心脏是如何工作的
We talked last week about the life of famed heart doctor Michael DeBakey. He died this month at age ninety-nine.Today, we talk about the object of his work. The heart is a complex organ that starts beating a few weeks after conception. At this point the heart is a tube. In the coming days, it grows and bends into the shape of the heart.
Later, it divides into four parts. As the heart beats, it pumps blood through these chambers and the blood vessels in the body. The body is estimated to have at least ninety-six thousand kilometers of blood vessels.
That is about the same as two and a half times around the Earth. But blood goes the distance in about twenty seconds on its way back to the heart. Each day the heart pumps about eight thousand liters of blood.
The blood feeds the brain and other organs with oxygen and nutrients. It also carries away carbon dioxide and other waste.The heart pumps by expanding and contracting of muscle. In a healthy adult, the heart beats an average of seventy-two times a minute -- about one hundred thousand times a day.
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