blood
(blŭd 
)
The fluid that contains cells; circulates through the heart, arteries, veins, and capillaries; carries nourishment, electrolytes, hormones, vitamins, antibodies, heat, and oxygen to the tissues; and takes away waste matter and carbon dioxide.
SEE: erythropoietin.
Characteristics: Blood has a distinctive, somewhat metallic, odor. Arterial blood is bright red or scarlet and usually pulsates if the artery has been cut. Venous blood is dark red or crimson and flows steadily from a cut vein.
Composition: Human blood is about 52% to 62% plasma and 38% to 48% cells. The plasma is mostly water, ions, proteins, hormones, and lipids. The cellular components are the erythrocytes (red blood cells [RBCs]), leukocytes (white blood cells [WBCs]), and thrombocytes (platelets). The leukocytes comprise neutrophils, eosinophils, basophils, lymphocytes, and monocytes.
SEE: illus. ; illus. TYPES OF BLOOD CELLS
Cell types found in smears of peripheral blood from normal individuals.
; buffy coat; plasma; serum.An adult weighing 70 kg has a blood volume of about 5 L or 70 mL/kg of body weight. Blood constitutes about 7% to 8% of the body weight. The pH of the blood is from 7.35 to 7.45. The specific gravity of blood varies from 1.048 to 1.066, the cells being heavier and plasma lighter than this. Blood is of slightly higher specific gravity in men than in women. Specific gravity is higher after exercise and at night.
SEE: blood count; cell; erythrocyte; leukocyte; plasma; platelet.
Function: In passing through the lungs, the blood gives up carbon dioxide and absorbs oxygen; after leaving the heart, it is carried to the tissues as arterial blood and then returned to the heart in the venous system. It moves in the aorta at an average speed of 30 cm/sec, and it makes the circuit of the vascular system in about 60 seconds. RBCs carry oxygen; WBCs participate in the immune response to infection; platelets are important in blood clotting. The plasma transports nutrients, waste products, hormones, carbon dioxide, and other substances, and contributes to fluid-electrolyte balance and thermal regulation.
Formation: RBCs are produced in the red bone marrow at the rate of about 2,400,000/sec, and each RBC lives for about 120 days. In healthy individuals, the concentration of RBCs in the blood remains stable over time. Platelets and WBCs are also produced in the red bone marrow, and agranular WBCs are produced in lymphatic tissue.
arterialized b.Oxygenated blood
cord b.The blood present in the umbilical vessels connecting the placenta to the fetus. Because cord blood is immunologically immature, it is esp. useful in transfusion therapy and hematological transplantation.
defibrinated b.Whole blood from which fibrin has been removed. It does not clot.
fresh b.Blood that has been collected less than 48 hours prior to its use in a transfusion.
SEE: occult blood.
oxygenated b.Blood that has been exposed to oxygen in the lung. SYN: arterialized blood.
peripheral b.The blood that circulates in arteries and veins as distinguished from the blood present in bone marrow.
reconstituted b.A blood product used in transfusion therapy composed of components of blood (packed red blood cells plus plasma), which have been recombined after their separation and storage.
sludged b.Hemagglutinated blood.
SEE: agglutination.
whole b.Blood that has not been altered or separated into various cellular or fluid constituents after it has been withdrawn from a donor.