Question

for a blood volume of 5L and a cardiac output of 5L/ minute, what is the circulation time, that is to say, the average time required for a blood cell to pass completely around the systemic and pulmonary circuits?

a. same question above for a shrew?

b. what about an exercising shrew?

Answer 1

For the blood volume of 5L and a cardiac output of 5L/minute, flow through systemic and pulmonary circuits as-

Approximately 5L of blood are pumped from the left ventricle each minute in an adult human. If the corresponding volume was not pumped by the right ventricle every minute then the left heart would have inadequate return to maintain the 5L output per minute.

If left ventricular output decreases rapidly while that of the right ventricle remains stable, pulmonary blood volume (and therefore pulmonary pressure) rises until the output of the two ventricles make equal. The pulmonary circulation all the time contains less blood than the systemic circulation.

In an around 5L blood volume with the heart containing 360mL in diastole (filled, just preceding to contraction) the pulmonary circulation hold only 440mL compare to 4200mL in the systemic circulation. It may help to appreciate when you realise that the complete right cardiac output goes to the pulmonary circulation while left ventricular output must be divided up among the systemic organs: brain; muscle; viscera; etc. This ample allotment contains a set more blood volume at any one time than the pulmonary circuit but the volume incoming and leaving are the same.