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HUBS192 > Lecture 32 Physio Glomerular function > Flashcards

Lecture 32 Physio Glomerular function Flashcards

1
Q

whats filtration (nephron process)?

A

specific form of ultrafiltration

– creates a plasma-like filtrate of the blood

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2
Q

where does filtration occur?

A

at the glomeruli is not particularly selective

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3
Q

whats the filtration rate and volume of urine?

A

rate of 125mL/min (180L/day)

– produces only 1.5L of urine/day

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4
Q

What defines renal filtration?

A
  • renal blood flow
  • filtration barrier
  • driving forces
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5
Q

what supplies the glomerulus with blood for filtration?

A

glomerulus has afferent and efferent arterioles (entering/leaving)

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6
Q

what is the renal blood supply?

A

• 20-25% of cardiac output (CO)
(brain 13%, heart 4 %)

• 1-1.2L/min (~ 400mL/100g/min)
(brain ~50mL/100g/min, heart ~80mL/100g/min)

• high flow for filtration rather than metabolism

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7
Q

what is the filtration membrane composed of?

A

fenestrated endothelium, basement membrane and

podocytes with foot processes and filtration slits

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8
Q

whats freely filtered?

A

small substances (low molecular mass)

eg K+, Na+, Cl-, H2O, Urea, Glucose

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9
Q

whats NOT filtered?

A

large substances (high molecular mass)

eg hemoglobin, serum albumin

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10
Q

what is glomerular filtration determined by?

A
  • forces / pressure gradients between glomerular capillary / Bowman’s space
  • permeability of glomerular capillary
  • SA of glomerular capillary
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11
Q

what are the 4 forces (pressures) determining net glomerular filtration pressure (10 mmHg)?

A
  • glomerular hydrostatic (GHP)
  • blood colloid osmotic pressure (BCOP)
  • capsular hydrostatic pressure (CsHP)
  • capsular colloid osmotic pressure (CCOP)
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12
Q

whats glomerular hydrostatic (GHP)?

A

blood pressure (+ 50 mmHg)

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13
Q

whats blood colloid osmotic pressure (BCOP)?

A

albumin (- 25 mmHg)

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14
Q

whats capsular hydrostatic pressure (CsHP)?

A

corpuscule embedded in tissue (- 15 mmHg)

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15
Q

whats capsular colloid osmotic pressure (CCOP)?

A

no protein in capsular space (+ 0 mmHg)

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16
Q

Filtration in the kidney
A. is dependent on the osmotic force in the Bowman’s space.
B. results in high protein load of the primary urine.
C. results in an isotonic primary filtrate.
D. results in an absence of glucose in the primary urine.
E. is independent of serum albumin.

A

C. results in an isotonic primary filtrate.

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17
Q

How can we define renal filtration?

A

Renal Clearance

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18
Q

whats Renal Clearance equation?

A

Clearance (Cs) = Us x V / Ps (in mL/min)

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19
Q

Clearance (Cs) = Us x V / Ps (in mL/min)

A 
Cs = Clearance of substance
Us = concentration of S in urine (mg/L or mol/L)
V = volume of urine produced (mL/min or L/hour)
Ps= concentration of S in plasma (mg/L or mol/L)
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20
Q

what does the equation describe?

Clearance (Cs) = Us x V / Ps (in mL/min)

A

rate at which substance S is cleared by the kidneys per unit time.

clearance via the kidneys for all substances that can be detected in plasma and urine!!!

21
Q

whats glomerular filtration rate (GFR)?

A

• amount of fluid filtered per unit time

  • tightly regulated
  • variation from person to person
  • declines slowly from age 30
22
Q

whats glomerular filtration rate (GFR) normally?

A

~180 L/day or 125 mL/minute

23
Q

what must a substance be to be used as a measure of GFR?

A
  • not be reabsorbed from the tubule
  • not be secreted into the tubule
  • not be metabolised
24
Q

what are the two main substances that can be used as a measure of GFR?

A

inulin

creatinine

25
Q

whats inulin?

A
  • polysaccharide not metabolised by body

* not found in body, must be injected

26
Q

whats creatinine?

A
  • waste product produced by muscles

* already in the body so most commonly used clinically

27
Q

is creatine filtered freely?

A

yes at the glomerulus

28
Q

what cant creatinine do?

A

be reabsorbed, secreted or metabolised

29
Q

whats the ideal measurement for clinically estimating GFR?

A

measuring the renal clearance of creatinine

30
Q

what is plasma creatinine?

A

mg/dL

indicator for kidney function

31
Q

what happens if plasma creatinine is low?

A

both kidneys are working (125mL/min)

32
Q

what happens if only one kidney is working (60mL/min)

A

plasma creatinine is normal

33
Q

How much of the blood reaching the kidney is filtered?

A

Filtration fraction

34
Q

whats RBF?

A

Renal Blood Flow
= 25 % C.O. /min = 1.25L blood/min
blood is about half plasma / half cells

35
Q

whats RPF?

A

Renal plasma flow
625 ml plasma/min
but only 125 ml/min filtered (GFR)

36
Q

where does rest flow through?

A

into efferent arteriole

37
Q

whats the Filtration Fraction?

A

GFR/RPF

38
Q

whats the filtration fraction?

(RBF) = 1.25L blood /min
(RPF) = 625 ml plasma/min
(GFR) = 125 ml/min filtered
A

only 20 % (125/625) of plasma is filtered

39
Q

whats filtered load?

A

amount of a particular substance (solute) filtered per minute

40
Q

whats the equation for filtered load?

A

GFR x solute plasma conc.

41
Q

whats the filtered load?
GFR 125 ml/min = 0.125 L/min
plasma glucose = 5 mmol/L

A

filtered load = 0.125 L/min x 5 mmol/L

= 0.625 mmol/min

42
Q

The glomerular filtration rate (GFR) is defined
A. as the amount of substance filtered per time.
B. as the volume of urine produced per day.
C. as the amount of water both kidneys reabsorb per day.
D. as the volume of plasma filtered per time.
E. the amount of sodium filtered per time.

A

D. as the volume of plasma filtered per time.

43
Q

summary

whats renal filtration?

A

renal blood flow, the

filtration barrier and the driving forces;

44
Q

summary

what can renal clearance of a substance be determined by?

A

CS = US x V/PS (in mL/min)

45
Q

what can GFR be estimated by?

A

clearance of creatinine as creatinine is only filtered

46
Q

what does the filtration fraction define?

A

ratio between perfusion and filtration in the kidney (GFR/RPF);

47
Q

whats filtered load units?

A

g/min or mol/min

48
Q

whats filtered load?

A

amount of a substance filtered per time (GFR x PS)

HUBS192 (36 decks)

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