Chapter 2: Erythropoiesis and General Aspects of Anaemia

Erythropoiesis and General Aspects of Anaemia delineates the progression of circulating blood cells from pluripotential stem cells in the marrow, focusing on the specialized role of erythrocytes in oxygen and carbon dioxide transport. The transition from pronormoblasts through various normoblast stages to the eventual extrusion of the nucleus to form a reticulocyte is presented as a highly regulated daily occurrence involving the production of approximately one trillion new cells. Crucially, the hormone erythropoietin, primarily produced by the kidneys, serves as the master regulator of this process, stimulated by hypoxia-inducible factors during periods of low tissue oxygen tension. The text further examines the structure and function of haemoglobin, including the biochemical synthesis of haem in the mitochondria and the importance of the sigmoid oxygen dissociation curve, which is influenced by metabolites like 2,3-diphosphoglycerate. Red cell metabolism, specifically the anaerobic Embden-Meyerhof and hexose monophosphate pathways, is highlighted as essential for maintaining cellular flexibility, generating energy in the form of ATP, and preventing oxidative stress through the production of NADPH. When these systems fail or the rate of red cell loss exceeds production, anaemia results. Anaemia is clinically defined based on age and sex and is classified through red cell indices into microcytic, normocytic, or macrocytic categories. The chapter details how the body adapts to declining haemoglobin through cardiovascular compensation and shifts in oxygen affinity, while also describing the diagnostic utility of reticulocyte counts, blood films, and bone marrow aspirates or trephine biopsies in identifying specific pathologies such as nutritional deficiencies, haemolysis, or ineffective erythropoiesis.