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Year 1 Urinary > Glomerular Filtration lecture - Theo's and been through > Flashcards

Glomerular Filtration lecture - Theo's and been through Flashcards

1
Q

What does a fall in glomerular filtration lead to?

A

Renal Failure

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2
Q

What is Glomerular Filtration?

A

Passive process: fluid is ‘driven’ through the semipermeable (fenestrated) walls of the glomerular capillaries into the Bowmans capsule space by the hydrostatic pressure of heart.

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3
Q

What is meant by something is a ‘passive process’?

A

Doesn’t require ATP

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4
Q

Describe the filtration barrier?

A

The filtration barrier (fenestrated endothelium of capillaries and semipermeable Bowman’s capsule)

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5
Q

What is the barrier permeable to? (x2)

A

• fluids • small solutes (these are “freely filtered”: same concentration in filtrate and plasma)

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6
Q

What is it impermeable to? (x3)

A

• cells • proteins • drugs etc carried bound to protein

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7
Q

What drives Hydrostatic pressure?

A

Cardiac output

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8
Q

What is primary urine?

A

A clear fluid that is completely free from blood and proteins, is produced containing electrolytes and small solutes.

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9
Q

What is the difference of concentration of solutes in the filtrate vs the plasma in the Bowman’s capsule?

A

No difference

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10
Q

Pressure forcing filtrate out of capillary? Notation?

A

Hydrostatic pressure in glomerulus capillaries due to blood pressure = Pgc.

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11
Q

What are the opposing pressures to hydrostatic pressure (P gc)? (x2)

A

Hydrostatic pressure of Tubule (Pt) AND osmotic pressure of plasma proteins in the glomerular capillaries (Pi gc)

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12
Q

What values do you use to calculate the net ultrafiltration pressure (P uf)?

A

P uf = (P gc)- (P t)- (Pi gc)

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13
Q

What is the equation for Glomerular filtration Rate (GFR)?

A

GFR= (P uf) x (Kf)

(Remember, Puf = Pgc - Pt - Pigc).

Any changes in filtration forces or Kf will result in GFR imbalances. Kidney diseases may reduce number of functioning glomeruli = reduced surface area = dilation of glomerular arterioles by drugs/hormones.

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14
Q

What is Kf and what does it describe? (x2) What does this mean practically?

A

Where Kf is an ultrafiltration coefficient (membrane permeability and surface area available for filtration).

These two variables are mechanisms by which we can therefore change GFR without changing pressure.

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15
Q

How can surface area be changed in the kidneys (= change in GFR)? (x4)

A

Surface area is affected by number of functioning glomeruli (= reduced Kf), dilation of glomerular arterioles (= increased Kf) by drugs and hormones. Inflammation can also alter this.

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16
Q

SUMMARY: what can we change to alter GFR?

A
  • PRESSURE (Pgc, πgc, Pt).
  • Membrane permeability.
  • Surface area.

This all relates to the equation: GFR = (P uf) x (Kf)

(Remember, Puf = Pgc - Pt - Pigc).

17
Q

What is GFR?

A

• GFR = The amount of fluid filtered from the glomeruli into the Bowmans capsule per unit of time (ml/min). • Sum of filtration rate of all functioning nephrons

18
Q

What is normal GFR?

A

120ml/min

19
Q

How much of cardiac output enters kidneys? What term describes this?

A

20%, so 1L/min (because CO is 5L/min) = renal blood flow.

20
Q

What is approximate CO?

A

5L/min

21
Q

What proportion of blood is plasma?

A

60%

22
Q

What is the value for renal plasma flow approx.?

A

0.6L/min

23
Q

What is the filtration fraction approx.?

A

20% of plasma flow.

The proportion of the renal PLASMA flow that is filtered.

24
Q

What does GFR equal relative to Renal Plasma flow and Filtration Fraction?

A

GFR= Renal Plasma Flow x Filtration Fraction.

Renal blood flow = 1L/min
Renal plasma flow = 0.6L/min.
Filtration fraction = 20%.
THEREFORE, GFR = 0.6L/min x 0.2 = 120mL/min!

25
Q

What is the mechanism of autoregulation in the kidney called?

A

MYOGENIC AUTOREGULATION.

26
Q

What is the myogenic mechanism of autoregulation in the kidneys?

A

Vascular smooth muscle constricts when stretched. Keeps GFR constant when blood pressure rises.

Arterial pressure rises → afferent arteriole stretches → myogenic mechanism contracts the same afferent arteriole → (vessel resistance increases)→ blood flow reduces and GFR remains constant.

27
Q

What is the purpose of the myogenic mechanism of autoregulation in the kidneys?

A

During exercise, blood pressure increases. According to what we know already, this increases GFR. This doesn’t make sense functionally, because you dont want to urinate or lose lots of water in exercise.

Therefore, arteriole contraction in the kidneys reduces the surface area, which reduces Kf - compensating for the increase in Puf and therefore keeping GFR constant overall.

28
Q

How does Haemorrhage affect GFR?

A

Decrease in cardiac output, therefore decreasing GFR.

29
Q

How does obstruction in nephron affect GFR?

A

It increases tubular pressure, therefore decreases GFR.

Remember, tubular pressure, like osmotic pressure, is an opposing pressure to the hydrostatic pressure pushing filtrate into te Bowman’s capsule.

30
Q

How does reduced plasma protein affect GFR?

A

Decrease of opposing osmotic pressure, thereby increasing GFR.

31
Q

How does a small increase in blood pressure affect GFR?

A

It doesn’t affect GFR because of myogenic autoregulation.

32
Q

What is renal clearance?

A

Clearance is the number of litres of plasma that are completely cleared of the substance per unit time.

33
Q

What is the equation for renal clearance?

A

Clearance of urine = (Concentration of substance in urine (U))x(Rate of urine production (V))/(Concentration of substance in plasma (P)).

Units are in mL/min.

Note: you don’t need to change units for concentration of P and U if they are BOTH the same, because are measuring the relative proportions to eachother: U/P.

e.g. for Na+: suppose P = 145mM, U = 290mM, V = 1ml/min.

Therefore, renal clearance of Na+ = 290/145 x 1 = 2mL/min.

34
Q

What is Creatinine?

A
  • a waste product from creatine in muscle metabolism
  • amount of creatinine released is fairly constant
  • if renal function stable, amount creatinine in urine is stable
  • low values of creatinine clearance may indicate renal failure
  • high plasma creatinine may indicate renal failure

Rate of creatinine clearance = GFR

35
Q

What causes high plasma creatinine? (x3)

A

Protein shakes (temporarily), Muscular person, Renal Failure.

36
Q

What can renal clearance of PAH (Para aminohippurate)

A

Plasma Renal Flow

37
Q

What does amount excreted equal?

A

Amount Excreted = Amount filtered – amount reabsorbed +namount secreted

38
Q

SUMMARY: what can be determined about a substance if it’s excretion rate is below, the same as, and above 120mL/min? (And clinical application?)

[CLUE: normal GFR = 120mL/min].

A

Photo –>

39
Q

What happens in the plasma if GFR falls?

A

Excretory products build up in plasma.

Year 1 Urinary (8 decks)

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