Hematopoiesis and Erythropoiesis

1. Hematopoiesis (hemopoiesis) - the maturation, development and formation of blood cells
• red bone marrow (myeloid tissue) - location of hematopoiesis; in blood sinusoids which connect with capillaries; mainly in axial skeleton and heads of femur & humerus
  
• hemocytoblast (stem cell) - the mitotic precursor to blood cells before differentiation
  

• Differentiation - maturing cell becomes "committed" to being certain type blood cell
  

2. Erythropoiesis - the maturation, development, and formation of Red Blood Cells (erythrocytes)

hemocytoblast -> proerythroblast -> early (basophilic) erythroblast -> late (polychromatophilic) erythroblast -> (hemoglobin) normoblast -> (nucleus ejected when enough hemoglobin) reticulocyte -> (retaining some endoplasmic reticulum) ERYTHROCYTE

hemocytoblast -> reticulocyte 3 - 5 DAYS

reticulocyte -> ERYTHROCYTE 2 DAYS (in blood)

ERYTHROCYTE lifespan 100 - 120 DAYS

(primarily destroyed by macrophages in the spleen)

3. Regulation of Erythropoiesis

• Hormonal controls - erythropoietin is the hormone that stimulates RBC production

DECREASED oxygen level in blood causes KIDNEYS to increase release of erythropoietin

1. Less RBCs from bleeding

2. Less RBCs from excess RBC destruction

3. Low oxygen levels (high altitude, illness)

4. Increased oxygen demand (exercise)

Erythropoietin now genetically engineered and synthesized by AMGEN of Thousand Oaks.

Testosterone can also mildly stimulate production of RBCs in humans

• Iron - essential for hemoglobin to carry oxygen

1. 65% of Fe in body is in hemoglobin
2. liver and spleen store most excess Fe bound to ferritin and hemosiderin
3. Fe in blood bound to transferrin
4. daily Fe loss: 0.9 mg men/1.7 mg women
5. women also lose Fe during menstrual flow

• B-complex Vitamins - Vitamin B12 and Folic Acid essential for DNA synthesis in early mitotic divisions leading to erythrocytes

Category: Pathology Notes