This document provides an introduction to hematology, including: - Hematopoiesis is the formation of blood cells in the bone marrow and other tissues like the liver and spleen. - In the fetus, hematopoiesis begins in the yolk sac and later the liver, before shifting primarily to the bone marrow. - The bone marrow contains hematopoietic stem cells that differentiate into the various blood cell types through a series of intermediate progenitor cells and maturation stages. - The major blood cell types - red blood cells, white blood cells, and platelets - are derived from hematopoietic stem cells through distinct developmental pathways regulated by growth factors and the bone marrow microenvironment.