Blood

About the Blood

Blood is a specialized connective tissue, approximately 5 liters in adults 7 to 8 percent of body weight. It consists of plasma 55 percent and formed elements 45 percent. Plasma is 90 percent water with proteins albumin 60 percent maintaining oncotic pressure, globulins antibodies and transport, fibrinogen clotting, electrolytes, nutrients, hormones, and waste products. Red blood cells erythrocytes are 4.2 to 6.1 million per microliter, biconcave discs 7 micrometers, containing hemoglobin 12 to 17 g dL, carrying 1.34 mL oxygen per gram. They lack nuclei and mitochondria, surviving 120 days. White blood cells leukocytes are 4,500 to 11,000 per microliter: neutrophils 60 percent bacterial defense, lymphocytes 30 percent adaptive immunity B cells antibodies, T cells cellular, NK cells, monocytes 5 percent becoming macrophages, eosinophils parasites and allergy, basophils histamine release. Platelets thrombocytes are 150,000 to 400,000 per microliter, cell fragments from megakaryocytes, forming the initial platelet plug. The clotting cascade intrinsic and extrinsic converge on common pathway producing thrombin, converting fibrinogen to fibrin. ABO blood groups A, B, AB, O are determined by surface antigens, Rh by D antigen.