regulation of arteriolar resistance

Question 1

what regulates arteriolar resistance?

Answer 1

haemodynamics
extrinsic effects
local (intrinsic) effects
special areas

Question 2

what controls TPR and therefore regulates MAP? (mean arterial pressure)

Answer 2

varying the radius of resistance vessels

Question 3

why is controlling the radius of arterioles so important?

Answer 3

Arteriolar radius affects flow through individual vascular beds, and mean arterial pressure
You cannot affect one without the other

Question 4

how do you achieve To keep the blood flow to each vascular bed sufficient, and keep mean arterial pressure in the right range

Answer 4

engage in some resistance juggling

Question 5

how do you achieve resistance juggling?

Answer 5

This is achieved by two levels of control over the smooth muscle surrounding arterioles:

Intrinsic mechanisms - concerned with meeting the selfish needs of each individual tissue

Extrinsic mechanisms – concerned with ensuring that the total peripheral resistance of the whole body stays in the right ball park

Question 6

how does sympathetic nerves have an impact on extrinsic control?

Answer 6

release norepinephrine
binds to 1-receptors
causes arteriolar constriction
therefore  flow through that tissue, and tends to  TPR

Question 7

what hormone controls extrinsic control?

Answer 7

Epinephrine
angiotensin II
vasopressin
atrial natriuretic peptide and brain natriuretic peptide

Question 8

where is Epinephrine released from?

Answer 8

released from adrenal medulla

Question 9

what does epinephrine bind to?

Answer 9

to 1-receptors

Question 10

what is the effect of epinephrine?

Answer 10

causes arteriolar constriction
therefore  flow through that tissue, and tends to  TPR

• but in some tissues, eg skeletal and cardiac
  muscle, it also activates 2-receptors
• causes arteriolar dilation
• therefore  flow through that tissue, and tends to  TPR

Question 11

whats the effect of angiotesnin II

Answer 11

produced in response to low blood volume
causes arteriolar constriction
therefore TPR

Question 12

whats the effect of vasopressin

Answer 12

released in response to low blood volume
causes arteriolar constriction
therefore TPR

Question 13

whats the effect of Atrial natriuretic peptide & Brain natriuretic peptide

Answer 13

released in response to high blood volume
causes arteriolar dilation
therefore  TPR

Question 14

what are the intrinsic controls of regulating arterioles?

Answer 14

Active (metabolic) hyperaemia
Pressure (flow) autoregulation
Reactive hyperaemia
4. The injury response

Question 15

what are the special areas that regulate arteriolar resistance?

Answer 15

Coronary circulation
Cerebral circulation
Pulmonary circulation
Renal circulation

Question 16

whats the effect of coronary circulation?

Answer 16

blood supply is interrupted by systole
but still has to cope with increased demand during exercise
shows excellent active hyperaemia
expresses many 2-receptors
these swamp any sympathetic arteriolar constriction

Question 17

whats the effect of cerebral circulation?

Answer 17

needs to be kept stable, whatever

shows excellent pressure autoregula

Question 18

whats the effect of pulmonary circulation?

Answer 18

decreaseO2 causes arteriolar constriction
ie the opposite response to most tissues
ensures that blood is directed to the best ventilated parts of the lung

Question 19

whats the effect of renal circulation

Answer 19

main function is filtration which depends on pressure
changes in MAP would have big effects on blood volume
shows excellent pressure autoregulation