Red Blood Cells

Most of the cells in the blood are red blood cells. These are highly specialized cells that have been stripped of everything, including the nucleus. They are biconcave disk-shaped that contain hemoglobin, The red blood cells supply oxygen to all body cells and remove the carbon dioxide wastes that result from metabolism.

A typical erythrocyte contains about 270 million hemoglobin molecules, with each carrying four heme groups.

The red blood cells store collectively about 3.5 grams of iron, more than five times the iron stored by all the other tissues combined.

Women have about 4 million to 5 million erythrocytes per cubic millimeter of blood.

Men about 5 million to 6 million (people living at high altitudes with low oxygen tension will have more RBCs).

Life Cycle

The process by which red blood cells are produced is called erythropoiesis. Erythrocytes are continuously being produced in the red bone marrow of large bones, at a rate of about 2 million per second. (In the embryo, the liver is the main site of red blood cell production).

RBCs develop form stem cells to mature erythrocytes in about 7 days and live a total of about 120 days. The aging cells are engulfed by phagocytes, destroyed and their materials are released into the blood. The main sites of destruction are the liver and the spleen. The heme constituent of hemoglobin is eventually excreted as bilirubin.

What Is Hemoglobin?

Hemoglobin is the protein molecule in red blood cells which carries oxygen from the lungs to the body's tissues and returns carbon dioxide from the tissues to the lungs. The iron contained in hemoglobin is responsible for the red color of blood.

The hemoglobin molecule is composed of four separate polypeptide chains of amino acids, two alpha chains and two beta chains as well as four iron-bearing heme groups that bind oxygen. The alpha chains are coded for genes on chromosome 16; the beta chains by a gene on chromosome 11. Mutations and deletions in these genes cause one of the many hemoglobinopathies.

What Are Normal Hemoglobin Values?

The hemoglobin level is expressed as the amount of hemoglobin in grams (gm) per deciliter (dl-100ml) of whole blood.

The normal ranges for hemoglobin depend on the age, beginning in adolescence, and the sex of the person.

- Newborns: 17-22 gm/dl
- One week of age: 15-20 gm/dl
- One month of age: 11-15 gm/dl
- Children: 11-13 gm/dl
- Adult men: 14-18 gm/dl
- Adult women: 12-16 gm/dl
- Men after middle age: 12.4-14.9 gm/dl
- Women after middle age: 11.7-13.8 gm/dl

A low hemoglobin is referred to as being anemic. There are many reasons for anemia. Some of the more common reasons are loss of blood, nutritional deficiency (iron, vitamin B12, folic acid), bone marrow problems (replacement of bone marrow by cancer, suppression by chemotherapy drugs), and abnormal hemoglobin (sickle cell anemia).

Heme (Coenzyme)

A non protein organic substance that usually contains a vitamin or mineral and combines with a specific protein, the apoenzyme, to form an active enzyme system (Hb). Heme is an organic molecule derived from porphyrin with an iron atom at the center.

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