Peripheral Resistance

Question 1

Most important factor in determining resistance

Answer 1

Arteriolar diameter

Question 2

Factors affecting blood vessel radius

Answer 2

Active tension exerted by smooth muscle
Passive elastic properties of wall (elastin & collagen)
BP Inside vessel

Question 3

Formula for Distending Pressure

Answer 3

Wall tension/Radius

Question 4

Formula for wall tension

Answer 4

Pressure x Radius

Question 5

Compare wall tension of capillaries and aorta and why

Answer 5

Tw is much higher in aorta than capillaries to avoid wall damage

As result of smaller radius (Tw= P x r)

Question 6

What does an increase in vessel radius cause in terms of tension

Answer 6

An increase in wall tension (e.g. aneurysm)

Question 7

What part of vessels controls radius

Answer 7

Smooth muscle is responsible for developing tension

Question 8

Importance of active control of vessel calibre

Answer 8

This allows:
Redistribution of blood flow
Control of pre/post capillary sphincters
Regulation of vascular tone and control of blood pressure

Question 9

What happens to active tension and passive tension during vasoconstriction

Answer 9

Increased active tension

Decreased passive tension

Question 10

What happens to active tension and passive tension during vasodilatation

Answer 10

Decreased active tension

Increased passive tension

Question 11

What does vasoconstriction do to blood vessels

Answer 11

SM contracts and lumen is smaller

Greater resistance

Question 12

Effect of Sympathetic nervous system on blood vessel dilation

Answer 12

Neurotransmitters released via vesicles (mainly NA)

Alpha1 adrenoceptor activation by NA causes vasoconstriction (most important)

Same with a2

Beta2 on SM stimulation causes vasodilatation

KEY TAKEAWAY - GENERALISED INCREASE IN SYMPATHETIC ACTIVITY, THERE IS VASOCONSTRICTION (a1) IN MOST NERVES; INCREASE IN RESISTANCE AND BP

Question 13

Hormones affecting vascular smooth muscle contraction

Answer 13

Catecholamines
- Noradrenaline
- Adrenaline
(constrict/dilate)

Peptides

• Vasopressin, Angiotensin (constrict)
• Bradykinin

Question 14

Intrinsic Mechanisms causing vasorelaxation/vasodilation

Answer 14

PGI2 - Prostacyclin
NO - Nitric Oxide
EDHF - Endothelium-derived hyperpolarising factor (mostly pathological i think)

Question 15

What changes in CO2 and O2 cause vasodilation and vasoconstriction in systemic vasculature

Answer 15

Low O2 and high CO2 as result of high metabolic activity

Question 16

What changes in CO2 and O2 cause vasodilation and vasoconstriction in pulmonary vasculature

Answer 16

Question 17

Effect of lactate, H+, K+ and adenosine changes on blood vessel calibre

Answer 17

Question 18

Response of blood vessels to stretch as result of increased BP - Autoregulation of blood flow

Answer 18

Body compensates with vasoconstriction to increase resistance to compensate increased driving force so that flow remains constant

Question 19

What happens to autoregulation if BP gets too high/low

Answer 19

If BP leaves the autoregulatory range, the blood loses the ability to effectively autoregulate and flow increases/decreases unnecessarily

Question 20

Extrinsic control mechanisms involved with regulation of arterial BP

Answer 20

Nerves, hormones