PHY3111 Study Guide - Yolk Sac, Lateral Plate Mesoderm, Haematopoiesis
Document Summary
Final yolk sac: in week 4 of development, organogenesis is progressing. A section of yolk sac becomes surrounded by endoderm, and is ultimately incorporated into the embryonic gut. Any remaining yolk sac is called the final yolk sac". Blood cells: derived from the lateral plate mesoderm - the splanchnic mesoderm. All blood cell types except lymphocytes are produced. Embryonic erythrocytes: differ from adult erythrocytes bc they are large and nucleated. For the first 6 weeks, almost all circulating rbcs are derived from the yolk sac. Blood islands (shown in image to the right): appear in week 3 (day 18). Peripheral cells (angioblasts) become endothelial cells to line blood vessels. Definitive haematopoiesis (adult phase): provides foetus and adult w/ the various cell types that make up blood and generates haematopoietic stem cells (hscs) that will last the lifetime of the individual. Occurs initially in the aorta-gonad-mesonephros (agm) region, ultimately in the liver, placenta, spleen & bone marrow.
