Glomerular Filtration

Question 1

How much of the plasma is filtered at the Kidneys Bowmans capsule

Answer 1

20% is the filtration fraction

Question 2

What is the normal glomerular filtrate rate

Answer 2

180L/day

125mls/min

Question 3

How do we work out the filtration fraction

Answer 3

Kidneys receive 20-25% total cardiac out put which is 1200mls/min

plasma constitutes to 55% total blood volume

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

GFR is normally 125mls/min

125/660 x 100 = 20%

Question 4

How does filtration occur at the glomerulus

Answer 4

Because of the high pressure in the glomerulus,

Due to the afferent arteriole offers little resistance, but the efferent arteriole offer high post capillary resistance

This build up creates a strong hydrostatic pressure

So the high pressure favouring filtration exceed the pressure in the glomerulus (osmotic pressure gradient)

so filtration occurs

Question 5

What determines the filterability of solutes across the glomerulus

Answer 5

The peremselectivity of the glomerular barrier

Due to the filtration memebrane

• Fenestrations (pore) of glomerular endothelial cells
• Basal lamina of glomerulus
• still membrane between pedicles

Question 6

What is the filterability of the the fenestrations of the glomerular endothelial cells

Answer 6

Prevent filtration of blood cells but allow all components of blood plasma to pass through

Question 7

What is the filterability of the basal lamina of the glomerulus

Answer 7

Prevents the filtration of larger proteins

Smaller molecular proteins can still pass through

Question 8

What is the filterability of the still membrane between pedicles

Answer 8

Prevents filtration of medium sized proteins

lowest exclusion

Question 9

What substances are filtered through the glomerulus

Answer 9

na+
K+ 
Cl- 
H2O 
Urea 
Glucose 
Sucrose 
polythene glycol 
insulin

Question 10

What layers the visceral layer of the bowmans capsule, what is its function

Answer 10

Podocytes

form a filtration barrier, cooperate with mesangial cells to support the structure and function of the glomerulus

Question 11

What is the purpose of autoregulation of the glomerulus,

Answer 11

Intrinsic ability eg when the arterial blood pressure increases to adjust resistance, causing afferent arteriolar constriction to keep blood flow and GFR essential constant

(same in reverse occurs when blood pressure decreases)

Question 12

What does the auto-regulation of the glomerulus ensure

Answer 12

The GFR is maintained constant over a wide range of mean blood pressure

Question 13

What is the auto-regulatory range, what occurs below this range

Answer 13

60 - 130mmHg

Below 60 - filtration falls

Below 50 - filtration ceases

Question 14

What three factors subject extrinsic control of the pressure of the glomerular capillaries

Answer 14

Sympathetic vasoconstrictor nerves
- constrict afferent and efferent arteriolar

Circulating catecholamines
- constrict afferent arteriolar

Angiotensin II

Question 15

What is basically crucial in determining the GRF

Answer 15

The relative diameter of afferent and efferent arteriolar, as affects the balance of resistance therefore the pressure of the glomerular capillaries

Question 16

What occurs when afferent arteriole constricts

Answer 16

Increases resistance in afferent arteriole, so there is decreased blood flow to the kidney, so pressure in glomerulus decreases therefore GFR decreases

Question 17

What occurs when the efferent arteriole constricts

Answer 17

Increases resistance in the efferent arterioles, so pressure in the glomerulus increases as causes a build up blood in the glomerulus, therefore GFR increases

Question 18

What is the effect of angiotensin on the glomerulus, at high and low concentrations

Answer 18

Low angiotensin concentration - Constriction of efferent arteriolar

High concentrations
- Constriction of both afferent and efferent arteriolar

Question 19

When does interactions of extrinsic and intrinsic control occur in the glomerulus

Answer 19

Occurs in situations where blood volume/ blood pressure face serious compromise eg haemorrhage

Continual Physical activity eg marathons

Question 20

What is the affect on the kidney when there is a serious decreases in blood volume eg haemorrhage

Answer 20

Activation of sympathetic vasoconstrictor nerves, override auto-regulation, this liberates blood for more immediately important organs at the expense of the kidney