Lecture 10: Venous blood flow and the heart

Question 1

How does compliance differ btw arteries and veins?

- VEINS

Answer 1

Veins –> thin wall –> complaint - expand & stretch

• veins can expand significantly with little changes in pressure = compliant
• veins are able to store more blood at lower pressure due to their thin was, which increases their compliance - can increase their volume capacity

Question 2

How does compliance differ btw arteries and veins?

- ARTERIES

Answer 2

arteries —> thick muscular wall –> rigid & stiff

• can only undergo small changes in diameter
• as pressure increases arteries under very little change in diameter therefore can’t increase their volume capacity

veins are thin-walled vessels that have high compliance compared with arteries

Question 3

What does the high compliance of veins allow?

Answer 3

Allows a lot of blood to be stored - has survival value when there is decrease in arterial pressure - stored blood in veins is uses as a blood reserve
- however high vascular compliance means that blood tends to accumulate ‘pool’ in veins

Question 4

High vascular compliance in veins means that blood tends to assumable ‘pool’ in veins. How is this venous pooling counteracted?

Answer 4

1. Venous valves

2. Tone of the surrounding tissue

Question 5

How to venous valves counteract venous pooling in veins?

Answer 5

• Valves segment blood and make the vein a discontinuous column so that pressure of segment of blood is working against the valves rather then the segment of blood below it.

Question 6

How does tone of surrounding tissue counteract venous pooling in veins?

Answer 6

• muscle tone acts to stiffen veins —> making them less compliant and less prone to pooling
• skeletal muscle can alter its tensile state

Question 7

How do veins have ‘survival value’

Answer 7

During a life threatening situation, mean arterial blood pressure drops - veins then undergo vasoconstriction(smooth muscles constrict) which causes stored blood in veins to be pumped from the venous circuit to the arterial system

Question 8

What effect foes venous return to the heart have?

Answer 8

• muscle contraction increase venous flow
• –> when muscle constrict, it exerts pressure on the veins which squeezes the blood in both directions but due to valves it will flow toward the heart
• increased venous return = increased stroke volume
• –> venous return directly affects the SV and performance of the heart