19. Control of Renal Circulation and Glomerular Filtration

Question 1

What effect does vasoconstriction have on blood flow to the kidneys?

Answer 1

Decreased blood flow

Question 2

How is GFR maintained constant?

Answer 2

By maintaining renal blood flow

Question 3

What MAP range does autoregulation of renal blood flow occur?

Answer 3

80-180 mmHg

Question 4

What do MAPs below 80 or above 180 result in?

Answer 4

Proportionate changes in flow

Question 5

What two mechanisms are used in the autoregulation of the kidneys?

Answer 5

Myogenic response

Tubuloglomerular feedback

Question 6

What is the myogenic response?

Answer 6

Increase in pressure causes stretching of vessels walls

This causes a reflex contraction of the smooth muscle

Question 7

What is tubuloglomerular feedback?

Answer 7

Change in RBF and GFR lead to a change in rate of fluid flow through tubules
Macula densa cells cause a change in afferent arteriolar tone

Question 8

Where is the macula densa?

Answer 8

Point where the thick ascending loop of Henle meets the distal convoluted tubule
Nephron is folded so that MD is very close to the afferent arteriole

Question 9

What are the steps in tubuloglomerular feedback?

Answer 9

1. Increased pressure in afferent arteriole=increased GFR= increased tubular flow rate
2. Increased delivery of Na+/Cl- to macula densa, increasing uptake by MD cells
3. Activates a cation channel which allows calcium entry that causes MD to release adenosine or ATP
4. Diffuses to afferent arteriole
5. AA constriction and renin release
6. RBF and GFR return to normal

Question 10

What mediators are released to stimulate renin and vasodilation?

Answer 10

PGE2

NO

Question 11

What is the advantage of autoregulating GFR and RBF over the 80-180 mmHg range?

Answer 11

Small fluctuations in BP do not respond in fluctuations of RBF and GFR
Protects fragile glomerular capillaries against increases in perfusion pressure

Question 12

What brings about changes in RBF and GFR?

Answer 12

Extrinsic mechanisms mediated by nerves and hormones

Question 13

What is the nervous control of RBF and GFR?

Answer 13

Arterioles are innervated by sympathetics
NA causes vasoconstriction
Reduction in RBF and GFR

Question 14

What is the hormonal control of RBF and GFR?

Answer 14

Adrenaline and Angiotensin 2 cause vasoconstriction

Question 15

What is the effect of severe exercise, pain, severe emotional stimuli on RBF and GFR?

Answer 15

Sympathetic activity in vessels
Adrenaline released from adrenal medulla
Vasoconstriction
GFR decreases

Question 16

What dampens the vasoconstrictor effects on the afferent arterioles of the SNS and angiotensin 2?

Answer 16

Prostaglandins PGE2, PGI2

Question 17

What stimulates prostaglandin synthesis?

Answer 17

Ischaemia
SNS
Angiotensin 2

Question 18

What influences passage through Bowman’s capsule?

Answer 18

Molecular size
Charge (negatively charged are restricted)
Molecular shape (rigid ones don't pass as well)