16.6 Development of the veins



The umbilical system

Quiz

Quiz 17

The umbilical veins bring the nutrient- and oxygen-rich blood from the placental villi via the umbilical cord to the embryo. Normally there exists only one umbilical vein in the umbilical cord: the unpaired umbilical vein. At the caudal rim of the navel, though, it becomes connected to the two intraembryonic umbilical veins, which go laterally from the umbilical coelom to the heart and empty into the two sinus horns with the omphalomesenteric veins that lie medial from them. Fig. 23 - Umbilical venous system
Stage 12 (ca. the 30th day)		  Legend

1
2
3
4
5
6
7
8
9
10 		 First aortic arch
Outflow tract (distal section)
Superior cardinal vein
Inferior cardinal vein
Upper intestinal sinus
Ventricle (middle section)
Sinus venosus
Liver anlage
Umbilical vein
Omphalomesenteric vein

Fig. 23
Heart with major in- and out- flowing vessels.


In the further development the umbilical veins become quickly included in the developing liver, so that they obtain a connection to the liver's capillary plexus. Now the blood from the left and right umbilical vein gets into the sinus venosus directly on the one hand and via the anastomoses in the liver on the other.

The extrahepatic part of the umbilical veins atrophies rather soon 13-14. The blood of the umbilical veins now reaches the sinus venosus mixed with the blood of the omphalomesenteric veins passing through the liver. The posthepatic part of the left omphalomesenteric vein atrophies and the right one takes over all of the blood flowing through the liver. (compare the development of the cardinal vein system interactive diagram)
In parallel a shunt, the ductus venosus, has formed within the liver. It directs a part of the nutrient- and oxygen-rich blood from the umbilical veins directly into the heart so that it reaches organs like the brain as quickly as possible.



Development of the
omphalomesenteric system		  Navigation
1
2
3
4
5
6
7

8

9
10
11
12
13
14
15		 Sinus venosus
Superior cardinal vein
Inferior cardinal vein
Left common cardinal vein
Right umbilical vein
Liver
Anastomose between the left and
right omphalomesenteric vein
Right umbilical vein
(prehepatic)
Left umbilical vein
Right omphalomesenteric vein
Umbilical vein (unpaired)
Vena cava inferior
Ductus venosus
Portal vein
Splenic vein


Stage 13 (32nd d.)

Stage 15 (36th d.)

Stage 18 (44th d.)

Stage 20 (49th d.)











Overview of the illustrations


The prehepatic portion of the right umbilical vein later atrophies completely and all of the placental blood gets to the liver via the left umbilical vein. Following birth, the left umbilical vein is obliterated and the ductus venosus becomes the ligamentum venosum.



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