Movie - Cardiovascular 3D stage 13
|Stage13-CVS-icon.jpg</wikiflv>||3 Dimensional Reconstruction
Based upon a serial reconstruction from individual embryo slice images. (6 mm pig embryo, approximately Human day 32, Carnegie Stage 13/14 embryo)
The mesoderm contributes structures in the cardiovascular system which is initially laterally symmetrical (left right) and is extensively remodeled in embryonic development. Note the relatively large size and position of the heart and the distribution of individual blood vessels at this early stage of development. Below the animation is a more complete description of this system.
The heart develops from cardiogenic mesoderm, a region of splanchnic mesoderm lying above the buccopharyngeal membrane. Development begins in week 3 with the formation of a pair of heart tubes. These fuse and form a single tube in week 4, as a result of the embryonic folding processes that occur. As the heart grows, septation events occur, transforming it into a 4-chambered pump. Initially, the ventricles develop above the atria; however simultaneous growth and bending of the tube bring the structures into correct position. In humans, the heart begins to beat on day 22-23.
The vascular system of the embryo is formed from blood islands that appear in the extraembryonic mesoderm of the yolk sac and the embryonic mesoderm (primarily splanchnic mesoderm). Both of these clusters fuse together and extend, forming a vast network.
The early circulation has 3 components: Embryonic, Placental and Vitelline. Each of these has its own system of arteries and veins.
- Embryonic – blood from the dorsal aorta enters intersegmental arteries, including the arteries of the pharyngeal arches. The blood returns to the heart via the anterior and posterior cardinal veins.
- Placental – the umbilical arteries receive blood from the aorta. This is carried to the chorionic villi, where exchange occurs with the mother. Waste products are disposed of, nutrients and oxygen are collected, and then the umbilical veins convey the blood to the sinus venosus. A persistent right umbilical vein is thought to be a rare anomaly.
- Vitelline – (not shown) the vitelline arteries branch off the dorsal aortas and enter the yolk sac, covering its entire surface. The vitelline veins return red blood cells from the capillary beds to the sinus venosus, posterior to the heart. The vitelline vessels eventually contribute to the portal system of the liver in the adult.