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Urinary > Glomerular Filtration > Flashcards

Glomerular Filtration Flashcards

1
Q

What is filtration?

A

Filtration is the formation of an essentially protein-free filtrate of plasma - separating a liquid component from the plasma. The formation of the liquid occurs at the glomerular capillaries

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2
Q

What is filtration?

A

Filtration is the formation of an essentially protein-free filtrate of plasma - separating a liquid component from the plasma. The formation of the liquid occurs at the glomerular capillaries

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3
Q

Why is reabsorption important?

A

Such a high volume is filtered that there are many important molecules which need to be reabsorbed for use by the body

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4
Q

What is reabsorbed from the proximal tubule?

A

NaCl (some)
Water (some)
Amino acids
Sugars

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5
Q

What is reabsorbed at the distal tubule?

A

NaCl (some)

Water (some)

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6
Q

What is the renal process secretion?

A

Specific substances that are unwanted in the body being secreted into the kidney tubules for excretion

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7
Q

What forces the kidney to filter plasma at a very high rate?

A

The high proportion of cardiac output that they receive (25%)

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8
Q

How long does it take for a volume of blood equivalent to the total body volume to pass through the renal circulation? What does this mean with regard to vulnerability?

A
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9
Q

Are RBCs filtered through the Bowman’s capsule?

A

No

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10
Q

Is the plasma filtered through Bowman’s capsule? What happens to the rest?

A

Only a small fraction, the remainder pass through afferent arterioles into the peritubular capillaries and then into the renal vein

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11
Q

What percentage of total blood volume is made up by plasma?

A

~ 55%

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12
Q

What is the normal renal plasma flow?

A

660mls/min

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13
Q

Does glomerular filtration occur in the same way as fluid entry to capillaries?

A

Yes

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14
Q

Describe the forces relating to glomerular filtration?

A

It is dictated by the balance of the hydrostatic forces favouring filtration and the oncotic pressures favouring reabsorption (Starling’s forces)

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15
Q

What is the relationship between the molecular weight and radius of a molecule and the amount that ends up in the filtrate?

A

The greater the molecular weight and size, the less of the substance will make it into the filtrate thanks to the filtering membranes

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16
Q

Describe the glomerular capillary pressure

A

The pressure of the glomerular capillary is higher than most of the bodies capillaries because the afferent (incoming) arteriole is shorter than the efferent (outgoing) and therefore the resistance coming into the glomerulus is low and high volume approaches, but the afferent vessels are long and narrow, increasing resistance and therefore increasing pressure upwards of the vessel - the glomerulus - and this ultimately provides the pressure to enable fast and efficient filtration

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17
Q

What is the ‘golden rule of circulation’?

A

If there is high resistance, there is increased hydrostatic pressure upstream of the point of resistance and decreased downstream of the point of resistance

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18
Q

Does reabsorption occur in the glomerular capillary?

A

No, only filtration, the hydrostatic pressure always favours filtration

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19
Q

What is the relationship between the osmotic pressure and the filtration pressure?

A

The filtration pressure is always higher in a healthy kidney, but the oncotic pressure counteracts this to a degree. The net filtration pressure must always be positive and its size reflects the force of filtration

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20
Q

What is the main mediator of the glomerular filtration rate? What controls this (thee things)

A

The difference in diameter between the afferent and efferent arterioles.

  1. The sympathetic VC nerves which constricts the afferent and afferent arterioles - the afferent arteriole has greater sensitivity
  2. Circulating catecholamines cause constriction primarily of the afferent arteriole
  3. Angiotensin II causing constriction of the efferent arteriole at low pressure to increase the pressure difference and constriction of the afferent arteriole at high pressure to bring the pressure balance closer together and reduce pressure in the glomerulus and thus GFR
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21
Q

Describe the change in diameter of the afferent arteriole on the GFR and pressure

A

If the afferent arteriole narrows, its diameter becomes closer to the efferent arteriole and created more of a pressure balance, reducing pressure in the glomerulus and as a result a reduced filtration rate. The reverse happens when the diameter of the afferent arteriole increases

The emphasis is on the afferent arteriole because its has a higher vasoconstrictive sensitivity, the efferent arteriole is more constant in terms of diameter

22
Q

What is significant about the renal circulation with respect to GFR?

A

It exhibits an INTRINSIC ability to adjust its resistance in response to changes in arterial BP

This keeps BF and GFR more or less constant = AUTOREGULATION

This is independent of nerves or hormones

23
Q

Over what range is the autorelgulatory mechanism of the renal vasculature effective?

A

60-130mmHg

This is why in severe blood loss the body goes into acute renal failure as the range drops below the renal ability to regulate the pressure i the glomerulus

24
Q

What is dangerous about hypovolaemia/hypovolaemic shock in relation to kidney function?

A

If the blood volume drops too low, it is impossible for the body to maintain a pressure within the range required for auto regulation, causing renal failure. This may be made much worse as the body redirects large portions of blood to other organs to try to preserve their function, further depriving the kidneys and overriding auto regulation and leading to permanent kidney damage

25
Q

Do the peritubular capillaries favour or resist reabsorption of water from the nephron? What stimulates that in relation to the plasma in the capillaries? Describe the reabsorption of some molecules into the peritubular capillaries as a result of this?

A

Reabsorption from the nephron
The plasma in the peritubular capillaries has been concentrated, decreasing the hydrostatic pressure and increasing the oncotic pressure, forcing reabsorption. This is the exact opposite of the situation in the glomerulus - the pressures are switched and this is why the glomerulus favours filtration whereas the peritubular capillaries favour reabsorption

More than 90% of water, glucose (100%) and sodium are reabsorbed as well as 50% of the urea are reabsorbed in the nephron, mainly the proximal convoluted part

26
Q

Do the peritubular capillaries favour or resist reabsorption of water from the nephron? What stimulates that in relation to the plasma in the capillaries? Describe the reabsorption of some molecules into the peritubular capillaries as a result of this?

A

Reabsorption from the nephron
The plasma in the peritubular capillaries has been concentrated, decreasing the hydrostatic pressure and increasing the oncotic pressure, forcing reabsorption. This is the exact opposite of the situation in the glomerulus - the pressures are switched and this is why the glomerulus favours filtration whereas the peritubular capillaries favour reabsorption

More than 90% of water, glucose (100%) and sodium are reabsorbed as well as 50% of the urea are reabsorbed in the tubule, mainly the proximal convoluted part

27
Q

Why is reabsorption important?

A

Such a high volume is filtered that there are many important molecules which need to be reabsorbed for use by the body

28
Q

What is reabsorbed from the proximal tubule?

A

NaCl (some)
Water (some)
Amino acids
Sugars

29
Q

What is reabsorbed at the distal tubule?

A

NaCl (some)

Water (some)

30
Q

What is the renal process secretion?

A

Specific substances that are unwanted in the body being secreted into the kidney tubules for excretion

31
Q

What forces the kidney to filter plasma at a very high rate?

A

The high proportion of cardiac output that they receive (25%)

32
Q

How long does it take for a volume of blood equivalent to the total body volume to pass through the renal circulation? What does this mean with regard to vulnerability?

A
33
Q

Are RBCs filtered through the Bowman’s capsule?

A

No

34
Q

Is the plasma filtered through Bowman’s capsule? What happens to the rest?

A

Only a small fraction, the remainder pass through afferent arterioles into the peritubular capillaries and then into the renal vein

35
Q

What percentage of total blood volume is made up by plasma?

A

~ 55%

36
Q

What is the normal renal plasma flow?

A

660mls/min

37
Q

Does glomerular filtration occur in the same way as fluid entry to capillaries?

A

Yes

38
Q

Describe the forces relating to glomerular filtration?

A

It is dictated by the balance of the hydrostatic forces favouring filtration and the oncotic pressures favouring reabsorption (Starling’s forces)

39
Q

What is the relationship between the molecular weight and radius of a molecule and the amount that ends up in the filtrate?

A

The greater the molecular weight and size, the less of the substance will make it into the filtrate thanks to the filtering membranes

40
Q

Describe the glomerular capillary pressure

A

The pressure of the glomerular capillary is higher than most of the bodies capillaries because the afferent (incoming) arteriole is shorter than the efferent (outgoing) and therefore the resistance coming into the glomerulus is low and high volume approaches, but the afferent vessels are long and narrow, increasing resistance and therefore increasing pressure upwards of the vessel - the glomerulus - and this ultimately provides the pressure to enable fast and efficient filtration

41
Q

What is the ‘golden rule of circulation’?

A

If there is high resistance, there is increased hydrostatic pressure upstream of the point of resistance and decreased downstream of the point of resistance

42
Q

Does reabsorption occur in the glomerular capillary?

A

No, only filtration, the hydrostatic pressure always favours filtration

43
Q

What is the relationship between the osmotic pressure and the filtration pressure?

A

The filtration pressure is always higher in a healthy kidney, but the oncotic pressure counteracts this to a degree. The net filtration pressure must always be positive and its size reflects the force of filtration

44
Q

What is the main mediator of the glomerular filtration rate? What controls this (thee things)

A

The difference in diameter between the afferent and efferent arterioles.

  1. The sympathetic VC nerves which constricts the afferent and afferent arterioles - the afferent arteriole has greater sensitivity
  2. Circulating catecholamines cause constriction primarily of the afferent arteriole
  3. Angiotensin II causing constriction of the efferent arteriole at low pressure to increase the pressure difference and constriction of the afferent arteriole at high pressure to bring the pressure balance closer together and reduce pressure in the glomerulus and thus GFR
45
Q

Describe the change in diameter of the afferent arteriole on the GFR and pressure

A

If the afferent arteriole narrows, its diameter becomes closer to the efferent arteriole and created more of a pressure balance, reducing pressure in the glomerulus and as a result a reduced filtration rate. The reverse happens when the diameter of the afferent arteriole increases

The emphasis is on the afferent arteriole because its has a higher vasoconstrictive sensitivity, the efferent arteriole is more constant in terms of diameter

46
Q

What is significant about the renal circulation with respect to GFR?

A

It exhibits an INTRINSIC ability to adjust its resistance in response to changes in arterial BP

This keeps BF and GFR more or less constant = AUTOREGULATION

This is independent of nerves or hormones

47
Q

Over what range is the autorelgulatory mechanism of the renal vasculature effective?

A

60-130mmHg

This is why in severe blood loss the body goes into acute renal failure as the range drops below the renal ability to regulate the pressure i the glomerulus

48
Q

What is dangerous about hypovolaemia/hypovolaemic shock in relation to kidney function?

A

If the blood volume drops too low, it is impossible for the body to maintain a pressure within the range required for auto regulation, causing renal failure. This may be made much worse as the body redirects large portions of blood to other organs to try to preserve their function, further depriving the kidneys and overriding auto regulation and leading to permanent kidney damage

49
Q

What portion of the 100% plasma volume that enters the afferent arteriole is filtered in the glomerulus? What portion is then reabsorbed in the tubules? What happens to the portion that is nor filtered in the glomerulus?

A

20%

19% - around 1% is excreted to the external environment

The remaining 80% continues through the efferent arterioles into the peritubular capillaries and into the renal vein, going back into the circulation

50
Q

Do the peritubular capillaries favour or resist reabsorption of water from the nephron? What stimulates that in relation to the plasma in the capillaries? Describe the reabsorption of some molecules into the peritubular capillaries as a result of this?

A

Reabsorption from the nephron
The plasma in the peritubular capillaries has been concentrated, decreasing the hydrostatic pressure and increasing the oncotic pressure, forcing reabsorption. This is the exact opposite of the situation in the glomerulus - the pressures are switched and this is why the glomerulus favours filtration whereas the peritubular capillaries favour reabsorption

More than 90% of water, glucose (100%) and sodium are reabsorbed as well as 50% of the urea are reabsorbed in the tubule, mainly the proximal convoluted part

Urinary (13 decks)

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