L12 Regulation of Vascular function

Question 1

Where is the greatest change of vascular resistance able to be had in the vascular tree and where is the least

Why

Answer 1

The precapillary vessels (small arteries/arterioles) because they have proportionally greater thickness of the SM in tunica media

Post-capillary vessels have smaller proportion of VSM compared to matching pre capillary

Question 2

What is the purpose of vasoconstriction in exercise? Is there
venoconstriction?

Which NS controls this and where is it

Answer 2

• Sympathetic adrenergic nerves supply all vascular beds, distribution in pre and post capillary causing Vasoconstriction.

During exercise
- Arterial constriction helps to reduce blood flow through organ beds in GI tract to shunt more blood to muscle and skin (constriction offset by other means of dilation)

• Venous constriction helps to increase flow to increase venous return to the heart
• -> increasing SV to match increase in HR to get overall increase in CO.

Question 3

What happens if you don’t increase venous return, only HR

Answer 3

The CO stays the same because the time for heart filling gets reduced so stroke volume decreases proportionally

Question 4

What is the effect of increased precapillary resistance on the extrusion/ recovery of fluid from the capillaries

Answer 4

1. Increased precapillary resistance
   - -> reduced post resistance flow
   - -> quicker drop in mean capillary hydrostatic pressure so that it goes below the mean pressure of interstitial fluid
   - -> Favours faster recovery of fluid back to capillary (collection of waste)

decreased resistance = more extrusion of fluids into tissues

Question 5

List the 5 methods of local control of blood flow in bv at tissues

Answer 5

Autoregulation, Reactive hyperaemia (increase in blood), Myogenic hypothesis, Metabolic hypothesis,
Vascular endothelium hypothesis

Question 6

What is Autoregulation

Answer 6

Innate ability of vessels to adapt to changes in perfusion pressure in order to maintain a normal blood flow

eg.
- If perfusion increases==> flow increases

• triggers vasocontriction,
• Resistance increases to reduce flow even though perfusion pressure is still high.

Question 7

What is reactive hyperaemia

Answer 7

1. Blood vessel occlusion for a short period is released
2. Causes blood flow to rise above pre-occlusion level (hyperemia)
3. This is maintained for period roughly proportional to duration of occlusion

Question 8

What is Myogenic hypothesis

Answer 8

1. Increased perfusion increases vascular pressure throughout circulation
2. Increased transmural pressure leads to vascular distension
3. Stretch elicits SM contraction

Question 9

What is Metabolic hypothesis, where does it occur

• not related to full circuit vasodilation

Answer 9

During exercise.

Vasodilation in bv in skeletal/cardiac muscle (precapillary vessels)

=> increase blood flow = nutrients to these tissues because of build up metabolites (from cardiac/skeletal muscle cells) in interstitial space which act on VSM.

Vasodilation triggers

• ATP by product adenosine
• inorganic phosphate from ATP use
• Changes in osmolarity in the interstitial space
• increased K+ extrusion from skeletal/cardiac cells due to high Na/K/ATPase.

Question 10

What is the vascular endothelium hypothesis

Answer 10

1. Increased blood flow increases shear stress on endothelium
2. Leads to release of NO
3. NO causes relaxation of VSM