Human blood

Human blood is a specialized bodily fluid that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells.

Composition

Blood is composed of plasma and cells. The cells are mainly erythrocytes, leukocytes, and thrombocytes.

Plasma

Plasma is the liquid component of blood, in which the blood cells are suspended. It makes up about 55% of the body's total blood volume. Plasma is mostly water (90% by volume) and contains dissolved proteins, glucose, clotting factors, electrolytes, hormones, carbon dioxide, and oxygen.

Red Blood Cells

Erythrocytes are the most common type of blood cell and the principal means of delivering oxygen to the body tissues via the blood flow through the circulatory system. They take up oxygen in the lungs or gills and release it while squeezing through the body's capillaries.

White Blood Cells

Leukocytes are the cells of the immune system that are involved in protecting the body against both infectious disease and foreign invaders. Five different and diverse types of leukocytes exist, and they are all produced and derived from a multipotent cell in the bone marrow known as a hematopoietic stem cell.

Platelets

Thrombocytes are a component of blood whose function (along with the coagulation factors) is to stop bleeding by clumping and clotting blood vessel injuries.

Functions

Blood performs many important functions within the body, including:

• Supplying oxygen to tissues (bound to hemoglobin which is carried in red cells)
• Supplying nutrients such as glucose, amino acids, and fatty acids (dissolved in the blood or bound to plasma proteins)
• Removing waste such as carbon dioxide, urea, and lactic acid
• Immunological functions, including circulation of white blood cells, and detection of foreign material by antibodies
• Coagulation, which is one part of the body's self-repair mechanism
• Messenger functions, including the transport of hormones and the signaling of tissue damage
• Regulation of body pH
• Regulation of core body temperature

Blood Types

Human blood is classified into different blood groups based on the presence or absence of certain antigens on the surface of red blood cells. The most well-known and clinically significant blood group systems are the ABO and the Rh systems.

Blood Disorders

There are many disorders of the blood, including:

• Anemia
• Leukemia
• Hemophilia
• Thrombocytopenia

See Also

• Hematology
• Blood transfusion
• Blood donation

External Links

• Blood - WikiMD