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Block 1 Week 4 > Glomerular Filtration > Flashcards

Glomerular Filtration Flashcards

1
Q

Which arteries give off the afferent arterioles which enter the renal corpuscle?

A

Interlobular arteries.

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2
Q

How is urinary excretion rate calculated?

A

Filtration rate + Secretion rate - Reabsorption rate.

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3
Q

What percentage of cardiac output does the kidney receive?

A

20%.

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4
Q

What is the approximate renal blood flow per minute?

A

1 litre.

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5
Q

What is the approximate renal plasma flow per minute?

A

600ml.

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6
Q

Approximately what percentage of renal plasma flow passes through the filtration barrier to form filtrate? How many ml will this be?

A

20% of the 600ml of plasma flow, which will make it 120ml/minute.

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7
Q

Does albumin have a positive or negative charge?

A

Negative.

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8
Q

Define GFR.

A

The volume of filtrate formed by all the nephrons in both kidneys per unit time.

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9
Q

What is the GFR calculation?

A

GFR = Kf x NFP

Kf = Glomerular capillary filtration coefficient 
NFP = Net filtration pressure
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10
Q

What are the components of the Kf (glomerular capillary filtration coefficient)?

A
  1. Surface area available for filtration

2. Hydraulic conductivity (‘permeability’) of the filtration barrier

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11
Q

What are the components of the Net Filtration Pressure (NFP)?

A
  1. Sum of the hydrostatic pressures

2. Summ of the colloid osmotic (oncotic) pressures

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12
Q

Which way does the oncotic/osmotic pressure pull water in the renal capsule? Why?

A

Osmotic pressure is pulling water back into the glomerular side from Bowman’s capsule. This is because although the filtrate composition is similar to the plasma, the plasma contains proteins, but the filtrate doesn’t, so water moves by osmosis back to the glomerular capillaries.

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13
Q

What is a typical Net Filtration Pressure?

A

10 mmHg.

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14
Q

Give the equation for Net Filtration Pressure.

A

PG - PB - πG + πB

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15
Q

In normal physiology, what will the value of πB in the Net Filtration Pressure always be? Why is this?

A

0 - because there should be no osmotic movement of water from the glomerular capillaries into the Bowman’s capsule due to the presence of plasma proteins in the glomerulus.

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16
Q

What is the main component which varies to the greatest degree in GFR?

A

PG (hydrostatic glomerular pressure).

17
Q

What is PG (hydrostatic glomerular pressure) dependent on?

A
  1. Arterial pressure
  2. Afferent arteriole resistance
  3. Efferent arteriole resistance
18
Q

What is the general rule in relation to whether GFR will increase or decrease in relation to constriction and dilation of the afferent and efferent arterioles?

A

AA dilates and/or the EA constricts - GFR will increase

AA constricts and/or EA dilates - GFR will decrease

19
Q

How does the presence of Angiotensin 2 affect GFR?

A

It preferentially constricts the efferent arteriole (EA) - therefore increasing PG (hydrostatic glomerular pressure), therefore increasing GFR.

20
Q

How do prostaglandins affect GFR?

A

They vasodilate the afferent arteriole (AA) - therefore increasing PG, therefore increasing GFR.

21
Q

How does the presence of atrial natriuretic peptide (ANP) affect GFR?

A

It vasodilates the afferent arteriole (AA) - therefore increasing PG, therefore increasing GFR.

22
Q

How does the presence of noradrenaline, adenosine, and endothelin affect GFR?

A

They tend to vasoconstrict AA - therefore decreasing PG, therefore reducing GFR.

23
Q

Where does blood enter once it passes through the efferent arteriole?

A

The peritubular capillaries.

24
Q

Which factors make absorption rather than filtration favoured in the peritubular capillaries?

A
  1. Lower hydrostatic pressure - making it easier for fluid to move back into the peritubular capillaries.
  2. Higher colloid osmotic pressure - high protein concentration osmotically draws water into the peritubular capillaries.
25
Q

Which mechanisms are responsible for the auto-regulation of GFR?

A
  1. Myogenic response

2. Tubuloglomerular feedback

26
Q

What is the Myogenic response in regulation of GFR?

A

The inherent ability of smooth muscle in afferent arterioles to respond to changes in vessel circumference by contracting or relaxing.

27
Q

Describe how the myogenic response would control GFR in response to an increase in arterial blood pressure.

A
  1. Increase in arterial blood pressure.
  2. Increased renal blood flow and increased GFR.
  3. Stretching of AA smooth muscle cells.
  4. Opens Ca2+ channels.
  5. Reflex contraction of AA smooth muscle.
  6. Vasoconstriction of AA.
  7. Increased resistance to flow.
  8. Prevents changes in renal blood flow and GFR.
28
Q

How does the tubuloglomerular feedback mechanism in GFR regulation work?

A

It allows changes in the tubule lumen to control the AA resistance (glomerulus) in the same nephron.

29
Q

In the Juxtaglomerular Apparatus, what specifically is being sensed by the Macula Densa cells?

A

Sodium Chloride (NaCl).

30
Q

When arterial blood pressure is increased/decreased, how will this affect the amount of NaCl in the proximal part of the distal convoluted tubule?

A
  • When arterial blood pressure increases, there will be a transient increase in GFR, which increases flow and NaCl delivered to the distal tubule.
  • When arterial blood pressure decreases, there will be a transient decrease in GFR, which decreases flow and NaCl delivered to the distal tubule.
31
Q

Describe how tubuloglomerular feedback would control GFR in response to an increase in arterial blood pressure.

A
  1. Increase in arterial blood pressure.
  2. Increased renal blood flow and increased GFR.
  3. Increased NaCl delivered to macula densa cells.
  4. Release of paracrine factors (e.g. adenosine).
  5. Constriction of AA smooth muscle.
  6. Vasoconstriction of AA.
  7. Increased resistance to flow.
  8. Restores renal blood flow and GFR.
32
Q

What is a limitation of using GFR to look at kidney health?

A

It does not tell you the cause or location of the problem.

Block 1 Week 4 (5 decks)

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