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HUBS192 > 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?

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
What is the formula for the renal clearance of a substance?
Cs=(UsxV)/P
26
What are the units of renal clearance?
ml/min
27
What is Us?
Concentration of S in the urine (mg/L or mol/L)
28
What is V?
Volume of urine produced per unit time (mL/min or L/hour)
29
What is Ps?
Concentration of S in plasma (mg/L or mol/L)
30
What does the renal clearance equation describe?
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
What is glomerular filtration rate (GFR)?
Amount of fluid filtered per unit time
32
What is GFR normally?
180L/day or 125 ml/minute
33
Is GFR tightly regulated?
Yes
34
Does GFR vary?
Yes from person to person
35
When does GFR decline?
Slowly from the age of 30 as nephrons die
36
What must a substance be to be used as a measure of GFR?
Not reabsorbed from the tubule, not be secreted into the tubule and not metabolised (only filtered)
37
What are the two main substances used to measure GFR?
Inulin and creatinine
38
What is inulin?
A polysaccharide not metabolised by the body
39
Where is inulin found?
Not in the body so must be injected
40
What is creatinine?
A waste product produced by muscles
41
Where is creatinine?
Already in the body so most commonly used clinically
42
What is an indicator for kidney function?
Plasma creatinine
43
How is plasma creatinine if both kidneys are working (GFR=125ml/min)?
Low
44
How is plasma creatinine if only one kidney is working (GFR= 60ml/min)?
Fairly normal
45
What is critical kidney function?
GFR=25ml/min (some drugs can be given if it gets past this point)
46
What is renal blood flow (RBF)?
25% CO/min = 1.25L blood/min
47
What is blood made up of?
About half plasma and half cells
48
What is renal plasma flow (RPF)?
625mL plasma/min
49
How much of RPF is filtered?
125mL (20%)
50
What is the filtration fraction?
GFR/RPF
51
What is filtered load?
Amount of a particular substance (Solute) filtered per minute
52
What is the formula for filtered load?
GFR x Solute plasma concentration

HUBS192 (38 decks)

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