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Systems: Urinary AB > 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 renal filtration?

A

The formation at the glomerular capillaries of an essentially protein-free filtrate of plasma, (~20%)

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3
Q

What does the high (180l/day) GFR means?

A

The kidney has ample opportunity to precisely regulate ECF volume and composition and eliminate “nasty” substances.

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4
Q

What types of substances are reabsorbed?

A

Substances that the body wants are reabsorbed, those it doesn’t want stay in the tubule and are excreted

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5
Q

In what way may substances be specifically removed from the body?

A

Secretion

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6
Q

What is the blood flow to the kidneys?

A

Kidneys receive a blood flow of  1200mls/min, ie 20-25% of total cardiac output

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7
Q

How do the kidneys have such as high BF/g of tissue?

A

They weigh less than 1% of the total body weight but receive almost a quarter of the blood flow

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8
Q

Why are the kidneys vulnerable to damage by vascular disease?

A

They have such a high BF

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9
Q

How long does it take a volume of blood equal to that of total blood volume to pass through the renal circulation?

A

<5 minutes

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10
Q

What happens to the blood that enters the Bowman’s capsule?

A
  • None of the red cells and only a fraction of the plasma is filtered through into Bowman’s capsule.
  • The remainder passes via the efferent arterioles into the peritubular capillaries and then to the renal vein.
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11
Q

What is the renal plasma flow?

A

660mls/min

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12
Q

What is the normal GFR?

A

125mils/min

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13
Q

How much of the renal plasma becomes glomerular filtrate?

A

19%

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14
Q

What is glomerular filtration dependent on?

A

The balance between the hydrostatic forces favouring filtration and the oncotic pressure forces favouring reabsorption. (Starling’s forces).

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15
Q

What determines the filterability of solutes across the glomerular filtration barrier?

A
  • Molecular size
  • Electrical charge
  • Shape
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16
Q

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

A

Because the afferent arteriole is short and wide and offer little resistance to flow. So the blood arriving at the glomerulus still has a high hydrostatic pressure.

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17
Q

What offers high post capillary resistance?

A

The unique arrangement of the efferent arteriole which is long and narrow

18
Q

What is the golden rule of circulation?

A

If you have a high resistance, hydrostatic pressure upstream is increased, while the pressure downstream is decreased.

19
Q

What is the only process which occurs at the glomerular capillaries?

A

Filtration

20
Q

Why is filtration the only process which occurs at the glomerular capillaries?

A

The hydrostatic pressure which favours filtration always exceeds the oncotic pressure

21
Q

What is the glomerular capillary pressure dependent on?

A

The afferent and efferent arteriolar diameter and therefore the balance of resistance between them

22
Q

What is the diameter of the afferent and efferent arterioles subject to extrinsic control via?

A
  • Sympathetic VC nerves leading to afferent and efferent constriction, greater sensitivity of afferent arteriole
  • Circulating catecholamines causing constriction primarily of the afferent
  • Angiotensin II causing constriction of efferent at [low], both afferent and efferent at [high]
23
Q

What is crucial in determining GFR?

A

Relative diameter of afferent and efferent arterioles

24
Q

What is autoregulation?

A

The ability of the renal vasculature to exhibit an intrinsic ability to adjust its resistance in response to changes in arterial BP to keep BP and GFR constant

25
Q

When is autoregulation effective in man?

A

Over a range of MBP from 60-130mmHg

26
Q

What happens to autoregulation below 60mmHg?

A

Filtration falls

27
Q

What happens to autoregulation at 50mmHg?

A

It ceases altogether

28
Q

What is autoregulation independent of?

A

Nerves or hormones is occurs in denervated and in isolated perfused kidneys

29
Q

How does autoregulation prevent a rise in glomerular glomerular capillary pressure?

A

If mean arterial pressure increases, there is an automatic increases in afferent arteriolar constriction to prevent a rise in glomerular capillary pressure

30
Q

What happens to the glomerular capillary pressure if the mean arterial pressure decreases?

A

Afferent arterioles dilate to decrease glomerular capillary pressure

31
Q

How can autoregulation be overridden in situations where blood volume/BP face serious compromise?

A

Activation of sympathetic VC nerves, can override autoregulation liberating blood for more immediately important organs.

32
Q

What can prolonged reduction in renal BF lead to?

A

Irreparable damage which may then lead to death because of disruption of the kidney’s role in homeostasis.

33
Q

What adaptation do athletes competing in marathons undergo?

A

Endurance training for very long events involves adaptation of skeletal muscle so that its requirement for blood flow becomes more efficient and therefore there is less need to take it from the kidneys.

34
Q

What are responsible for reabsorption?

A

Peritubular capillaries

35
Q

Why must enormous amounts of fluid be reabsorbed back into the peritubular capillaries?

A

Since 180 l/day are filtered through the glomerulus into the renal tubule, but only 1-2 l/day are excreted as urine

36
Q

What has important effects on Starling’s forces in the peritubular capillaries?

A

The unique efferent arteriole

37
Q

What important effect does the efferent arteriole have in the Starling forces in the peritubular capillaries?

A

It offers resistance along its entire length which means there is a large pressure drop meaning the hydrostatic pressure is very low ~Ppc 15mmHg

38
Q

Why does only filtration occur at the glomerular capillaries?

A

Glomerular capillary pressure> pulse pressure

39
Q

Why is the pertibular capillary pressure very low?

A

Due to the hydrostatic pressure overcoming frictional resistance in efferent arterioles

40
Q

Why do the peritubular capillaries have a higher osmotic pressure?

A

Since  20% of the plasma has filtered into Bowman’s capsule in the glomerulus, (filtration fraction), the blood remaining in the efferent arteriole and then the peritubular capillaries has a higher concentration of plasma proteins

41
Q

Why is the Starling’s forces in the peritubular capillaries in favour of reabsorption ?

A

The net result of the low peritubular capillary pressure and the high osmotic pressure is that the balance of Starling’s forces in the peritubular capillaries is entirely in favour of reabsorption

42
Q

Where is 99%H2O, 1005 of glucose, 99.5% of Na and 50% of urea filtered at the glomerulus reabsorbed?

A

Within the tubule, mainly at the proximal convoluted tubule

Systems: Urinary AB (26 decks)

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