EMBRYONIC DEVELOPMENT & STEM CELL COMPENDIUM
EMBRYONIC DEVELOPMENT & STEM CELL COMPENDIUM
21. Week 3 of Development: Cardiovascular System Development
Review of MEDICAL EMBRYOLOGY Book by BEN PANSKY, Ph.D, M.D.
- Introduction: early cardiovascular system formation can be related to the absence of a significant amount of yolk material in the ovum and yolk sac with the need for vessels to carry both nutrient materials and oxygen
- Angiogenesis or blood formation begins in the extraembryonic mesoderm of the yolk sac, connecting stalk, and chorion during days 13-15. The embryonic vessels begin to develop approximately 2 days later
- MESENCHYMAL CELLS or angioblasts aggregate to form isolated masses and cords called blood islands
- Spaces accumulate in the islands, angiob1asts arrange themselves around the cavities to form the primitive endothelium, then isolated vessels fuse to form networks of endothelial channels
- Vessels continue to extend into adjacent areas by endothelial budding and fusion with other vessels being formed independently
- Blood cells and primitive plasma develop from the endothelial cells as the vessels develop on the allantois and yolk sac
- BLOOD FORMATION begins in week 5, occurring in various portions of the embryonic mesenchyme, particularly in the liver, then later in the spleen, bone marrow, and lymph nodes
- MESENCHYMAL CELLS around the primitive endothelial vessels differentiate into the muscles and connective tissue of the blood vessels
- THE PRIMITIVE ENDOTHELIAL CARDIAC TUBES form from mesenchymal cells in the cardiogenic area
- Longitudinally paired endothelial channels, the heart tubes, develop before the end of week 3 and begin to fuse into the primitive heart tube
- By day 21, the paired tubes link up with blood vessels in the embryo, connecting stalk, chorion, and yolk sac to form a primitive cardiovascular system. The cardiovascular system is the first organ system to reach a functional state
- Blood circulation usually is started by the end of week 3
