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| == Introduction ==
| | #REDIRECT [[Cardiovascular System - Heart Development]] |
| The heart is the first organ to form in the embryo and lies at the top of the embryonic disc as a simple tube developing in the middle embryonic layer (mesoderm). When this embryonic disc folds, the heart gets carried into the correct anatomical position in the chest cavity.
| | This page has been replaced by [[Cardiovascular System - Heart Development]] |
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| Development of the heart and vascular system begins very early in mesoderm both within (embryonic) and outside (extra embryonic) the embryo. Vascular development therefore occurs in many places, the most obvious though is the early forming heart, which grows rapidly creating an externally obvious cardiac "bulge" on the early embryo. | |
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| Throughout the mesoderm, small regions differentiate into "blood islands" which contribute both blood vessels (walls) and fetal red blood cells.
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| These "islands" connect together to form the first vessels whcih connect with the heart tube.
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| A key aspect of heart development is the septation of the heart into separate chambers. As the embryonic/fetal circulation is different to the neonatal circulation (lung/pulmonary activation), several defects of heart septation may only become apparent on this transition. One septal "defect" occurs in us all, the foramen ovale (between the 2 atria) which in general closes in the neonate over time.
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| The peripheral vasculature can be thought of as 3 aortic/venous circulatory systems:
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| * '''placental system''' develops mainly in the extraembryonic mesoderm of the chorion, receives maternal nutrition, removes embryonic waste and is lost with the placenta at birth
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| * '''vitelline system''' covers the surface of the yolk sac and contributes to the portal system (between gut and liver).
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| * '''embryonic system''' begins symmetrically (L/R) within the embryo, and is extensively remodelled, in particular in the pharyngeal arches, to mature into our cardiovascular system.
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