Basic - Primitive Heart Tube
| Begin Basic | Primitive Heart Tube | Embryonic Heart Divisions | Vascular Heart Connections |
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The heart is the first organ to function within an embryo. It starts to function at the beginning of the fourth week when the nutritional and oxygen requirements of the growing embryo can no longer be met by diffusion from the placenta. The heart initially forms from two tubes located bilaterally (on either side) of the trilaminar embryo in the cranial (head) region. The image on the right shows these primitive tubes developing in an embryo approximately 18 days after conception.
When looking down at this early embryo, you can see multiple blood islands dispersed throughout the embryo. These will form the early blood vessels. At the most cranial end of the embryonic disc, these blood islands are actually the primitive heart tube. From the side you can see one of the heart tubes and heart cavity developing in this position.
Embryonic Folding
The disc-like embryo then undergoes a process of folding, in which both the cranial and lateral parts of the embryo fold ventrally (forwards). This brings the heart-forming region to a ventral (frontal) position. The following animation shows the development of the heart tubes and how embryonic folding brings them to fuse in the midline.
<Flowplayer height="540" width="720" autoplay="true">Heart folding 002.flv</Flowplayer>
