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Renal Physiology > Filtration and Clearance > Flashcards

Filtration and Clearance Flashcards

1
Q

where does plasma filter in the kidney? what type of ultrafiltrate is produced?

A

filters in the glomerular capillaries into Bowman’s space

forms protein free ultrafiltrate with plasma ion levels

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2
Q

what causes the net efflux of ultrafiltrate?

A

differences in the oncotic and hydrostatic pressure across the glomerular capillaries

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3
Q

what is the normal GFR? how long does it take to filter out the ECF volume?

A

125 ml/min or 180L per day

2 hours

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4
Q

what is the filtration coefficient of the glomerular capillary?

A

Kf

the product of capillary hydraulic conductivity and the surface area of filtration

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5
Q

how does capillary hydrostatic pressure change from beginning to end of the glomerular capillary? what is this due to?

A

only by 3 mmHg (small proportion of the total)

this is due to post capillary efferent arteriole constriction

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6
Q

how does the oncotic pressure of the glomerular capillary change from beginning to end? how about the oncotic pressure of the bowman’s capsule?

A

glomerular capillary- from 25 mmHg to 35mmHg

bowman’s capsule- always 0 mmHg

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7
Q

what is the hydrostatic pressure in the bowman’s capsule?

A

10 mmHg

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8
Q

why does so much more plasma filter into the bowman’s capsule compared to other body tissues?

A

because the filtration coefficient is so large and the capillary hydrostatic pressure does not change much due to arteriole constriction

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9
Q

where does glomerular filtration cease?

A

where starling forces cancel each other out towrad the efferent end of the capillary

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10
Q

describe the basment membrane of the glomerular capillaries and how it effects filtration`

A

their basement membrane restrict filtration of solutes >1 KDa and its anionic charge favors cation and restricts anion filtration

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11
Q

what cells have foot processes covering glomerular capillaries? what are their purpose?

A

podocytes

their anionic charge further restricts anionic protein filtration

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12
Q

what do the fenestrations of the glomerular capillaries filter out?

A

prevent cellular components from being filtered towards the basement membrane

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13
Q

which molecules are freely filtered through the bowman’s capsule?

A

water and solutes with a diameter of <4nm

the greater the size, the less likely it is to get filtered out

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14
Q

out of the plasma proteins myoglobin, hemoglobin, albumin and insulin, which ones are most likely to be seen in the ultrafiltrate?

A

insulin (freely filtered) > myoglobin > hemoglobin > albumin

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15
Q

what would occur if charge was removed from the glomerular barrier? what disease is this associated with?

A

it would increase the passage of anions and overall proteins into the ultrafiltrate
associated with nephritis

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16
Q

what is the cardiac output at rest equivalent to? how much of this perfuses the kidney?

A

equivalent to blood volume

20% of CO perfuses kidney

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17
Q

how do renal blood flow and renal plasma flow relate? how much of this plasma is filtered at the glomeruli?

A

RPF is 55% of RBF

GFR is 20% of RPF

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18
Q

what is the filtration fraction?

A

FF=GFR/RPF (fraction of plasma that is filtered out of the blood and into the bowman’s capsule)
about .2 in a normal person

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19
Q

how many liters of plasma does the kidney filter per day? how does this compare to the ECF volume?

A

180L which is 10 times the total ECF volume

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20
Q

how does GFR and the rate of urine excretion change with fluid consumed?

A

GFR stays the same but the amount of urine excreted varies

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21
Q

what occurs to GFR and FF with increasing RPF? how does this occur?

A

GFR increrases and FF decreases
a greater surface area of the glomerular capillaries filter plasma until maximal rate is achieved
this is still a smaller fraction due to the increased flow

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22
Q

describe the relationship between FF and RPF. why does this occur?

A

greater fraction of the RPF is filtered at lower rates and a smaller fraction is filtered at high RPF
maintains GFR at levels necessary for renal function when RPF is compromised

23
Q

what does afferent arteriolar constriction doe to glomerular capillary hydrostatic pressure, RPF and GFR?

A

decreases capillary hydrostatic pressure
RPF decreases
GFR decreases

24
Q

what does efferent arteriolar constriction doe to glomerular capillary hydrostatic pressure, RPF and GFR?

A

increases capillary hydrostatic pressure
RPF decreases
GFR increases

25
Q

what does efferent and afferent arteriolar constriction doe to glomerular capillary hydrostatic pressure, RPF and GFR?

A

no change on capillary hydrostatic pressure
RPF decreases
GFR stays the same

26
Q

what effects does increasing or decreasing plasma protein levels have on GFR?

A

increasing- decreases GFR

decreasing- increases GFR

27
Q

what effect does ureter obstruction have on RPF and GFR?

A

no change on RPF

decreases GFR by increasing glomerular hydrostatic pressure

28
Q

what causes fluid reabsorption in the post glomerular peritubular capillaries?

A

starling forces

the peritubular capillary oncotic pressure difference exceeds hydrostatic pressure difference that opposes absorption

29
Q

describe the relationship of the glomerular and peritubular capillaries

A

the peritubular capillary is a continuation of the glomerular efferent capillary

30
Q

describe the net absorptive pressure along the peritubular capillaries?

A

it decreases from 17mmHg to 12 mmHg

absorption is greater at the beginning of the peritubular capillary

31
Q

what measurement provides an index of the number of functioning nephrons in kidney disease? when does renal failure begin?

A

GFR measurement

renal failuer when GFR decreases to below 20 ml/min or a loss of function of 85% of nephrons

32
Q

what is renal clearance?

A

the virtual volume of plasma from which a solute is completely removed from by the kidney per unit of time (rate of ml/min)

33
Q

under what conditions can renal clearance of a solute be used to measure GFR?

A

if the solute is freely filtered at the glomerulus, if it is not reabsorbed or secreted in the nephron, and if it is not synthesized or metabolized in the kidney

34
Q

what is inferred about GFR by the renal clearance of an appropriate solute? (equation included)

A

plasma solute concentration x GFR = urine solute concentration x rate of urine flow
can use this equation to measure GFR

35
Q

how does the amount of solute filtered in a given time compare to the amount of solute excreted at a given time? what is this fact used for?

A

they are equal

provides the derivation for finding the GFR

36
Q

what exogenous solute is used to measure GFR? how is this done?

A

inulin- a fructose polymer (measured very accurately)

given by IV infusion to maintain constant plasma levels and measured in plasma and urine

37
Q

what endogenous solute is used to measure GFR? how is this done?

A

creatinine in the absence of strenuous exercise and disease a constant rate of creatinine diffuses from skeletal muscle to plasma

38
Q

what does increased plasma creatinine indicate?

A

decreased clearance from the plasma (major way to detect GFR)
decreased GFR resulting from decreased number of functioning nephrons

39
Q

what is the normal amount of plasma creatinine? how does the kidney metabolism of creatinine impact GFR estimation?

A

1mg/100ml

minor secretion by the kidney results in 10% over estimation of GFR

40
Q

what is the equation for clearance of any solute? what does clearance depend on?

A

clearance= (urine concentration of the solute x rate of urine flow)/plasma concentration of solute
depends on amount that is reabsorbed in the nephron

41
Q

what are the possibilities of renal handling of a solute?

A

just resorption, just secretion or a combination of resorption and secretion in the same or different segments of a nephron

42
Q

what do clearance ratios use for comparison? what do they indicate?

A

compare clearance of a solute to inulin or creatinine.

1 indicates net solute secretion into tubular fluid

43
Q

what is the fractional excretion of water?

A

the fraction of the glomerular filtrate not reabsorbed from the nepron (excreted)

44
Q

how does fractional excretion of water compare to the GFR?

A

FE H2O= rate of urine excretion/GFR

45
Q

how does fractional excretion of water relate to inulin concentrations? can this property be transferred to creatinine?

A

FE H2O= plasma concentration of inulin/ urine concentration of inulin
this also can be used for creatinine clearance

46
Q

what is the fractional excretion of solute? how is it estimated?

A

the fraction of filtered solute which appears in urine

estimated as the ratio of solute clearance to GFR

47
Q

what are the equations for fractional excretion of solute?

A

=clearance of solute/clearance of creatine
=(urine concentration of solute x plasma concentration of creatine)/ (urine concentration of creatine x plasma concentration of solute)

48
Q

when water and Na balance, what is the fractional excretion of water and Na? what happens in dehydration and positive water balance?

A

both are 1%

dehydration: FE H2O < 1% and FE Na=1%
positive: FE H2O > 5% and FE Na= 1%

49
Q

what is fractional reabsorption?

A

fraction of filtered water or solute which is reabsorbed

1-FE

50
Q

how does the kidney modulate renal blood flow?

A

renal vascular resistance increases and decreases with increased and decreased MAP keeping blood flow fairly constant

51
Q

what is the equation for renal blood flow?

A

RBF= (renal A-V blood pressure) / renal vascular resistance

52
Q

what causes autoregulation of RBF?

A

myogenic response of renal vasculature to pressure changes

53
Q

what senses the increase or decrease in GFR? what is the result?

A

tubuloglomerular feedback at macula densa cells sense increase or decrease in GFR
cause increased or decreased resistance of afferent arteriole by contraction or relaxation

Renal Physiology (12 decks)

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