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RENAL PHYSIOLOGY > Glomerular Filtration > Flashcards

Glomerular Filtration Flashcards

1
Q

What are the basic renal processes?

A

Filtration
Reabsorption
Secretion

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2
Q

What is the total GFR per day?

A

180L/day

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3
Q

What is the purpose of renal reabsorption?

A

Bringing substances the body wants back into the body

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4
Q

What volume of blood do the kidneys receive?

A

1200mls/min

20-25% of total cardiac output

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5
Q

Total blood volume passes through the renal circulation in:

A

<5 mins

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6
Q

What proportion of blood volume is plasma?

A

55%

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7
Q

What is a normal GFR?

A

125mls/min

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8
Q

What percentage of the renal plasma becomes glomerular filtrate?

A

19%

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9
Q

Glomerular filtration is dependent on what?

A

Balance between:
Hydrostatic forces favouring filtration
Oncotic pressure forces favouring reabsorption

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10
Q

Which factors determine the filterability of a given solute?

A

Molecular size
Electrical charge
Shape

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11
Q

What proportion of Hemoglobin is filtered out?

A

3%

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12
Q

What proportion of serum albumin is filtered out?

A

<1%

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13
Q

Pores of glomerular endothelial cells prevent what?

A

Filtration of blood cells

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14
Q

What structure prevents filtration of larger proteins?

A

Basal lamina of the glomerulus

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15
Q

What structure prevents filtration of medium sized proteins?

A

Slit membrane between pedicels

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16
Q

Why is glomerular capillary pressure higher than most capillaries in the body?

A

The Afferent arterioles are short and wide - offering little resistance

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17
Q

Why is post-capillary resistance high?

A

Efferent arterioles are long and narrow

18
Q

High resistance increases hydrostatic pressure where?

A

Upstream

19
Q

High resistance decreases pressure where?

A

Downstream

20
Q

Hydrostatic P always > oncotic pressure where?

A

Glomerular capillaries

21
Q

Why is oncotic pressure increased downstream?

A

Removal of fluid causes a relative increase in concentration of substrates

22
Q

What is the gross structure of the efferent arteriole?

A

Long and narrow

23
Q

What is the gross structure of afferent arterioles?

A

Short and wide

24
Q

What is the gromerular net filtration pressure?

A

10mmHg

25
Q

What is the colloid osmotic pressure gradient?

A

Osmotic pressure gradient into blood due to presence of proteins in the plasma but not the bowmans capsule
15mmHg

26
Q

What factors affect GFR?

A

Afferent/efferent arteriolar diameter

27
Q

What are the extrinsic controls of GFR?

A

Sympathetic VC nerves
Circulating catecholamines
Angiotensin II

28
Q

What is the effect of sympathetic VC nerves on GFR?

A

Afferent and efferent constriction

afferent more sensitive

29
Q

What is the effect of circulating catecholamines on GFR?

A

Constriction of the afferent arterioles

30
Q

What is the effect of angiotensin II on GFR?

A

Low [Angiotensin II]
Constriction of Efferent
High [Angiotensin II]
Constriction of afferent and efferent

31
Q

What is the effect of efferent arteriolar constriction on GFR?

A

Increased GFR due to increased pressure

32
Q

What is the effect of afferent arteriolar constriction on GFR?

A

Reduced GFR due to reduced pressure

33
Q

What is the effect of afferent arteriolar dilation on GFR?

A

Increased GFR due to increased pressure

34
Q

GFR autoregulation is effective over what range of BPs?

A

60-130mmHg

35
Q

Filtration falls below what MBP?

A

60mmHg

36
Q

Filtration stops below what MBP?

A

50mmHg

37
Q

If mean arterial pressure increases, what is the effect on the afferent arteriole? Why?

A

Increased afferent arteriole constriction to prevent a rise in glomerular filtration

38
Q

What is the role of sympathetic VC nerves in massive haemorrhage?

A

Override autoregulation to liberate blood for more immediately important organs

39
Q

How much blood can be ‘freed up’ to perfuse other organs at expense of the kidneys?

A

800mls

40
Q

What percentage of fluid is reabsorbed from the nephron?

A

> 19% (of 20% volume filtered)

41
Q

Which capillaries are responsible for reabsorption?

A

Peritubular capillaries

42
Q

Why are the peritubular capillaries in favour of reabsorption?

A

Higher concentrations of plasma proteins in peritubular capillaries hugely increases osmotic pressure

RENAL PHYSIOLOGY (10 decks)

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