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zoo 19th lecture

zoo 19th lecture - Week Five December 3-5 Formation of the...

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Week Five: December 3-5 Formation of the vertebrate heart - Heart is the first functional organ in the embryo - Formed by the hypomere mesoderm (lateral plate mesoderm) – specifically the splancnic mesoderm - Presumptive primordia exist as a pair of tissues on each side of the embryo. Initially there are two functional hearts. The primordia pushes them together to form the one heart. - Primordia migrate in a ventral fashion to fuse and give rise to the simple tube form of the heart Heart - Primordia show up on either side of the neural tube. There is endoderm underneath this that will be split into anterior and posterior endoderm. Pharyngeal area of the endoderm has to be present for the heart to differentiate. Formation of the heart in the chick - Heart forms as paired tubes right and left – induction of the cardia bifida - There are two regions on each side of the notochord and neural tube that will differentiate themselves out as the cardiac primordia. These primordia will arise as angiogenic cell clusters. - Angiogenic clusters separate from the splanchnic sheet – become mesenchymal cells and separate from the heart. These clusters condense to form not only the epimyocardium of the heart, but also the endocardial primordium (tubes that are initially separate from each other). The impermeable membrane prevents them from coming together forming cardia bifida with 2 functional hearts.
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Chick heart continued - The myocardium will fuse around the endocardial tube. Very early, there are two separate tubes separated by the septum that will eventually fuse into one tube surrounded by epimyocardium. Cell Movements - Individual cells separate from the splanchnic mesoderm – become the endocardial tube (inner lining of the heart) - Sheet splanchnic mesoderm will fold around the endocardial tube to form the epimyocardium - Movements are under the influence of and induced by the pharyngeal endoderm.
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