Bone Marrow & Blood Cell Formation 1

BONE MARROW & BLOOD CELL FORMATION

Origin of Blood Cells Erythropoiesis > hemopoiesis

Granulopoiesis Thrombopoiesis Lymphopoiesis Monopoiesis

Fetal Hemopoiesis : 1. Mesoblastic Phase 2. Hepatic Phase 3. Myeloid Phase

Mesoblastic Phase : > mesenchyme of the body stalk > yolk sac ( 2nd week AOG ) > primitive erythroblast ( nucleated )

Hepatic Phase : > liver ( 6th week AOG ) > definitive erythroblast ( anucleated ) > later - spleen

Myeloid Phase : > bone marrow ( 4th month AOG )

Bone Marrow : > medullary canals of long bones / spongy bone cavities > 2 types 1. Red bone marrow > hematogenous / active > newborn – all > adult – flat bones , diploe, vertebra, epiphysis of long bones > myeloid and lymphoid functions 2. Yellow bone marrow > adult > reserve hemopoietic tissue > fat storage

Theories : 1. Unitarian or Monophyletic theory 2. Dualistic theory 3. Polyphyletic theory

Summary of erythrocyte maturation. The stippled part of the cytoplasm (on the left) shows the continuous increase in hemoglobin concentration from proerythroblast to erythrocyte. There is also a gradual decrease in nuclear volume and an increase in chromatin condensation, followed by extrusion of a pyknotic nucleus. The times are the average life span of each cell type. In the graph, 100% represents the highest recorded concentrations of hemoglobin and RNA.

Erythropoiesis : > 3 days

Pre-rubricyte

Rubricyte

Normoblast

Granulopoiesis :

Section of red bone marrow with a group of erythropoietic cells (upper right) and a group of neutrophilopoietic cells (lower left). The immature granulocytes shown have mostly azurophilic granules in their cytoplasm and therefore are myelocytes. PT stain. High magnification.

Thrombopoiesis : I. Megakaryoblast II. Promegakaryocyte III. Megakaryocyte

Section of bone marrow showing various stages of megakaryocyte development (1–4), several adipocytes (*), and blood sinusoids (arrowheads). PT stain. Medium magnification.

Lymphocytes:

Monocytes: