Lecture 3 Glomerular Filtration

Question 1

What percentage of cardiac output does the kidney receive

Answer 1

20-25%

Question 2

If plasma constitutes 55% of BV and the kidney receives 1200ml/min of blood what is the renal plasma flow

Answer 2

55% of 1200mls/min

660mls/min

Question 3

What is the normal value for GFR

Answer 3

125mls/min

Question 4

If the renal plasma flow is 660mls/min and the GFR is 125mls/min what is the filtration fraction

Answer 4

125/660 x100 + 19% of the renal plasma becomes glomerular filtrate

Question 5

What is the glomerular filtrations dependent on

Answer 5

The balance of hydrostatic pressure and oncotic pressure (Starling’s forces)

Question 6

What are the 3 layers of the filtration membrane

Answer 6

Fenestration of glomerular endothelial cells (allows all through)
Basal lamina (prevents larger proteins)
Slit membrane between pedicles (prevents medium sized proteins)

Question 7

Why is glomerular capillary pressure higher in most of the capillaries in the body

Answer 7

Afferent arteriole is short and wide and offers little resistance to flow
So blood arriving at the glomerulus still has a high hydrostatic pressure

Question 8

How is the efferent arteriole different to the afferent

Answer 8

Long and narrow and offers a high post capillary resistance

Question 9

How do you calculate net filtration pressure

Answer 9

Hydrostatic pressure - Colloid osmotic pressure - fluid pressure created by fluid in Bowman’s capsule

Question 10

Name factors that affect the GFR

Answer 10

Glomerular capillary pressure
Sympathetic VC nervers
1. Sympathetic VC nerves  afferent and efferent constriction, greater sensitivity of afferent arteriole.
2. Circulating catecholamines  constriction 1ily afferent
3. Angiotensin II  constriction, of efferent at [low], both afferent and efferent at [high

Question 11

Why is the peri tubular capillaries able to reabsorb

Answer 11

Net result of low hydrostatic pressure and high oncotic pressure. Mainly at the proximal convoluted tubule

Question 12

What happens if you contract the afferent arteriole

Answer 12

Less pressure difference between the afferent and efferent so there will be a reduced filtration pressure and reduced blood flow

Question 13

Wha happens if you constrict the efferent arteriole

Answer 13

The pressure difference will be greatly increased and so the filtration pressure will increase and the blood flow will be reduced