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2 RENAL > Physiology 3 > Flashcards

Physiology 3 Flashcards

1
Q

what is glomerular filtration

A

the process where 20% of the plasma is filtered through the glomerulus into the tubular fluid

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2
Q

what are the 3 filtration barriers at the glomerulus

A

glomerular capillary endothelium

basement membrane

podocytes (glomerular epithelium)

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3
Q

how does the glomerular capillary endothelium filter the blood

A

it its as a barrier to RBCs

gaps/pores in the wall are much bigger than the pores found in other capillaries so allow smaller substances to leak through

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4
Q

what is the basement membrane made out of

A

collagen and glycoproteins

it is an acellular layer

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5
Q

what are filtration slits

A

the gaps formed by the extensions of the podocyte slit processes

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6
Q

what happens to substances small enough to fit through the 3 physical barriers in the glomerulus

A

they bass into the lumen of the renal tubule

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7
Q

what charge is the lumen of the bowman’s capsule (renal tubule)

A

negative - therefore repels positive plasma proteins making sure they stay in the capillary

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8
Q

what drives fluid filtration into the bowman’s capsule

A

4 forces that act across the glomerular membrane

  1. glomerular capillary BP
  2. Capillary oncotic pressure
  3. Bowman’s capsule hydrostatic pressure
  4. Bowman’s capsule oncotic pressure
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9
Q

how does glomerular capillary BP affect filtration

A

biggest force

increased pressure in the capillary increases filtration

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10
Q

how is glomerular capillary BP maintained

A

by the afferent capillary being wider than the efferent capillary

this means blood constants sits in the capillary keeping a constant pressure

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11
Q

how does capillary oncotic pressure affect filtration

A

there are lots of plasma proteins in the capillary but not the bowman’s capsule lumen

this then drags fluid back into the capillary from the bowman’s capsule - against net filtration

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12
Q

how does the bowman’s capsule hydrostatic pressure affect filtration

A

pressure in the bowman’s capsule push’s things out

increased pressure in the bowman’s capsule = decrease filtration

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13
Q

how does bowman’s capsule oncotic pressure have an effects on filtration

A

usually doesn’t because there are no plasma proteins in the initial tubular fluid

(affects further down in the tubule)

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14
Q

how do you work out net filtration

A

take away the forces favouring filtration from those opposing it

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15
Q

what forces favour filtration

A

capillary BP

bowman’s capsule oncotic pressure

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16
Q

what forces are against filtration

A

bowman’s capsule hydrostatic fluid pressure

capillary oncotic pressure

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17
Q

what is GFR

A

the rate at which protein free plasma is filtered from glomeruli into the bowman’s capsule

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18
Q

how do you calculate GFR

A

filtration coefficient x net filtration pressure

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19
Q

what is the biggest determinant factor of GFR

A

glomerular capillary fluid (blood) pressure

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20
Q

what extrinsic regulation is used to control renal blood flow

A

sympathetic control via baroreceptor reflex

21
Q

what auto regulation of renal blood flow and GFR is there

A

myogenic mechanism

tubuloglomerular feedback mechanism

22
Q

how can you change the BP in the glomerular capillary

A

by changing the diameter of the afferent arteriole

23
Q

how does the baroreceptor reflex extrinsically control GFR/ glomerular capillary bp

A

fall in BP leads to decreased arterial bp -

detected by aortic and carotid sinus baroreceptors -

increases sympathetic activity

causes generalised arteriolar vasoconstriction -

construction of afferent arterioles -

decreased BP in glomerular capillary -

decreased GFR -

decreased urine volume

(this helps compensate for fall in blood volume)

24
Q

why is there the need for intrinsic control as well as extrinsic control of GFR

A

so that GFR doesn’t decrease every time there is a transient fall/ rise in blood pressure

still need to produce enough urine to get rid of metabolic waste products

25
Q

how does myogenic intrinsic regulation of GFR work

A

when vascular smooth muscle is stretched (eg. with a BP increase) stretch receptors cause it to contract in response

this keeps GFR constant when BP rises suddenly and transiently

26
Q

how does tubuloglomerular feedback work in the intrinsic regulation fo GFR

A

iIf GFR rises there is an increase of NaCl going through the tubule

this is sensed by MACULA DENSA cells in the juxtaglomerular apparatus causing chemicals to be released which constricts the afferent arterioles

this negative feedback brings back GFR to norm if there is too much NaCl loss

27
Q

what are some other determinants of GFR

A
  1. normal net filtration pressure
  2. increase in bowman’s capsule pressure (increases with blockage in urinary system)
  3. increase in capillary oncotic pressure (dehydration)
  4. decrease in capillary oncotic pressure (burns)
  5. change in surface area available for filtration (how permeable the membrane is)
28
Q

what is plasma clearance

A

the volume of plasma completely cleared of a substance per minute

(every substance has a specific plasma clearance value)

29
Q

how do you calculate the plasma clearance of a substance

A

concentration of substance in urine x volume of urine / concentration of substance in plasma

30
Q

what substance has a plasma clearance than is = to GFR

A

Inulin

31
Q

why is inulin not used routinely to check GFR

A

because it needs to be infused into the patient until there is a constant plasma concentration therefore is not practical

32
Q

what is creatinine

A

substance produced by muscles at a constant rate

freely filtered with no tubular reabsorption and little tubular secretion so a good marker of GFR

33
Q

what percentage of glucose filtered through the glomerulus is reabsorbed in the tubules

A

100% therefore plasma clearance = 0 as excretion = 0

should be no glucose in the urine

34
Q

what % of urea is absorbed and what % is excreted

A

50% absorbed

50% excreted

35
Q

why is hydrogen plasma clearance > GFR

A

because hydrogen ions are freely filtered and then more are secreted into the tubules from the capillaries

H+ ions are not reabsorbed back into blood

36
Q

what 2 substances have a plasma clearance that can be taken as GFR

A

Inulin

creatinin

37
Q

what is normal GFR

A

125 ml/min

38
Q

what is renal plasma flow

A

collectively how much plasma is flowing through both kidneys at a time

39
Q

how do you measure renal plasma flow

A

para-amino hippuric acid

filtered freely in glomerulus, secreted and not absorbed, completely cleared from plasma

40
Q

what 2 things do renal plasma flow markers need to do

A

get freely filtered and completely secreted

41
Q

what is the filtration fraction

A

percentage of plasma that enters the glomeruli which is then filtered

42
Q

how do you calculate the filtration fraction

A

GFR/Renal plasma flow

43
Q

what is a normal renal plasma flow

A

650 ml/min

44
Q

what is renal plasma flow

A

collectively how much plasma is flowing through both kidneys at a time

45
Q

how do you measure renal plasma flow

A

para-amino hippuric acid

filtered freely in glomerulus, secreted and not absorbed, completely cleared from plasma

46
Q

what 2 things do renal plasma flow markers need to do

A

get freely filtered and completely secreted

47
Q

what is the filtration fraction

A

percentage of plasma that enters the glomeruli which is then filtered

48
Q

how do you calculate the filtration fraction

A

GFR/Renal plasma flow

49
Q

what is a normal renal plasma flow

A

650 ml/min

2 RENAL (20 decks)

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