11 - Regulation of the CVS

Question 1

Give the equation to calculate mean systemic arterial pressure

Answer 1

Mean BP = CO x TPR

Mean systemic arterial pressure = cardiac output x total peripheral resistance

Question 2

Give 4 factors that affect venous volume distribution

Answer 2

• peripheral venous tone
• gravity
• skeletal muscle pump
• breathing

Question 3

What determines venous return to the heart?

Answer 3

central venous pressure

Question 4

State Starling’s Law (with reference to the heart)

Answer 4

the amount of blood returning to the heart (venous return) determines the stroke volume

Question 5

Which vessels mainly determine flow control?

Answer 5

arterioles (change constriction- this is affected by the number of adrenoreceptors)

Question 6

What are the 3 mechanisms of regulating blood flow

Answer 6

• local mechanisms (intrinsic)
• hormonal (extrinsic)
• autonomic nervous system (extrinsic)

Question 7

Define autoregulation

Answer 7

the intrinsic capacity to compensate for changes in perfusion pressure by changing vascular resistance
(i.e. to maintain the flow even if the pressure changes)

Question 8

When BP drops, what happens to resistance and flow?

Answer 8

there is a gradual decrease in resistance and hence, a gradual increase in flow

Question 9

How does injury change autoregulation?

Answer 9

when a vessel is injured, platelets aggregate and release serotonin, which is a powerful vasoconstrictor

Question 10

State two molecules produced in the endothelium that cause vasodilation.

Answer 10

NO and prostacyclin

Question 11

What is the role of kinins?

Answer 11

vasodilators

Question 12

What does ANP stand for?
What are they?
Where are they produced?

Answer 12

Atrial Natriuretic Peptide
vasodilators
released from the cardiac atria as they stretch

Question 13

Give the name of 3 circulating vasconstrictors

Answer 13

vasopresssin (released from the posterior pituitary)
angiotensin II
noradrenaline

Question 14

What is the length of the nerves in the parasympathetic nervous system?

Answer 14

long preganglionic fibre

short postganglionic fibre

Question 15

Which vessels to sympathetic nerve fibres not innervate?

Answer 15

capillaries (and precapillary sphincters and some metarterioles)

Question 16

How does the sympathetic nervous system effect blood vessels?

NOTE: there is not much parasympathetic innervation of the vascular system

Answer 16

causes vasoconstriction

Question 17

What are the 3 areas of the Vasomotor Centre?

Answer 17

• vasocontrictor area (pressor)
• vasodilator area (depressor)
  cardioregulatory inhibitory area

Question 18

Which areas of the brain can effect the VMC?

Answer 18

higher centres in the brain (e.g. hypothalamus)

NOTE: this allows an anticipatory response to exercise i.e. the ventilation rate will go up slightly before exercise

Question 19

What do the lateral portions of the VMC control?

Answer 19

control heart activity by influencing heart rate and contractility

Question 20

What do the medial portions of the VMC control?

Answer 20

transmit signals via the vagus nerve to the heart that decreases heart rate

Question 21

What innervation do the blood vessels receive?

Answer 21

sympathetic post-ganglionic innervation

NOTE MUCH PARASYMPATHETIC INNERVATION OF THE VASCULAR SYSTEM

Question 22

There is always some tonic activity- at baseline, there is a certain frequency of impulses which maintain vasomotor tone. What happens when the frequency of this nerve traffic increases or decreases?

Answer 22

increases - constriction

decrease - dilation

Question 23

What systems innervate the heart rate?

Answer 23

sympathetic and parasympathetic (DUAL INNERVATION)

to the sinoatrial node

Question 24

What is normal resting HR?

Answer 24

70 bpm

Question 25

Give the mechanism of the parasympathetic pathway

Answer 25

acetylcholine deacreases the gradient of the pacemaker potential (so the potential takes longer to reach threshold and fire)

Question 26

Give the mechanism of the sympathetic pathway

Answer 26

adrenaline and noradrenaline increase the gradient of the pacemaker potential so the threshold is reached even more quickly