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HUBS192 2024 > Lecture 32: GLOMERULAR FUNCTION > Flashcards

Lecture 32: GLOMERULAR FUNCTION Flashcards

1
Q

What is filtration?

A

A specific form of ultrafiltration

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2
Q

What does filtration create?

A

A plasma-like filtrate of the blood

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3
Q

How is filtration at the glomerulus?

A

Not particularly selective

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4
Q

What is the rate of filtration?

A

125ml/min (180L/day)

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5
Q

How much urine is produced from filtration?

A

Only 1.5 L/day

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6
Q

What does the glomerulus have?

A

Afferent and efferent arterioles (entering/leaving) supplying the glomerulus with blood for filtration

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7
Q

What portion of cardiac output goes to kidneys?

A

20-25%

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8
Q

What portion of cardiac output goes to the brain?

A

13%

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9
Q

What portion of cardiac output goes to the heart?

A

4%

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10
Q

How many litres of blood per minute go to the kidneys?

A

1-1.2 (~400mL/100g/min)

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11
Q

What amount of blood goes to the brain?

A

~50ml/100g/min

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12
Q

What amount of blood goes to the heart?

A

~80ml/100g/min

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13
Q

What is the high blood flow to the kidneys for?

A

Filtration not metabolism

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14
Q

What happens with small substances with low molecular mass at the filtration barrier?

A

They are freely filtered

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15
Q

What happens with large substances with high molecular mass at the filtration barrier?

A

They are not filtered

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16
Q

What are driving forces determined by?

A
  • forces/pressure gradients between glomerular capillary (blood side) and capsular space (urine side)
  • permeability of glomerular capillary
  • surface area of glomerular capillary
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17
Q

What is net filtration pressure?

A

10mmHg

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18
Q

What are the four forces determining net filtration pressure?

A

Glomerular hydrostatic pressure (GHS), blood colloid osmotic pressure (BCOP), capsular hydrostatic pressure (CsHP) and capsular colloid osmotic pressure (CsCOP)

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19
Q

What are the forces favouring filtration?

A

Glomerular hydrostatic pressure (GHP) and capsular colloid osmotic pressure (CsCOP)

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20
Q

What are the forces opposing filtration?

A

Blood colloid osmotic pressure (BCOP) and capsular hydrostatic pressure (CHP)

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21
Q

What is glomerular hydrostatic pressure?

A

Blood pressure

22
Q

What is blood colloid osmotic pressure?

A

Albumin

23
Q

What is capsular hydrostatic pressure?

A

Corpuscle embedded in tissue so can’t expand much

24
Q

What is capsular colloid osmotic pressure?

A

No proteins in the capsular space so is 0

25
Q

What is the formula for the renal clearance of a substance?

A

Cs=(UsxV)/P

26
Q

What are the units of renal clearance?

A

ml/min

27
Q

What is Us?

A

Concentration of S in the urine (mg/L or mol/L)

28
Q

What is V?

A

Volume of urine produced per unit time (mL/min or L/hour)

29
Q

What is Ps?

A

Concentration of S in plasma (mg/L or mol/L)

30
Q

What does the renal clearance equation describe?

A

The rate at which a substance is cleared by the kidneys per unit time for all substances which can be detected in the plasm and urine

31
Q

What is glomerular filtration rate (GFR)?

A

Amount of fluid filtered per unit time

32
Q

What is GFR normally?

A

180L/day or 125 ml/minute

33
Q

Is GFR tightly regulated?

A

Yes

34
Q

Does GFR vary?

A

Yes from person to person

35
Q

When does GFR decline?

A

Slowly from the age of 30 as nephrons die

36
Q

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

A

Not reabsorbed from the tubule, not be secreted into the tubule and not metabolised (only filtered)

37
Q

What are the two main substances used to measure GFR?

A

Inulin and creatinine

38
Q

What is inulin?

A

A polysaccharide not metabolised by the body

39
Q

Where is inulin found?

A

Not in the body so must be injected

40
Q

What is creatinine?

A

A waste product produced by muscles

41
Q

Where is creatinine?

A

Already in the body so most commonly used clinically

42
Q

What is an indicator for kidney function?

A

Plasma creatinine

43
Q

How is plasma creatinine if both kidneys are working (GFR=125ml/min)?

A

Low

44
Q

How is plasma creatinine if only one kidney is working (GFR= 60ml/min)?

A

Fairly normal

45
Q

What is critical kidney function?

A

GFR=25ml/min (some drugs can be given if it gets past this point)

46
Q

What is renal blood flow (RBF)?

A

25% CO/min = 1.25L blood/min

47
Q

What is blood made up of?

A

About half plasma and half cells

48
Q

What is renal plasma flow (RPF)?

A

625mL plasma/min

49
Q

How much of RPF is filtered?

A

125mL (20%)

50
Q

What is the filtration fraction?

A

GFR/RPF

51
Q

What is filtered load?

A

Amount of a particular substance (Solute) filtered per minute

52
Q

What is the formula for filtered load?

A

GFR x Solute plasma concentration

HUBS192 2024 (38 decks)

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