Blood Products

Red blood cells (also called erythrocytes) carry oxygen from the lungs to all the cells in the body and take carbon dioxide back to the lungs to be exhaled. The red blood cells represent the most volume, making up 40-45 percent of one’s blood. They are shaped like tiny doughnuts, with an indentation in the center instead of a hole. They contain a special molecule called hemoglobin, which contains four iron atoms, and each iron atom can bind with one molecule of oxygen, allowing each hemoglobin molecule to carry four molecules of oxygen. In the capillaries, where there is little oxygen, the hemoglobin readily sheds the oxygen it is carrying and allows it to be absorbed by the body’s cells. The iron in hemoglobin is what makes blood red.

White blood cells (leukocytes) help the body fight infections and diseases. White blood cells “digest” harmful viruses and bacteria, such as those entering the body through a cut or a scrape, or developed in an ear infection or the flu. There are three types of white blood cell: granulocytes, lymphocytes, and monocytes. Granulocytes contain granules, which hold digestive enzymes and can kill invading bacteria and parasites. Lymphocytes help coordinate the body’s immune system. They produce antibodies — the immune proteins, which help remove foreign substances and invading organisms — and invade cells in the body that are infected with viruses. Monocytes, the largest kind of white blood cells, enter the tissues of the body and turn into even larger cells called macrophages. These eat foreign bacteria and destroy damaged, old, and dead cells of the body itself. This scavenging function clears the way for tissue healing and repair.

Platelets (thrombocytes) help blood to clot. They are tiny, colorless, irregularly shaped, cell fragments from large bone marrow cells. In their “resting” state, platelets look like two plates stuck together (hence the name). When they are “activated” to help form a clot, they change shape and look like tiny round blobs with tentacles. When bleeding occurs, platelets clump together and release a substance, which starts a chain of chemical events, called “coagulation cascade.” It produces long protein threads, which help create fibrin, which in turn helps form the clot over the wound.

Plasma Plasma is a clear, straw-colored liquid that carries the blood cells and various hormones, minerals, nutrients, and other materials through the body. It makes up a little more than half of the total blood volume. Plasma is about 90 percent water. The remaining ten percent are made up of over 200 known substances, including proteins, clotting agents, hormones, vitamins, cholesterol, sugar (glucose), electrolytes like sodium, potassium, and calcium, as well as other materials the body needs.

Learn about the role of each blood component in modern medicine.