Red Blood Cells

Red blood cells, or erythrocytes, as a part of Blood group are tiny, round, biconcave disks averaging7.5 microns (0.003 in) in diameter. A normal 76.5 kg (170-lb) main has about 5 l (5.3 qt) of blood, containing more than 25 trillion red cells. Because the normal life span of red cells is only about 120 days, more than 200 billion cells are normally destroyed each day by the spleen and must be replaced. Red cells are made in the bone marrow.

The main function of the red blood cells is to transport oxygen from the lungs to the tissue. Oxidations of various food substances to supply most of the energy requirements of the body results in carbon dioxide, one of the chief waste products, and red blood cells carry it to the lungs for release and to pick up more oxygen.

The substance in the red blood cells that is largely responsible for their ability to carry oxygen and carbon dioxide is hemoglobin, the material that gives the cells their red color. Produced in the bone marrow and broken down in the spleen, it is a protein complex comprising many linked amino acids, and occupies almost the entire volume of a red blood cell. Essential to its structure and function is iron.

Blood is a tissue comprising two main components; a plasma fluid (A) and freely moving blood cells, which are white (B) or red (C). Plasma, comprising 90% water, does not have cells but contains proteins and salts that buffer substances traveling through the blood vessels. White blood cells include three types of granulocytes, which are basophils (1), eosinophils (2), and neutrophils (3); small ad large lymphocytes (4, 5) and monocytes (6). White blood cells defend the body against infection by engulfing the invading bacteria and by healing wounds. Platelets (7) are cell fragments that catalyze blood cloting. Red blood cells (8), which have no nuclei, are shaped like indented disks. These cells contain hemoglobin, protein that transports oxygen to body tissues.