Cardiac Loop Formation
With further development, the heart tube elongates and forms five dilations, from caudal to cranial: sinus venosus, atrium, ventricle, bulbus cordis, and truncus arteriosus.
These dilations will develop into the adult structures of the heart:
On day 23 (week 4th), the heart tube starts to loop and fold. ‘The cranial portion of the tube bends ventrally, caudally, and to the right, and the caudal portion shifts dorsocranially and to the left.
The bending is complete by day 28 and results in:
- Atrium >>> dorsal and cranial
- Ventricle >>> displaced left
- Bulbus cordis >>> inferiorly, ventrally to the right
@ Press on the picture to see related vedio.
The atrioventricular junction develops into atrioventricular canal, which connects the primitive atrium and the primitive ventricle. The bulboventricular sulcus between the ventricle and the bulbus cordis develops into the primary interventricular foramen.