Formed components of blood include red blood cells (RBC’s), white blood cells (WBC’s), and platelets. Red blood cells are denucleated biconcave discs which contain millions of hemoglobin molecules in each RBC. The lifespan for red blood cells is generally 120 days. Each hemoglobin molecule is capable of transporting 4 molecules of oxygen. The lifecycle for RBC’s ends with phagocytosis in either the spleen, liver, or bone marrow. Globin molecules from the hemoglobin are converted to amino acids. The heme molecule (iron containing component of hemoglobin) loses its iron which is transported on a plasma protein (transferrin) as Fe+3 and stored on ferritin protein. (When the iron is needed again for the synthesis of hemoglobin, it is transported back to the bone marrow by transferrin.) Heme minus the iron molecule is converted to biliverdin and subsequently into bilirubin. In the liver, bilirubin is converted into bile and excreted into the duodenum. In the large intestine, bilirubin is converted to urobilinogen and urobilin. The former is excreted in feces and the latter is reabsorbed into the bloodstream and excreted through the kidneys.
White blood cells contribute to the immune response system of the body. They are differentiated into granulocytes and agranulocytes. Among the granulocytes are neutrophils (the body’s first responder in the phagocytosis process in the blood), basophils (release histamines, serotonin, and heparin during inflammatory responses), and eosinophils (release histaminase to control inflammatory responses). The agranulocytes consist of lymphocytes and monocytes. Lymphocytes are differentiated into B-cells, T-cells, and killer cells. B-cells are the primary humoral immune defense against bacteria and antibody formation. T-cells are the primary cell-mediated immune defense against viruses, fungi, transplanted tissue, and cancerous cells. Monocytes are large macrophages that contribute to the phagocytosis process. Monocytes can be either fixed in tissues available for local phagocytosis or wandering in the bloodstream following locations of neutrophil phagocytosis activity.
Platelets (thrombocytes) are denucleated cell fragments that contribute to the hemostasis process in blood vessels. The lifespan for platelets is generally 5-9 days. Hemostasis naturally occurs when the intimal layer of a vascular wall has been damaged. In principle, hemostasis is a natural response to reduce the threat of hemorrhage if a blood vessel has been damaged. The first step is platelet activation by exposed collagen fibers from the damaged intimal vessel wall. Once activated, platelets release thromboxane A2 (a potent vasoconstrictor) and adhere to the vessel wall. The glycoprotein IIb/IIIa receptor sites on platelets attract fibrinogen to create an aggregation of platelets referred to as a platelet plug. The second step involves either the intrinsic pathway or extrinsic pathway for coagulation. The intrinsic pathway begins with activation of factor XII…