Hemopoiesis
Hemopoiesis: How Your Body Makes Blood Cells Why do we need constant blood cell production? Most blood cells live fast and die young. Many white blood cells survive only hours to days; platelets last about a week; red blood cells last around 120 days. To keep you healthy, the body must continually replace these “formed elements.” Negative feedback systems keep RBCs and platelets relatively steady, while white blood cell numbers swing up or down depending on infections, inflammation, and other immune challenges. Where does hemopoiesis happen across life? Hemopoiesis (also called hematopoiesis) is the process of forming blood cells. Early embryo: yolk sac Fetus: liver, spleen, thymus, and lymph nodes Last trimester onward and throughout life: red bone marrow becomes the primary site In newborns, almost all marrow is red and active. With growth, much of the marrow in long bones turns into yellow marrow (fatty and inactive). During severe blood loss, yellow marrow can revert to red an...