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12. Year 2: 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?

25
What are examples of things that are not filtered well as the glomerular membrane?
26
What do the fenestrations (pores) of the glomerular basement prevent the filtration of?
Blood cells
27
What does the basal lamina of glomerulus prevent the filtration of?
Larger proteins
28
What do the slit membranes of the glomerulus between pedicles prevent the filtration of?
Medium sized proteins
29
What does PGC stand for?
Glomerular capillary pressure
30
Is glomerular capillary pressure higher or lower than most capillaries in the body, and why is this?
Higher: * Afferent arteriole is short and wide offering little resistance to flow * So blood arriving at glomerulus still has high hydrostatic pressure
31
How does the unique arranagement of efferent arterioles offer high post-capillary resistance?
They are long and narrow, unlike the afferent arterioles which are short and wide
32
How do the afferent and efferernt arterioles differ?
Afferent- short and wide Efferent - long and narrow
33
What is the golden rule of circulation in relation to high resistance areas?
* 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
Which of hydrostatic pressure and oncotic pressure is always favoured at gloermular capillaries?
Hydrostatic pressure which favours filtration
35
What is net filtration determined by?
* 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
What is the main factor that impacts GFR?
Main factor is PGC, which is dependent on the afferent and efferent arteriolar diameter and therefore the balance between them
37
What is PGC dependent on?
Afferent and efferent arteriolar diameter
38
GRF is subject to extrinsic control via?
* 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
How does sympathetic innervation impact the arterioles of the glomerular?
Causes afferent and efferent constriction, greater sensitivity of afferent arterioles
40
Is the afferent or efferent arterioles more sensitive to sympathetic vasoconstriction action?
Afferent
41
What effect does circulating catecholamines have on afferent/efferent arterioles of the glomerular?
Causes constriction of primary afferent
42
What effect does angiotensin II have on afferent/efferent arterioles of the glomerular?
* Causes constriction of efferent at low concentration and both afferent and efferent at high concentration
43
How does GFR change with PGC?
As PGC increases so does GFR
44
What is the autoregulatory range of GFR?
60-130mmHg (diagram is for a dog so has wrong values, but curve is the same shape)
45
Why is autoregulation of GFR important?
Means GFR is maintained over a wide range of blood pressures
46
How and when is autoregulation of GFR overridden?
* 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
How much extra blood can be provided to perfuse other organs when overridding GFR?
Up to 800ml/min
48
What does prolonged reduction in renal blood flow when overridding GFR autoregulation lead to?
* Prolonged reduction in renal BF can lead to irreparable damage which may lead to death because of disruption of kidneys role in homeostasis
49
What part of the kidney is responsible for reabsorption?
Peritubular capillaries
50
180L/day is filtered through glomerulus into the renal tubule, but how much of this is excreted as urine?
Only 1-2L/day
51
How is so much of the filtered fluid in the renal tubule able to be reabsorbed at the peritubular capillaries?
* 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
In the peritubular capillaries, is filtration or reabsorption entirely favoured?
Reabsorption (oncotic pressure is greater than hydrostatic pressure

12. Year 2: Urinary System (29 decks)

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