Blood distribution mechanism

Question 1

What is the vascular shunt mechanism?

Answer 1

During exercise, the cardiovascular system redistributes the blood so that more of it goes to the working muscles and less of it goes to other body organs

Question 2

What percentage of the blood in redistributed to the muscles during exercise?

Answer 2

• 87% at exercise

- 20% at rest

Question 3

What is vasodilation? And how does it happen?

Answer 3

• Blood vessels open up or increase in volume to allow greater blood flow.
• When recognising an increase in acidity levels and decrease in oxygen within the blood, vessels dilate to promote greater blood flow.

Question 4

Why does venous return need to happen?

Answer 4

During exercise the blood pressure in the veins is not high enough to increase the level of venous return and so maintain the higher stroke volume and cardiac output which exercise requires.

Question 5

How much blood does venous return need to return to the heart?

Answer 5

Venous return must constitute three fifths of the blood circulating the body at any time in order to maintain a steady blood flow.

Question 6

What are pocket valves?

Answer 6

Located within the veins to prevent the back flow of blood and help it towards the heart

Question 7

What are muscle pumps?

Answer 7

Many veins are situated between skeletal muscles, which when they contract and relax, squeeze on the veins and help push the blood back towards the heart.

Question 8

What is smooth muscle?

Answer 8

The wall of each vein contains smooth muscle which contracts to help push the blood back towards the heart

Question 9

What is the respiratory pump?

Answer 9

The respiratory pump helps return blood in the thoracic cavity and abdomen back to the heart. Whilst exercising we breathe faster and deeper which rapidly changes the pressure within the thorax between high and low to help to squeeze the blood in the area back to the heart.

Question 10

How does gravity aid venous return?

Answer 10

Veins in the upper body are aided by gravity in order to return blood to the heart.

Question 11

What is the effect of restricted venous return?

Answer 11

When venous return is restricted, the left ventricle receives less oxygenated blood, resulting in a low-end diastolic volume. When EDV is low, the ventricle fails to stretch, an important precursor to a forceful contraction and ejection of blood. Low EDV can limit the heart’s capacity to meet the oxygen demands of the body.

Question 12

What can restricted venous return do?

Answer 12

• Lower cardiac output
• Reduced blood pressure
• Reduced flow rate.
  = REDUCED PERFORMANCE