts the arteriole to reduce blood flowing through the afferent arteriole which reduces the glomerular hydrostatic pressure in order to reduce glomerular filtration rate known as the MYOGENIC MECHANISM

41
Q

the opposite happens if there is low systemic blood pressure

A

then the hydrostatic pressure of the glomeruli falls which cusaes reduced production of urine which can cause oliguria or anuria which can cause renal failure, therefore, no stretch of the smooth muscle does not cause the afferent arteriole to contract but rather to dilate which increases the blood flowing through the glomerulus to increase the glomerular filtration rate

42
Q

tubuloglomerular feedback mechanism in the scenario of high glomerular filtration rate

A

high glomerular filtration rate means too much filtrate is being formed especially NaCl which cannot all get re-absorbed in the proximal convoluted tubule, so greater than normal amounts get to the loop of henle

  • the macula densa cells are chemoreceptors so they sense the chemical concentration of the filtrate
  • in the distal convoluted tubule there are Na+/Cl- symporters in the manual dense cells so a lot of sodium and chloride get re-absorbed
43
Q

the excessive re-absorption of sodium in the macula densa cells causes

A

the voltage to increase causing the release of ATP from the macula densa cells which then gets converted to adenosine, the adenosine binds to a receptor activating a G protein pathway on the mesangial cells causing the release of calcium from the smooth endoplasmic reticulum from the mesangial cells which is in turn connected to the junta-glomerualr cells, so calcium flows into the juxta-glomerualr cells binding to granules containing renin and inhibits the release of renin resulting in inhibition of the RAAS SYSTEM, mesangial cells are also connected to smooth muscle cells of the afferent arteriole causing them to contract causing constriction of the afferent arteriole reducing the EGFR via the myogenic mechanism

44
Q

if there is a low glomerular filtration rate what affect does this have on the tubuloglomerualr feedback mechanism?

A

if there is a low GFR then there is reduced NaCl in the filtrate and none of the above can occur, there is no calcium binding to renin vesicles so RENIN CAN BE RELEASED AND THE RAAS SYSTEM CAN BE ACTIVATED,

45
Q

extrinsic control of the glomerular filtration rate

A

synmptathic control via the baroreceptor reflex usually occurs when systolic blood pressure falls below 80mmHg

46
Q

how does the body sense a fall in systemic blood pressure

A

baroreceptors within the carrots sinus on the glossopharyngeal and vagus nerve activate the synampthetic nervous system in response to low blood pressure causing the release noradrenaline which binds to alpha-1-adrenergic receptors causing vasoconstriction of the afferent arteriole which causing a reduction in the glomerular filtration rate, this might be the opposite to what you think should happen but at this low a blood pressure your body is trying to save your life not your kidneys, in order to maintain systemic blood pressure the body is sacrificing the kidneys

47
Q

however, changes in systemic blood pressure don’t always

A

cause changes in the glomerular filtration rate which can be explained using the myogenic and reflex and the tubuloglomerualr reflex

48
Q

plasma clearance is a measure of

A

how quickly the kidneys can clear the blood of a substance

49
Q

plasma clearance is the

A

volume of plasma cleared of a particular substance per minute

50
Q

each substance handled by the kidneys will have its

A

own particular plasma clearance

51
Q

clearance of substance X=

A

rate of excretion of substance X/ PLASMA CONCENTRATION OF SUBSTANCE X

52
Q

clearance of inulin

A
  • freely filtered at the glomerulus
  • enters the urine purely via filtration and is not re-absorbed nor secreted
  • not metabolised by the kidney
  • not toxic
  • amount of inulin filtered per unit time= amount of inunlin excreted per unit time
53
Q

what is used to detect clearance clinically

A

creatinine rather than inulin

54
Q

inulin clearance is equal to the

A

glomerular filtration rate

55
Q

for substances which are filtered but completely re-absorbed

A

clearance is 0

56
Q

substances which are not filtered or not secreted

A

clearance is 0

57
Q

for substances which are filtered, partially re-absorbed but not secreted

A

clearance is less than the glomerular filtration rate (e.g urea)

58
Q

for substances which are filtered, not re-absorbed but are secreted

A

clearance is greater than the glomerular filtration rate (i.e. hydrogen ions)

59
Q

if clearance is less than the GFR

A

the the substance is re-asbored

60
Q

if clearance is equal to the GFR then the

A

substance is neither secreted nor-reabsorbed

61
Q

if clearance is greater than the GFR then the

A

substance is secreted

62
Q

para-amino hippuric acid

A

exogenous organic anion used clinically to measure plasma flow
- PAH is freely filtered at the glomerulus, secreted into the tubule but not -reabosorbed and is completely cleared from the plasma

63
Q

clearance of inulin

A

125ml/min however, requires a constant infusion of inulin which is why creatinine is used instead

64
Q

clearance of creatinine

A

around 125ml/min creatinine is a breakdown product of muscles and is produced at a near constant rate, it is freely filtered and not re-absorbed but a small amount is secreted so it may slightly overestimate clearance (GFR) but is more convenient than inulin

65
Q

any substance used as a clearance marker should be

A
  • non-toxic
  • not metabolised
  • easy to measure
66
Q

GFR markers should be

A

freely filtered and not secreted or re-absorbed

67
Q

a renal plasma flow marker

A

should be filtered and completely secreted

68
Q

filtration fraction

A

is the fraction of plasma flowing through the glomeruli that is filtered through the tubules

69
Q

filtration fraction

A

GFR/ plasma flow

70
Q

ie filtration fraction is

A

125/ 650= 20% therefore, 20% of blood entering the glomerulus is filtered the remaining 80% moves onto the peri-tubular capillaries

Renal and Urology (51 decks)

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