Structure and Function of the Cardiovascular System

Structure and Function of the Cardiovascular System

Bertha is 81 years old, and was admitted to the hospital after contracting community-acquired pneumonia. She had been bedridden for 3 days, so her nurse arranged for a physiotherapist to assist her out of bed to help her slowly regain her mobility. Bertha decided not to wait for the physiotherapist, and after arising in the morning, she eased herself out of the bed and stood up. Suddenly, Bertha’s vision dimmed, and she felt light-headed and dizzy. A passing nurse saw her fall back to the bed and rushed to help her. The nurse comforted Bertha, and then suspecting orthostatic hypotension, went to find a sphygmomanometer to check her blood pressure.

1. Prolonged bed rest decreases plasma levels and vasomotor tone, which can both lead to orthostatic hypotension. How do changes in vascular resistance and radius affect blood flow? Assuming Bertha is otherwise healthy, how does her heart activity change to compensate for the orthostatic hypotension she experienced?

2. Considering the venous circulation, how is blood from the lower extremities returned to the heart?

3. Why did Bertha’s capillary fluid pressure (or hydrostatic pressure) change when she moved from a lying to standing position?