Coordinated CV responses 1

Question 1

Why does cardiac output decrease when you stand up?

Answer 1

There is increased hydrostatic pressure in the feet so fluid moves from the capillaries into the interstitium. The loss of fluid reduced the blood volume and so decreases cardiac output.

Question 2

How is fluid loss in the capillaries of the feet during orthostasis reduced?

Answer 2

Pressure is reduced in the capillaries of the feet by the constriction of arterioles, reducing the pressure of the blood entering capillaries.
This is done by reflex vasoconstriction via baroreceptors. Also a distension of veins causes a veno-articular axon reflex which causes constriction via sympathetic action/

Question 3

What is the veno-articular axon reflex?

Answer 3

Sympathetic action, baroreceptors in veins causing the constriction of artierioles reducing the pressure of the blood.

Question 4

How do varicose veins form?

Answer 4

When tributary veins fill up and the valve fails then they swell.

Question 5

How do the veins in the cerebrum stay open even though they have subatmospheric pressure?

Answer 5

There cerebral spinal fluid also exerts a (greater) negative pressure, holding the veins open.

Question 6

What is vasovagal syncope?

Answer 6

Faint where there is vasodilation and vagally mediated bradycardia.
When you stand for too long, blood pools at the feet so there is oedema into the feet reducing the blood vol and therefore blood pressure. To compensate there is an increase in TPR and HR. Increased HR (vagally mediated bradycardia) and drop in BP (reduced cerebral blood flow) leads to faint.