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(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.


BLOOD COMPOSITION Components of blood and relationship to other body tissues

TYPES OF BLOOD CELLS Cell types found in smears of peripheral blood from normal individuals.; SEE: buffy coat; SEE: plasma; SEE: 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; SEE: cell; SEE: erythrocyte; SEE: leukocyte; SEE: plasma; SEE: 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.


TYPES OF BLOOD CELLS

BLOOD COMPOSITION Components of blood and relationship to other body tissues

BLOOD COMPOSITION Components of blood and relationship to other body tissues

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Citation

TY - ELEC T1 - blood ID - 734910 PB - Taber's Medical Dictionary UR - https://www.unboundmedicine.com/medline/view/Tabers-Dictionary/734910/all/blood ER -