Human Blood Volume

Many people wonder how much blood their body contains. This can be readily worked out. It varies with weight. The total blood volume (as this is called) is between 60 and 80 ml for each kilogram of weight. (A kilogram equals 2.2 pounds.) So you can easily calculate the amount of blood in your body.

Of this total, in men, between 26 and 33 ml/kg is made up of red-cell volume, and 22 and 29 ml/kg in women. Plasma (the fluid part of the blood) equals 40 – 50 ml/kg.

All these figures may be mind-boggling to the reader, but to the doctor they are all of considerable significance. They may denote the difference between good health and poor health. What is more, when a person with a “low blood count” or “low hemoglobin” is given treatment, subsequent blood tests will accurately indicate the response that has occurred. This is even more important.

A person with a low red-cell count and low hemoglobin is said to be anemic. The white cells (leucocytes) represent the defense mechanism of the body. Instead of one type of cell as with the red series, there are a variety of white ones.

There are many sub-classifications, but only the main types will be mentioned. The chief ones are the neutrophils and lymphocytes. The others are called monocytes, eosinophils and basophils.

Basically, the neutrophils are concerned with destroying invading germs. They simply approach a germ, roll over it and the germ becomes part of the cell and is destroyed. This is called phagocytosis, and is a case of the big fish swallowing the little fish. This can actually be seen under the microscope. Normally in the adult, between 40 and75 per cent of the white cells are of this kind.

Between 20 and 45 per cent are lymphocytes. These are formed in the lymph glands and lymph tissue of the body, and they are responsible for producing special chemicals called antibodies. This gives the body special immunity against invading toxins. It forms the basis of the protective immunization injections that babies are given soon after birth. It is part of a very effective immunological system.