Lecture Thursday August 23: Embryology Heart and Lungs

Fate of five dilations of the primitive heart tube




Truncus arteriosus: (ventral aorta) forms aorta and pulmonary trunk by formation of the aorticopulmonary (AP) septum.
Bulbus cordis: forms conus arteriosus (smooth part of right ventricle) and aortic vestibule (smooth part of left ventricle).
Primitive ventricle: forms trabeculated part of left ventricle.
Primitive atrium: forms trabeculated part of right and left atrium.
Sinus venosus: forms sinus venarum (smooth part of right atrium), coronary sinus, and oblique vein of left atrium.

HEART LOOPING
The single heart tube loops to the right, thus initiating the transformation of the heart into a complex 4-chamber organ. In the process of looping the sinus venosus and atria acquire a more dorsal position to the ventricle and bulbus cordis.

HEART SEPTATION
1. Separation of the atria from the ventricles and formation of the atrioventricular canals (future AV valves):
Endocardial Cushions

2. Separation of the atria:
Septum Primum with an opening called Foramen Secundum
Septum Secundum with an opening called Foramen Ovale
Blood flow: into right atrium > through Foramen Ovale > against septum Primum and through septum Secundum into left atrium. The two septa fuse after birth otherwise Atrial Septal Defect

3. Separation of the ventricle:
Muscular interventricular septum grows from base of ventricles to Endocardial cushions
Membranous portion forms from inferior ends of spiraling contotruncal ridges

4. Septation of truncus arteriosus:
Spiraling conotruncal ridges
(Conotruncal ridges = aorticopulmonary septum = bulbar ridges = truncal ridges)

FETAL CIRCULATION
Goal is to bypass the liver and lungs. Remember ductus venous, Foramen Ovale and ductus arteriosus

LUNG DEVELOPMENT
Epithelium from endoderm of gut tube
All other tissue components from splanchnic mesoderm
Tracheoesophageal septum separates trachea from esophagus and can lead to abnormalities from partial separation.

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