Mathematics and Biology

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Math Awareness Month 1999

The Heart

the circulatory system consists of two distinct circuits which allow for oxygen transport to body cells, and CO2 removal via the lungs

This figure demonstrates the heart and the two cycles of blood through the body. The cycle through the lungs, where blood is enriched with oxygen, is known as the pulmonary cycle; the cycle through the body, where blood supplies all the cells with oxygen and picks up carbon dioxide, is called the systemic cycle. It is crucial for the heart to keep the two cycles separate, so heart is divided into the right and the left halves, which have no direct connections whatsoever. The right half is responsible for the pulmonary cycle and the the left - for the systemic. The two halves are each divided into two chambers: the ventricle and the atrium. Blood comes into the heart through the atria and leaves through the ventricles.

The heart pumps blood by contracting and relaxing the muscles which line the heart walls, squeezing blood out and then letting new blood in. This cycle repeats itself again and again; in the course of a human life the heart muscle contracts about two billion times! Such repetitious behavior is known as periodic, and mathematicians have devised special functions to describe it (see page 8).

When the heart contracts, it exerts pressure on the blood which is in it, forcing it to move out. This wave of blood pushes through the body, going from high pressure on the left ventricle to low pressure in the right atrium (in the case of systemic flow). This difference in pressure is what drives the blood flow through the body. The exact equation which describes this relationship is on page 4.

One very important parameter to consider is the heart rate, which is the number of times it contracts in a minute. During exercise, heart rate may increase by over a factor of 2, compared with the resting rate. Heart rate also determines the rate of blood flow, which is discussed in page 6.

M & B Exhibits | intro | pg 2 | pg 3 | pg 4 | pg 5 | pg 6 | pg 7 | pg 8