Main Types of Blood Cells

Known for their bright red color, red blood cells (RBCs) are the most abundant cell in the blood, accounting for about 40-45 percent of its volume (and its color via the hemoglobin, a protein that helps carry oxygen from the lungs to the rest of the body). The shape of a red blood cell is a biconcave disk with a flattened center—in other words, both faces of the disc have shallow bowl-like indentations, giving it a donut-like appearance.

Production of red blood cells is controlled by erythropoietin, a hormone produced primarily by the kidneys. Red blood cells start as immature cells in the bone marrow, and after approximately seven days of maturation, are released into the bloodstream. Unlike many other cells, red blood cells have no nucleus and can easily change shape, helping them fit through the various blood vessels in your body. However, while the lack of a nucleus makes a red blood cell more flexible, it also limits the life of the cell as it travels through the smallest blood vessels, damaging the cell’s membranes and depleting its energy supplies. The red blood cell survives on average only 120 days.

The percentage of whole blood volume that is made up of red blood cells is called the hematocrit and is a common measure of red blood cell levels.

White blood cells (WBCs) protect the body from infection. They only account for about 1 percent of your blood.

The most common type of white blood cell is the neutrophil, which is the “immediate response” cell and accounts for 55-70 percent of the total white blood cell count. Each neutrophil lives less than a day, so your bone marrow must constantly make new neutrophils to maintain protection against infection.

Transfusion of neutrophils is generally not effective since they do not remain in the body for very long.

The other major type of white blood cell is a lymphocyte, of which there are two types. T lymphocytes help regulate the function of other immune cells and directly attack various infected cells and tumors. B lymphocytes make antibodies, which are proteins that specifically target bacteria, viruses and other foreign materials.

Platelets are not actually cells but rather small fragments of cells. Platelets help the blood-clotting process (or coagulation) by gathering at the site of an injury, sticking to the lining of the injured blood vessel and forming a platform on which blood coagulation can occur. This results in the formation of a fibrin clot, which covers the wound and prevents blood from leaking out. Fibrin also forms the initial scaffolding upon which new tissue forms, thus promoting healing.

A higher-than-normal number of platelets can cause unnecessary clotting, which can lead to strokes and heart attacks; however, thanks to advances made in antiplatelet therapies, there are treatments available to help prevent these potentially fatal events. Conversely, lower-than-normal counts can lead to extensive bleeding.

Plasma, a mixture of water, sugar, fat, protein and salts, is the liquid component of blood. Plasma’s primary job is to transport blood cells throughout your body along with nutrients, waste products, antibodies, clotting proteins, chemical messengers such as hormones and proteins that help maintain the body’s fluid balance.