AP BIOLOGY

ANIMAL PHYSIOLOGY

HUMAN CIRCULATION

Question [CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
Valves in veins serve to:
A
Release excessive pressure to protect these thin-walled vessels.
B
Counteract the crushing force of surrounding skeletal muscles.
C
Prevent backflow of blood in the absence of high blood pressure.
D
Adjust blood pressure by compartmentalizing the venae cavae.
Explanation: 

Detailed explanation-1: -They are larger and hold more blood than the arteries. The blood passing through the veins is deoxygenated (except in pulmonary veins ) and flows at a low pressure. It flows slow and steady against the direction of gravity. Therefore, veins have valves to prevent the backflow of blood.

Detailed explanation-2: -Final answer:The valve which prevents back flow of blood in the veins is Semilunar valve.

Detailed explanation-3: -Blood flows under low pressure in veins. Hence, veins have valves to prevent the backflow of blood and make sure the blood keeps moving regularly.

Detailed explanation-4: -If gravity or muscle contractions try to pull the blood backward or if blood begins to back up in a vein, the flaps are pushed closed, so the blood does not flow backward. Thus, valves help the return of blood to the heart-by opening when the blood flows toward the heart and closing when blood might flow backward.

There is 1 question to complete.