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fluid pumped by the heart that circulates throughout the body via the arteries, veins, and capillaries (see circulatory system; heart). An adult male of average size normally has about 6 quarts (5.6 liters) of blood.
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The liquid portion that remains when blood is allowed to clot spontaneously and is then centrifuged to remove the blood cells and clotting elements. It has approximately the same volume (55%) as plasma and differs from it only by the absence of fibrinogen. See Fibrinogen
Blood serum contains 6–8% solids, including macromolecules such as albumin, antibodies and other globulins, and enzymes; peptide and lipid-based hormones; and cytokines; as well as certain nutritive organic materials in small amounts, such as amino acids, glucose, and fats. Somewhat less than 1% of the serum consists of inorganic substances. Small amounts of respiratory gases are dissolved in the serum, as is the gas nitric oxide, which serves as a chemical messenger and vasodilator. Small amounts of waste material are also present. These substances, along with other small molecules which are not bound to blood proteins, are filtered out as blood flows through the kidney. See Blood, Kidney
Certain types of sera, both human and animals, are used in clinical medicine. Immune serum and hyperimmune serum either are developed by naturally occurring disease or are deliberately prepared by repeated injection of antigens to increase antibody titer for either diagnostic tests or the treatment of active disease. These sera are referred to as antisera, since they have a specific antagonistic action against specific antigens. See Antibody, Antigen, Biologicals, Immunity
By custom, the clear portion of any liquid material of animal origin separated from its solid or cellular elements is also referred to as sera. These fluids are more properly referred to as effusions. See Serology