7: Circulatory System

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All the blood in the body is under the control of the heart ....
The blood current flows continuously in a circle and never stops.

As translated from Neiching, a Chinese treatise on internal diseases written on strips of bamboo in about 2600 B.C.

The circulatory system includes the heart, blood vessels, and blood. The heart pumps blood through an elaborate system of blood vessels (Figure 7.1), continuously delivering oxygen and nutrients to the tissues, carbon dioxide to the lungs to be exhaled, and waste products to the kidneys. The circulatory system also transports other key substances such as hormones and antibodies and plays a central role in regulating body heat by “transporting” heat from one part of the body to another.

Because blood carries substances to and from cells, it’s often sampled and analyzed. Think of trucks (blood) that constantly transport material to and from buildings (body tissues). If you can’t look inside a building, you can get a good idea of what’s happening there by pulling aside a truck (taking a blood sample) to see what it’s carrying. To extend the analogy, trucks (blood) must have an efficient and well-maintained transportation system (heart and blood vessels) to do a good job.

7.1: Heart
7.2: Blood Vessels, Blood Pressure
7.3: Blood
Blood is made up of red blood cells, white blood cells, and platelets suspended in a fluid called plasma. Blood is about one-half cells and one-half plasma. Blood continually mixes as it moves through the heart and blood vessels. If a blood sample is put in a tube with an anticoagulant (a substance that prevents clotting), the red blood cells settle to form the bottom half of the blood sample. On top of the red blood cell layer is a thin layer of white blood cells.
7.4: White Blood Cells
White blood cells play a key role in immunity by destroying bacteria and other foreign substances. They defend the body against infections and tumors. Leukemia and AIDS involve white blood cells. We see, again, the familiar theme of too much or too little as a problem. In leukemia, there’s an uncontrolled production of white blood cells. The overwhelming abundance of white blood cells, causes a potentially fatal disruption of normal body processes.
7.5: Summary