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Renal/Urology > Lecture 3 - Filtration > Flashcards

Lecture 3 - Filtration Flashcards

1
Q

What does filtration in the kidneys essentially produce?

A

A protein free filtrate of plasma

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2
Q

What is the GFR?

A

Glomerular filtration rate

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3
Q

What is the average GFR a day?

A

180L/day

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4
Q

What are the 3 main processes that go on in the kidneys?

A

Filtration
Reabsorption
Secretion

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5
Q

How much blood flows through the kidneys every min?

A

~1200mls (20-25% of CO)

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6
Q

In less than how many minutes does the blood volume equal to the total BV pass through the kidneys?

A

<5 mins

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7
Q

How many red bloods are filtered through Bowman’s capsule?

A

NONE!!
Most of the plasma and all the RCCs pass into efferent arterioles and into the peritubular capillaries, then into the renal vein

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8
Q

What is the normal GFR?

A

125mls/min

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9
Q

How do you work out renal plasma flow?

A

Plasma is ~55% of total BV

55% of 1200mls/min = 660mls/min

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10
Q

What is the filtration fraction?

A

Is the amount of renal plasma that becomes glomerular filtrate

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11
Q

What is glomerular filtration dependent on?

A

Balance between hydrostatic forces favouring filtration and oncotic pressure favouring reabsorption

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12
Q

What things determine the filterability of solutes across Bowmen’s capsule?

A

Molecular size
Electrical charge
Shape

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13
Q

What are the three layers of the filtration membrane in the kidneys?

A
  1. Fenestrated epitheliium
  2. Basal lamina of glomerulus
  3. Slit membrane between pedicles
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14
Q

What does fenestrated epithelium prevent?

A

Filtration of RCCs

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15
Q

What does the basal lamina prevent?

A

Filtration of larger proteins

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16
Q

What does the slit membrane between pedicles prevent?

A

Filtration of medium sized proteins

17
Q

Why is glomerular capillary pressure greater than most of the capillaries in the body?

A

Afferent arteriole is short and wide and offers little resistance to flow (so blood arriving at glomerulus has high hydrostatic force)
Efferent arteriole long and narrow + so offers high post capillary resistance

18
Q

What is the golden rule of circulation when it comes to hydrostatic pressure?

A

If you high resistance, hydrostatic pressure upstream is increased while pressure downstream is decreased

19
Q

Why is it essential that hydrostatic pressure is greater than oncotic pressure at the glomerulus?

A

So that only filtration occurs at the glomerular capillaries

20
Q

What is the primary factor affecting the GFR in physiology?

A

The glomerular capillary pressure which is determined by the diameter of the afferent and efferent arterioles

21
Q

How does sympathetic stimulation affect the afferent and efferent arterioles?

A

Constricts both but greater sensitivity of afferent arteriole

22
Q

How do circulating catecholamines affect the afferent and efferent arterioles?

A

Constrict primarily the afferent arteriole

23
Q

How does angiotensin II affect the afferent and efferent arterioles?

A

Low levels - efferent only

High levels - efferent and afferent

24
Q

Describe the effect on GFR in the following scenario:

Afferent arteriolar constriction

A

Decreased GFR

25
Q

Describe the effect on GFR in the following scenario:

Efferent arteriolar constriction

A

Increased GFR

26
Q

Describe the effect on GFR in the following scenario:

Afferent arteriolar dilatation

A

Increased GFR

27
Q

What is the process of the renal vasculature instrinsically adjusting its resistance in response to BP?

A

Autoregulation

28
Q

Over what MBP is autoregulation effective?

A

60-130mmHg

below this filtration falls and ceases altogether below 50mmHg

29
Q

What happens in the kidneys if mean arterial pressure increases?

A

Automatic increase in arterial arteriolar constriction preventing a rise in PGC

(also dilates if BP falls)

30
Q

Does autoregulation of the kidneys rely on nerves or hormones?

A

Neither

31
Q

In which situations may autoregulation of the kidneys be overriden? Why is this? How is it done?

A

Where BP faces serious compromise, e.g. haemorrhage

Activates sympathetic nerves which liberates more blood for immediately more improtant organs

32
Q

What can prolonged reduction in renal blood flow lead to?

A

Irreparable damage which may lead to death due to disruption in kidneys role in haemostasis

33
Q

What is the hydrostatic pressure in the peritubular capillaries like?

A

Hydrostatic pressure is very low as the efferent arteriole offers resistance along its entire length
So this favours reabsorption in the peritubular capillaries

34
Q

Where is >99% of the filtrate reabsorbed?

A

Peritubular capillaries

35
Q

Why is oncotic pressure higher in the efferent tubule and peritubular capillaries higher?

A

20% of plasma has been filtered out so this concentrates plasma proteins

36
Q

What % of plasma is filtered out in the Bowmen’s capsule?

A

20%

37
Q

Why is reabsorption favoured in the peritubular capillaries?

A

As oncotic pressure is greater than hydrostatic pressure

38
Q 
What percentage of:
Water
Glucose
Na
Urea
Filtered at the glomerulus are reabsorbed within the tubule (mainly PCT)?
A

Water - 99.5%
Glucose - 100%
Na - 99.5%
Urea - 50%

Renal/Urology (29 decks)

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