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Urinary System > Glomerular Filtration > Flashcards

Glomerular Filtration Flashcards

1
Q

What are the basic renal processes?

A

Filtration

Reabsorption

Excretion

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2
Q

What is filtration?

A
  • The formation at the glomerular capillaries of an essentially protein-free filtrate of plasma (20% of total plasma volume)
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3
Q

What percentage of total plasma volume if the filtrate?

A

20%

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4
Q

What is GFR/day?

A

180L/day

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5
Q

What is the advantage of GFR being so high (180L/day)?

A

Allows kidneys to regulate ECF volume and composition and eliminate any ‘nasty’ substances

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6
Q

What is reabsorption?

A
  • Substances that the body wants are reabsorbed, those that it doesn’t want stay in the tubule and are excreted
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7
Q

What is secretion?

A

Substances may be specifically removed from the body in this way

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8
Q

What blood flow does the kidney receive in ml/min?

A

About 1200ml/min

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9
Q

What percentage of cardiac output (CO) does the kidneys recieve?

A

20-25%

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10
Q

What does CO stand for?

A

Cardiac output

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11
Q

Explain how the kidneys have almost the highest BF/g tissue of any tissue in the body?

A

They weight less than 1% of body weight (BW) but recieve 20-25% of cardiac output (CO)

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12
Q

What does BW stand for?

A

Body weight

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13
Q

What are examples of things that are not affected by filtration into the Bowman’s capsule and carry on to the efferent arterioles into the peritubular capillaries then renal vein?

A

None of RBCs and only a fraction of plasma

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14
Q

Where do red blood cells go onces they pass by the Bowman’s capsule via the afferent arteriole?

A

Efferent arterioles -> peritubular capillaries -> renal vein

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15
Q

What does BV stand for?

A

Blood volume

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16
Q

What percentage of blood volume does plasma account for?

A

About 55%

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17
Q

What is the renal plasma flow in ml/min?

A

660ml (55% of 1200ml)

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18
Q

What is normal GFR in ml/min?

A

125ml/min

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19
Q

What is the filtration fraction?

A

Amount of renal plasma that becomes glomerular filtrate on passing by

125 (normal GFR) / 660 (normal renal plasma flow x 100 = 19%

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20
Q

Glomerular filtration works the exact same way as fluid filteres out of any capillary bed in the body, what does this mean?

A

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

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21
Q

Do hydrostatic forces favour filtration or reabsorption?

A

Filtration

22
Q

Do oncotic pressure forces favour filtration or reabsorption?

A

Reabsorption

23
Q

What are some things that permselectivity of the glomerular barrier depends on?

A
  • Molecular size
  • Electrical charge
  • Shape
24
Q

What are examples of things that are completely filtrated at glomerular barrier?

A
25
Q

What are examples of things that are not filtered well as the glomerular membrane?

A
26
Q

What do the fenestrations (pores) of the glomerular basement prevent the filtration of?

A

Blood cells

27
Q

What does the basal lamina of glomerulus prevent the filtration of?

A

Larger proteins

28
Q

What do the slit membranes of the glomerulus between pedicles prevent the filtration of?

A

Medium sized proteins

29
Q

What does PGC stand for?

A

Glomerular capillary pressure

30
Q

Is glomerular capillary pressure higher or lower than most capillaries in the body, and why is this?

A

Higher:

  • Afferent arteriole is short and wide offering little resistance to flow
  • So blood arriving at glomerulus still has high hydrostatic pressure
31
Q

How does the unique arranagement of efferent arterioles offer high post-capillary resistance?

A

They are long and narrow, unlike the afferent arterioles which are short and wide

32
Q

How do the afferent and efferernt arterioles differ?

A

Afferent- short and wide

Efferent - long and narrow

33
Q

What is the golden rule of circulation in relation to high resistance areas?

A
  • If you have high resistance, hydrostatic pressure upstream is increased and pressure downstream is decreased
  • This means both afferent and efferent arterioles contribute to a very high PGC
34
Q

Which of hydrostatic pressure and oncotic pressure is always favoured at gloermular capillaries?

A

Hydrostatic pressure which favours filtration

35
Q

What is net filtration determined by?

A
  • Hydrostatic pressure (blood pressure)
  • Colloid osmotic pressure due to plasma but not in Bowman’s capsule
  • Pressure created by fluid in Bowman’s capsule
36
Q

What is the main factor that impacts GFR?

A

Main factor is PGC, which is dependent on the afferent and efferent arteriolar diameter and therefore the balance between them

37
Q

What is PGC dependent on?

A

Afferent and efferent arteriolar diameter

38
Q

GRF is subject to extrinsic control via?

A
  • Sympathetic VC nerves
    • Cause afferent and efferent constriction, greater sensitivity of afferent arteriole
  • Circulating catecholamines
    • Cause constriction of 1°ily afferent
  • Angiotensin II
    • Causes constriction of efferent at low concentration and both afferent and efferent at high concentration
39
Q

How does sympathetic innervation impact the arterioles of the glomerular?

A

Causes afferent and efferent constriction, greater sensitivity of afferent arterioles

40
Q

Is the afferent or efferent arterioles more sensitive to sympathetic vasoconstriction action?

A

Afferent

41
Q

What effect does circulating catecholamines have on afferent/efferent arterioles of the glomerular?

A

Causes constriction of primary afferent

42
Q

What effect does angiotensin II have on afferent/efferent arterioles of the glomerular?

A
  • Causes constriction of efferent at low concentration and both afferent and efferent at high concentration
43
Q

How does GFR change with PGC?

A

As PGC increases so does GFR

44
Q

What is the autoregulatory range of GFR?

A

60-130mmHg

(diagram is for a dog so has wrong values, but curve is the same shape)

45
Q

Why is autoregulation of GFR important?

A

Means GFR is maintained over a wide range of blood pressures

46
Q

How and when is autoregulation of GFR overridden?

A
  • When blood volume/BP face serious compromise such as in haemorrhage, activation of sympathetic VC nerves and AII can override autoregulation to liberate more blood for immediately important organs
  • As much as 800ml/min can be provided to perfuse these organs at the expense of the kidneys
  • However, prolonged reduction in renal BF can lead to irreparable damage which may lead to death because of disruption of kidneys role in homeostasis
47
Q

How much extra blood can be provided to perfuse other organs when overridding GFR?

A

Up to 800ml/min

48
Q

What does prolonged reduction in renal blood flow when overridding GFR autoregulation lead to?

A
  • Prolonged reduction in renal BF can lead to irreparable damage which may lead to death because of disruption of kidneys role in homeostasis
49
Q

What part of the kidney is responsible for reabsorption?

A

Peritubular capillaries

50
Q

180L/day is filtered through glomerulus into the renal tubule, but how much of this is excreted as urine?

A

Only 1-2L/day

51
Q

How is so much of the filtered fluid in the renal tubule able to be reabsorbed at the peritubular capillaries?

A
  • The unique efferent arteriole has important effects on Starling’s forces in peritubular capillaries to do this
    • It offers resistance along its entire length, so there is a large pressure drop so that hydrostatic is very low, PPC is about 15mmHg
    • Since 20% of plasma has filtered into Bowman’s capsule in glomerulus the blood remaining in the efferent arteriole and then the peritubular capillaries has a higher concentration plasma proteins \ ­Pp
    • So the net result of low PPC and high Pp is that Starling’s forces in the peritubular capillaries entirely favour reabsorption
    • Glomerulus is reabsorbed within the tubule, mainly at the proximal convoluted tubule
52
Q

In the peritubular capillaries, is filtration or reabsorption entirely favoured?

A

Reabsorption (oncotic pressure is greater than hydrostatic pressure

Urinary System (29 decks)

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