Chapter 17: Blood

Blood performs multiple critical roles including oxygen and nutrient transport, carbon dioxide and metabolic waste removal, regulation of pH and osmotic balance, hemostasis through clotting mechanisms, immune defense against pathogens, and thermoregulation. The chapter establishes that whole blood consists of plasma, a liquid matrix comprising water, proteins such as albumins and fibrinogen, and dissolved electrolytes, along with formed elements including erythrocytes, leukocytes, and platelets. Red blood cells are specialized anucleate biconcave discs optimized for gas exchange, containing hemoglobin molecules with iron-binding heme groups that reversibly bind oxygen to form oxyhemoglobin. The chapter traces hemopoiesis, the developmental process by which hemocytoblasts in red bone marrow differentiate into lymphoid and myeloid stem cell lines, with erythropoietin serving as the primary regulatory hormone during hypoxia. Blood cell recycling occurs when senescent erythrocytes are phagocytosed by macrophages, leading to bilirubin formation and potential jaundice when hepatic clearance is impaired. The chapter addresses immunohematology through blood typing systems, particularly the ABO group based on surface antigens and corresponding plasma antibodies, and the Rh factor system whose incompatibility causes hemolytic disease of the newborn. White blood cells are categorized as granulocytes including neutrophils, eosinophils, and basophils, and agranulocytes including monocytes and lymphocytes, each with distinct immune functions. Hemostasis is described as a three-phase process involving vascular spasm, platelet plug formation, and coagulation cascade mechanisms that convert fibrinogen to fibrin. Finally, the chapter surveys blood disorders spanning nutritional deficiencies like iron-deficiency anemia, genetic conditions including sickle cell disease and hemophilia, infectious diseases affecting blood components, and malignant proliferations such as leukemias.