This text provides a comprehensive overview of the physiology and pathophysiology of red blood cells (RBCs), emphasizing their critical role in oxygen transport and the disorders that affect their function. It covers the process of RBC synthesis, the structure and function of hemoglobin, and the various types of anemias, including those caused by blood loss, iron deficiency, vitamin B12 deficiency, folic acid deficiency, and bone marrow failure. The text also explores the mechanisms behind hemolytic anemias and discusses the implications of various hemoglobinopathies, such as sickle cell anemia and thalassemia. Additionally, it examines the complications of lead poisoning and transfusion reactions, along with the causes, symptoms, and treatments of different types of red blood cell disorders.