How long does it take your heart to circulate the total amount of blood in your body?
(Lansing State Journal, December 01,1993)

For a person at rest, it takes just about one minute.  If you are more active, it will take less time. Exactly how long depends on several things: the rate at which your heart beats, how big your heart is, and, to a certain extent, how big you are as well.

A person's heart beats about 65 to 75 times a minutes.  This is called  the beat rate.  With each beat, the heart pumps about 60 to 70 milliliters of blood.  If you multiply the two values together, you find that the cardiovascular output is just about four to five liters per minute.  Can you guess how much blood an individual has?

If you exercise, your heart rate increases, and it decreases when you rest.  Your body has a remarkable way of knowing just how much blood should be flowing to properly distribute the nutrients it needs.  The primary means of controlling cardiovascular output is by controlling the beat rate with hormones.  One, called acetylcholine , acts to decrease beat rate, when you are resting or sleeping.  Another, called norepinephrine, increases the rate at which your heart beats, when you are active or excited.  The balance of these two hormones helps to keep the rate of your blood flow just right.

[ Back to Ask Science Theatre | Back to Ask Science Theatre Date Index ]
Back to MSU Science Theatre Home Page