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My2 renal > Physiology 3: glomerular filtration and renal blood flow > Flashcards

Physiology 3: glomerular filtration and renal blood flow Flashcards

1
Q

what are the 3 glomerular filtration barriers

A

glomerular capillary endothelium –> basement membrane –> podocyte slit process

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2
Q

what is the the glomerular filtration rate (GFR)

A

rate at which protein-free plasma is filtered from the glomerulus into Bowman’s capsule

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3
Q

what is the filtration coefficient Kf

A

holey glomerular membrane

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4
Q

how do you calculate the GFR in terms of the filtration coefficient and net filtration pressure

A

GFR = Kf x net filtration pressure

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5
Q

what is the normal GFR

A

125ml/min

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6
Q

what is the major determinant of GFR and what other factor promotes filtration

A

glomerular capillary fluid pressure (glomerular BP)

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7
Q

what forces oppose filtration and why

A

glomerular capillary oncotic pressure - concentrated blood does not want to lose water via filtration /// (bowman’s hydrostatic pressure - self explanatory)

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8
Q

what is the net pressure across the glomerular capillaries and bowman’s capsule

A

10mmHg

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9
Q

describe the process in how the GFR would adjust to help compensate a fall in blood volume eg haemorrhage

A

decreased arterial BP –> detected by aortic and carotid baroreceptors –> increased sympathetics –> arteriole constriction –> afferent arteriole constricted –> decreased glomerular capillary pressure (BP) –> decreased GFR –> decreased urine

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10
Q

what extrinsic factor can regulate GFR

A

sympathetic control via baroreceptors

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11
Q

how does sympathetic activity regulate GFR

A

causes vasoconstriction of arteriole and lowers GFR (raised BP = lower GFR, lowered BP = raised GFR)

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12
Q

what 2 intrinsic factors regulate GFR

A

myogenic mechanism and tubuloglomerular feedback

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13
Q

how does the myogenic mechanism work

A

if vascular smooth muscle is stretched (increased BP) it contracts the arteriole to keep the BP constant

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14
Q

how does the tubuloglomerular apparatus work

A

juxtaglomerular apparatus where macula densa senses high NaCl in tubule and constricts afferent arteriole - this maintains the GFR despite a short term increased BP

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15
Q

what is the purpose of intrinsic regulation

A

to prevent short term BP changes affecting GFR

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16
Q

when would extrinsic control override intrinsic control

A

when a large haemorrhage occurs

17
Q

what effect does kidney stones have on GFR and why

A

decreased - causes a block downstream which increased bowman’s capsule fluid pressure so no pressure gradient for blood to enter the capsule

18
Q

what effect does diarrhoea have on GFR and why

A

decreased GFR - patient is dehydrated and plasma proteins within the blood will become more concentrated and increase the osmotic pressure of the blood which opposes filtration

19
Q

what effect does extreme burns have on GFR and why

A

increased GFR - plasma proteins are lost in the burn so concentration within blood is less and a weaker capillary oncotic pressure promotes filtration

20
Q

what does plasma clearance indicate

A

how effectively the kidneys can ‘clean’ the blood if a substance - varies for each substance

21
Q

how is plasma clearance measures

A

volume of plasma cleared of a substance per minute

22
Q

what is the equation for plasma clearance

A

rate of excretion of X/ plasma [X] = ([X]urine x Vurine) / [X]plasma

23
Q

what X clearance is a perfect marker for GFR

A

inulin

24
Q

why is creatine used over inulin as a marker of GFR

A

it occurs naturally in the body

25
Q

name a substance which is filtered and completely reabsorbed and not secreted - what is it’s clearance

A

glucose - clearance = 0

26
Q

name a substance which is filtered and partly reabsorbed and not secreted - what is it’s clearance

A

urea - clearance < GFR

27
Q

name a substance which is filtered and not reabsorbed and completely secreted - what is it’s clearance

A

H+ - clearance > GFR

28
Q

what is renal plasma flow

A

blood delivered to the kidneys per unit time

29
Q

what is used to measure renal plasma flow (RPF)

A

the clearance of para-amino hippuric acid (PAH)

30
Q

what properties of PAH make it able to measure RPF (3)

A

freely filtered / completely secreted into tubules and not reabsorbed / completely cleared from the plasma

31
Q

what is the rate of clearance of PAH and therefore renal plasma flow

A

650ml/min

32
Q

what 3 things must clearance markers be to be effective

A

non-toxic / inert (not metabolised) / easy to measure

33
Q

what is the filtration fraction

A

fraction of plasma flowing through the glomerulus that is filtered into the tubules

34
Q

what is the filtration fraction in terms of GFR and RBF

A

GFR / RPF = 125/650 = 0.19 = 20%

My2 renal (27 decks)

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