Question

1. What does vasoconstriction or vasodilation do to venous return and cardiac output? How does this occur?

2. How would viscosity change as the number of red blood cells increase or decrease?

3. Give an example of when the size of a blood vessel's lumen would change.

4. Would vasoconstriction or vasodilation make the lumen smaller? What happens to the resistance when the lumen gets smaller? What happens to blood pressure?

Answer 1

1. ANSWER: Vasoconstriction increases the pressure on the veins as it does in an artery. But, vasoconstriction in arteries would decrease the blood flow whereas vasoconstriction in veins would increase the flow hence the venous return to the heart also increases. In vasodilation, the venous return would decrease as the pressure on the veins decreases.

2. ANSWER: Increased red blood cells would increase the hemotocrit hence the viscosity of the blood would increase. Blood viscosity depends on the hematocrit. Decreased blood cells would also slightly decrease the viscosity of the blood.

3. ANSWER: Decrease blood vessel size would be due to temperature decrease, increased Po2, angiotensin, vasopressin, thromboxane A2.

Blood vessel increase is due to temperature increase, decreased Po2, PGI2, bradykinin.

4. ANSWER: Vasoconstriction would make the lumen smaller and vasodilation make the lumen bigger. Vasoconstriction would increase the pressure on the walls and thus Increases the blood pressure.