16.2 From serial to parallel circulation - the septation of the heart



Introduction


With ca. the 28th day 10 the heart of the embryo begins to beat. Initially this only causes a back and forth movement of the blood to occur, but very soon a directional flow of the blood begins from the inflow tract over the atrium and ventricle part in the conus cordis and the pair of aortic arches. The inflow tract contains oxygen-rich blood from the umbilical veins and a contribution from the omphalomesenteric veins. Fig. 7 - Heart in stage 10
(ca. the 28th day)		  Legend

1
2
3
4

5
6
7
8
9
10		 Endocardial loop
First aortic arch
Foregut
Cardiac jelly in the myocardiac
mantle
Pericardial cavity
Amniotic cavity
Midgut
Septum transversum
Umbilical vein
Omphalomesenteric vein
without definitions
with definitions
Fig. 7
The blood flows into the heart from the paired umbilical and omphalomesenteric veins. It leaves the heart via the pair of aortic arches in order to get into the embryo's blood circulation system.



More info

In the embryo, the first heart contractions can be detected in stage 8 (ca. the 23rd day). In the beginning, the frequency is limited to roughly 70 contractions per minute. Up to the 7th week of pregnancy, though, the frequency increases to 170 - 190 beats /minute and at birth the heart beats at 160 - 180 times per minute.



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