Lecture 3 - Filtration

Question 1

What does filtration in the kidneys essentially produce?

Answer 1

A protein free filtrate of plasma

Question 2

What is the GFR?

Answer 2

Glomerular filtration rate

Question 3

What is the average GFR a day?

Answer 3

180L/day

Question 4

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

Answer 4

Filtration
Reabsorption
Secretion

Question 5

How much blood flows through the kidneys every min?

Answer 5

~1200mls (20-25% of CO)

Question 6

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

Answer 6

<5 mins

Question 7

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

Answer 7

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

Question 8

What is the normal GFR?

Answer 8

125mls/min

Question 9

How do you work out renal plasma flow?

Answer 9

Plasma is ~55% of total BV

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

Question 10

What is the filtration fraction?

Answer 10

Is the amount of renal plasma that becomes glomerular filtrate

Question 11

What is glomerular filtration dependent on?

Answer 11

Balance between hydrostatic forces favouring filtration and oncotic pressure favouring reabsorption

Question 12

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

Answer 12

Molecular size
Electrical charge
Shape

Question 13

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

Answer 13

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

Question 14

What does fenestrated epithelium prevent?

Answer 14

Filtration of RCCs

Question 15

What does the basal lamina prevent?

Answer 15

Filtration of larger proteins

Question 16

What does the slit membrane between pedicles prevent?

Answer 16

Filtration of medium sized proteins

Question 17

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

Answer 17

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

Question 18

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

Answer 18

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

Question 19

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

Answer 19

So that only filtration occurs at the glomerular capillaries

Question 20

What is the primary factor affecting the GFR in physiology?

Answer 20

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

Question 21

How does sympathetic stimulation affect the afferent and efferent arterioles?

Answer 21

Constricts both but greater sensitivity of afferent arteriole

Question 22

How do circulating catecholamines affect the afferent and efferent arterioles?

Answer 22

Constrict primarily the afferent arteriole

Question 23

How does angiotensin II affect the afferent and efferent arterioles?

Answer 23

Low levels - efferent only

High levels - efferent and afferent

Question 24

Describe the effect on GFR in the following scenario:

Afferent arteriolar constriction

Answer 24

Decreased GFR

Question 25

Describe the effect on GFR in the following scenario: | Efferent arteriolar constriction

Answer 25

Increased GFR

Question 26

Describe the effect on GFR in the following scenario: | Afferent arteriolar dilatation

Answer 26

Increased GFR

Question 27

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

Answer 27

Autoregulation

Question 28

Over what MBP is autoregulation effective?

Answer 28

60-130mmHg | below this filtration falls and ceases altogether below 50mmHg

Question 29

What happens in the kidneys if mean arterial pressure increases?

Answer 29

Automatic increase in arterial arteriolar constriction preventing a rise in PGC (also dilates if BP falls)

Question 30

Does autoregulation of the kidneys rely on nerves or hormones?

Answer 30

Neither

Question 31

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

Answer 31

Where BP faces serious compromise, e.g. haemorrhage | Activates sympathetic nerves which liberates more blood for immediately more improtant organs

Question 32

What can prolonged reduction in renal blood flow lead to?

Answer 32

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

Question 33

What is the hydrostatic pressure in the peritubular capillaries like?

Answer 33

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

Question 34

Where is >99% of the filtrate reabsorbed?

Answer 34

Peritubular capillaries

Question 35

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

Answer 35

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

Question 36

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

Answer 36

20%

Question 37

Why is reabsorption favoured in the peritubular capillaries?

Answer 37

As oncotic pressure is greater than hydrostatic pressure

Question 38

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

Answer 38

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