Page 10, Early Development, Devel. Physiol., Dr. D. Penney

Differentiation of the Myocardial Wall:

The myocardial wall differentiates, producing trabeculae carnae (sponginess of the wall), papillary muscles, chordae tendineae, etc.

A coronary circulation develops, with venous blood emptying into the right atrium at the coronary sinus. The coronary sinus is guarded by a valve.

Internally, the conducting system composed of the AV junctional tissue and the AV node, the right and left bundle branches, the purkinje fibers, etc. develop. This assures rapid, consistent depolarization of the larger heart. All these changes are essentially complete by 7 weeks.

Finally, the growth of sympathetic and parasympathetic nerves takes place, providing central nervous system control over cardiac activity, and ultimately blood pressure and organ blood perfusion. This latter process is not complete until well after birth.

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