|Heart Tube Formation|
The origins of the heart tube are clusters of angiogenic cells which are located in the cardiogenic plate. The cardiogenic plate, which is derived from splanchnoplueric mesoderm, is located cranial and lateral to the neural plate.
2. Endocardial Tubes
These angiogenic cell clusters coalesce to form right and left endocardial tubes. Each tube is continuous cranially with a dorsal aorta, its outflow tract, and caudally with a vitteloumbilical vein, its inflow tract.
The lateral and cranial folding of the embryo forces the tubes into the thoracic cavity. As a result, these tubes come to lie closer to each other and begin to fuse in a cranial to caudal direction.
At approximately day 21 they are completely fused, as seen in this animation (32k) and in a scanning electron micrograph.
3. Heart Tube
The newly formed heart tube bulges into the pericardial cavity and is attached to the dorsal wall by a fold of tissue, the dorsal mesoderm. This is a derivative of foregut splanchnoplueric mesoderm. Eventually this will rupture leaving the heart tube suspended in the pericardial cavity anchored cranially by the dorsal aortae and caudally by the vitelloumbilical veins.
As it bulges into the cavity it becomes invested in a layer of myocardium. A layer of acellular matrix, the cardiac jelly, separates the myocardium and the endothelial heart tube.
The newly formed heart tube may be divided into regions. Starting caudally:
Formation of the bulboventricular loop can be visualized in this animation (40k) and in a scanning electron micrograph.
|John A. McNulty||Last Updated: April 14, 1996|
Created: September 25, 1995