Most people are aware that the heart is a muscular organ that acts as a pump, pushing the blood around to all the tissues, supplying nutrients and oxygen so that we can function. But how many are aware that we have another pump that helps blood circulate? It is called the muscle pump and it plays an important role returning blood back to the heart.
Factors Used in Getting Blood Back to the Heart
The heart works by squeezing, then relaxing. When it relaxes, it fills up, getting ready and primed for the next squeeze. However, when it relaxes the forward force of blood flow stops and the force of gravity tries to take over. Since man is an upright animal, a problem presents itself when blood in the lower extremities tries to return to the heart against the force of gravity. The farther down the leg the blood is located, the greater the force of gravity, and the more difficult it is for blood to return to the heart.
When you think about it, there are only about 4 things that are present to help this blood return to the heart. The first is any residual forward energy left over from the force of heart contraction. The second is the fact that there are a series of one-way valves in the veins of the lower extremities. These valves are present down to a vessel size of 40 micrometers—that is very small. These valves close during cardiac relaxation, preventing blood in the lower extremities from flowing backward under the influence of gravity.
The third factor concerns a negative pressure gradient that is set up in the chest as the diaphragm descends and the chest wall expands. When the empty heart relaxes after contraction, another negative pressure gradient is set up. The net effect is to move blood toward and into the heart along this gradient.
The muscle pump is the fourth factor. It helps us fight gravity. If gravity starts winning the fight, the legs begin to hurt and swell. The blood in the area begins to move very slowly and patients become susceptible to blood clots. The muscle pump can help prevent the blood from becoming stagnant and can help return blood to the heart. Its action can prevent blood clots.
The Muscle Pump in Action
Here’s how the muscle pump works:
Most of the blood from the lower extremity returns to the heart via the deep veins (see above). The deep veins are surrounded by muscle as depicted above. When you run, walk, climb stairs, or just squeeze your calf muscle, here is what happens:
The muscles contract, squeezing the thin walled veins, sometimes to the point of nearly emptying them out. And the blood? It gets ejected upwards toward the heart. This is the only way it can go as long as the one-way valves are intact. So with every contraction of the lower extremity muscles the blood is pumped along heading back to the heart. So it is the lower extremity muscles that act as a circulatory assistant.
Mobility is Important in Keeping Your Blood Flowing
We can now see why it makes sense to get up and walk around during a long trip and to flex our calf muscles periodically. This will push the blood toward the heart, prevent swelling, prevent stagnation of the blood and blood clot formation. On long trips we should let the muscle pump do its job!
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