L3.3: Hematopoiesis

• HEMATOPOIESIS

  ● The process of blood cell formation that occurs in red bone marrow (myeloid tissue)

  ● All blood cells are derived from a common stem cell hemocytoblast (“blood cell former”)
• HEMATOPOIESIS

  ● Hemocytoblasts form 2 types of descendants

  ○ Lymphoid stem cell — produces lymphocytes

  ○ Myeloid stem cell — can produce all other formed elements
• FORMATION OF RBCs

  ● Tnable to divide, grow, or synthesize proteins (because anucleate)

  ● Wear out in 100-120 days

  ○ When worn out, RBCs are eliminated by phagocytes in the spleen or liver

  ○ Lost cells are replaced by division of hemocytoblasts in the red bone marrow

  ○ Some components are salvaged for reuse or recycled to their building blocks
• FORMATION OF RBCs

  ● Reticulocytes — young RBCs that enter the blood to become oxygen-transport erythrocytes; still contains rough ER

  ● Erythropoietin — hormone that controls the rate of RBC production

  ○ Kidneys produce most erythropoietin as a response to reduced oxygen levels in the blood

  ○ Homeostasis is maintained by negative feedback from blood oxygen levels
• FORMATION OF RBCs

  ● RBC production is controlled by the ability of the available RBCs to transport enough oxygen to meet the body’s demands, not by its quantity in the bloodstream
• FORMATION OF WBCs AND PLATELETS

  ● Hormones:

  ○ Colony stimulating factors (CSFs) & Interleukins — prompt bone marrow to generate leukocytes

  ○ Thrombopoietin — stimulates the production of platelets from megakaryocytes; produced by the liver
• FORMATION OF WBCs AND PLATELETS

  ● BONE MARROW BIOPSY

  ○ Microscopic examination of cells if bone marrow problems/conditions are suspected ○ A small sample of red marrow from one of the flat bones—ilium or sternum— is withdrawn using a special needle