lecture 13 - intrinsic & extrinsic control of the circulation

Question 1

Which type of blood vessels are known as resistance vessels?

Answer 1

Small arteries and arterioles

Question 2

How do arterioles determine the volume that flows through the circulation?

Answer 2

By changing their radius by altering the vascular tone via smooth muscles

Question 3

What is vascular tone?

Answer 3

Tension exerted in a vessel by vascular smooth muscle cells, which regulates the radius of the vessel.

Question 4

How does vascular tone regulate mean arterial blood pressure?

Answer 4

By adjusting vessel tone, total peripheral resistance is adjusted, which is proportional to MABP

Question 5

What are the intrinsic mechanisms that control vascular tone?

Answer 5

myogenic response, paracrine factors (metabolites, NO), physical factors (temp., pressure)

Question 6

What are the extrinsic mechanisms that control vascular tone?

Answer 6

Vasodilator nerves, sympathetic nerves, endocrine factors (adrenaline, angiotensin, etc.)

Question 7

What is the myogenic response in terms of vascular tone regulation?

Answer 7

An intrinsic response where resistance vessels respond directly to a change in pressure by vasoconstricting or vasodilating.

Question 8

What mechanism prevents excess myogenic constriction in resistance vessels?

Answer 8

As vessel narrows in myogenic response, it generates shear stress which triggers the endothelium to produce NO, which has a local vasodilatory effect.

Question 9

How does metabolic regulation/active hyperemia regulate blood flow?

Answer 9

An organ’s metabolic activity causes a decrease in O2 and increase in metabolites, which trigger the release of local dilator substances to increase oxygenated blood flow to the organ.

Question 10

What is the difference between active and inactive hyperaemia, in terms of blood flow regulation?

Answer 10

Active hyperaemia is caused by normal metabolic processes that ‘use up’ oxygen, which reactive hyperaemia occurs when there is obstruction to blood flow and then metabolism continues downstream triggering vasodilation

Question 11

What are some of the vasoconstrictors produced by the endothelium of blood vessels?

Answer 11

Endothelin, Angiotensin II

Question 12

What are some of the vasodilators produced by the endothelium of blood vessels?

Answer 12

Nitric Oxide (NO), prostacyclin, adenosine

Question 13

What force typically causes the production of most of the nitrous oxide in endothelial cells in blood vessels?

Answer 13

Shear stress

Question 14

What factors typically increases shear stress in vessels and therefore increase NO production?

Answer 14

Atherosclerosis, exercise - cause narrowing of the vessels

Question 15

Which circulating hormones can trigger NO production?

Answer 15

Oestrogen, insulin

Question 16

Where do sympathetic vasoconstrivtor nerves terminate?

Answer 16

Tunica media, in strings of synaptic varicosities

Question 17

What neurotransmitter is used by sympathetic vasoconstrictor nerves?

Answer 17

Noradrenaline

Question 18

Which receptors in vascular myocytes are triggered by NA from sympathetic vasoconstrictor nerves?

Answer 18

alpha-adrenoceptors

Question 19

What occurs when alpha-adrenoceptors are triggered?

Answer 19

Vasoconstriction

Question 20

Where is the vasomotor centre, which controls vasoconstriction?

Answer 20

The brain stem

Question 21

How does venous cosntriction increase cardiac output?

Answer 21

Increases venous return, which increases end diastolic volume and therefore stroke volume and cardiac output

Question 22

How does capillary constriction increase end diastolic volume?

Answer 22

Contraction of resistance vessels causes interstitial fluid to be absorbed into the plasma, which increases EDV

Question 23

Does adrenaline cause vasoconstriction or vasodilation?

Answer 23

Vasodilation, via B2 receptors

Question 24

Does noradrenaline cause vasoconstriction or vasodilation?

Answer 24

Vasoconstriction via alpha receptors