Blood is a fluid in your body that contains red and white blood cells, platelets and plasma. The most important job of blood is to carry oxygen to your body’s tissues. This fluid also removes waste products from the tissues. In addition to oxygen, it also carries antibodies and nutrients to the tissues.
Photo: Platelets (gray) and red and white blood cells (Creative Commons: Wellcome Images).
Composition of Blood
Blood is primarily plasma which is a liquid. Plasma is mostly water but contains small amounts of proteins, sugars, minerals, and hormones. Carbon dioxide dissolves in the plasma and is transported away from the body’s tissues. Plasma makes up about 55% of the blood.
Within the plasma, there are red blood cells (erythrocites), white blood cells (leucocytes) and platelets. Red blood cells obtain their color from the chemical hemoglobin which is a protein. Hemoglobin binds and unbinds itself to oxygen and is the primary means of transporting oxygen to the body’s tissues. These cells are produced in the bone marrow. When they grow older (after 3-4 months) they are broken down in the spleen, liver and lymph nodes.
White blood cells helps protect the body from infectious diseases and foreign invaders. They make up about 1% of the blood. There are five main types of these defensive cells. These cells attack bacteria, fungi, parasites, and virus or tumor infected cells. They may also help regulate inflammatory responses by releasing histamines.
Where there is an injury, platelets help control bleeding by clumping and clogging blood vessels.
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Heart Health Center, WebMD.