https://medlabwiki.com/index.php?action=history&feed=atom&title=Hematopoiesis 2026-04-08T16:52:11Z Revision history for this page on the wiki MediaWiki 1.45.3 https://medlabwiki.com/index.php?title=Hematopoiesis&diff=125&oldid=prev 2025-01-08T03:04:21Z

<p>Created page with &quot;Fetal Hematopoiesis # Mesoblastic (yolk sac) phase #* From 19th day of gestation to 2-3 months #* Primitive RBCs formed intravascularly #* Three embryonic hemoglobins produced with very high O2 affinity #** Hb-Gower 1 #** Hb-Gower 2 #** Hb-Portland # Hepatic phase #* From 5-7 weeks gestation, declining until birth #* Liver and spleen produce initially produce cells, eventually continuing in thymus, placenta, kidney, lymph nodes, and bone marrow #* Cells produced extrava...&quot;</p> <p><b>New page</b></p><div>Fetal Hematopoiesis<br /> <br /> # Mesoblastic (yolk sac) phase<br /> #* From 19th day of gestation to 2-3 months<br /> #* Primitive RBCs formed intravascularly<br /> #* Three embryonic hemoglobins produced with very high O2 affinity<br /> #** Hb-Gower 1<br /> #** Hb-Gower 2<br /> #** Hb-Portland<br /> # Hepatic phase<br /> #* From 5-7 weeks gestation, declining until birth<br /> #* Liver and spleen produce initially produce cells, eventually continuing in thymus, placenta, kidney, lymph nodes, and bone marrow<br /> #* Cells produced extravascularly<br /> #* All cell types produced<br /> #* Hemoglobin-F primarily produced (high O2 affinity), some adult hemoglobins (Hb-A) may begin formation<br /> # Myeloid (medullary) phase<br /> #* From 4-5 months onwards<br /> #* Bone marrow primary site of hematopoiesis<br /> #** Mostly active (red) marrow at birth<br /> #* All cell types produced<br /> #* Hemoglobin F and Hemoglobin A produced<br /> <br /> Adult Hematopoiesis<br /> <br /> * Primarily occurs in bone marrow (all cell types)<br /> ** Also produced in lymph nodes, spleen, liver, and thymus<br /> * Red marrow: hematopoietically active<br /> ** 50:50 ratio of active cells to apidose in red marrow<br /> * Yellow marrow: hematopoietically inactive<br /> ** Can revert to red marrow when there is need for more blood cells<br /> * At birth and early childhood, all bones contain red marrow<br /> ** Over time, red marrow replaced with adipose tissue (yellow marrow)<br /> ** At 5-7 years, regression begins with adipose tissue dominating<br /> * Active red marrow located more interior-ly (skull, spine, sterum, ribs, pelvis, proximal ends of long bones, etc.)<br /> * In times of extreme stress, other sites can resume producing blood cells (extramedullary hematopoiesis)<br /> ** Liver, spleen, thymus, lymph nodes, etc.<br /> <br /> Bone Structure<br /> <br /> * Exterior surrounded by cortical bone layer<br /> * Interior contains cavities<br /> ** Trabecular bone, consists of connecting structures<br /> ** Hematopoietic tissue, adipose tissue, and blood vessels are present within the gaps in bone trabeculae<br /> * Red marrow arranged into cords/sheets of cells that are held together by connective tissues<br /> ** Contains variety of blood cell types at various stages of maturation<br /> *** Erythrocytic islands sequester iron for RBC production, located near vessels<br /> *** Megakaryocytes release fragments (platelets)<br /> *** Granulocytes move towards vasculature as they mature<br /> ** Release of cells stimulated by cytokines, and is tightly controlled<br /> ** Also contains apidocytes and other supporting cells (connective tissue, endothelial cells of blood vessels, stromal cells regulating nutrients, other cells secreting signalling cytokines, etc.)<br /> * Yellow marrow adipocytes present throughout red marrow</div>

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