For betynge of veynes is bettre i-knowe in pe vttre parties of bodies pan ynward abd in pe myddel wipynne. TREVISA Higden (Rolls) I. 59., 1387
Development of the venous system
Early development of the veins of the trunk
At 4 weeks, as shown in Figure 2-1 , three sets of veins drain through the sinus horn into the heart: the umbilical veins, the vitelline veins returning blood from the placenta and yolk sac, and the common cardinal veins returning blood from the head and trunk.
Precardinal, postcardinal, and subcardinal veins
The common cardinal vein collects blood from the head through the paired precardinal veins and receives blood from the trunk through the paired postcardinal veins that run dorsal to the urogenital fold and mesonephros ( Fig. 2-2 ).
Subcardinal veins develop parallel and medial to the postcardinal veins . Distally, the umbilical veins fuse, whereas proximally the right umbilical vein withers as the left umbilical vein enlarges. The paired vitelline veins fuse along the yolk stalk , but proximally they remain separate. The right vitelline vein becomes dominant as the intervitelline anastomosis forms at the site of the future liver.
Umbilical and vitelline veins
The proximal section of the left umbilical vein persists to bring fresh blood through the ductus venosus to the inferior vena cava. (In the adult, the remnant of the left umbilical vein becomes the round ligament of the liver.)
The vitelline veins join to form the portal vein and part of the inferior vena cava. As a result, blood carried by the three original systems now returns into the right sinus horn through the original right vitelline and right and left common cardinal veins , vessels that will form part of the inferior vena cava ( Fig. 2-3 ).
Development of the inferior vena cava
In a description of the basic developmental pattern of the venous system in forming the inferior vena cava, it must be emphasized that not only are the steps in its formation below the kidneys not yet fully understood but also many aberrations from the standard pathway occur.
The postcardinal veins drain the caudal portion of the embryo into the common cardinal veins , which, at the level of the heart, form the sinus venosus ( Fig. 2-4 ). Caudally, they are connected by the important interpostcardinal anastomosis . The subcardinal veins have developed to form a second system, one that lies medial to the postcardinal veins in the trunk and forms multiple connections with them. In addition, the intersubcardinal anastomoses have formed between the right and left subcardinal veins, a complex that is destined to become the renal collar.
Subcardinal and supracardinal veins
The proximal end of the right subcardinal vein joins the hepatic portion of the hepatocardiac vein to form the hepatic and the subhepatic segments of the inferior vena cava.
One more set of veins is formed. The supracardinal veins (in black) lie dorsal to the postcardinal veins and run parallel with them distally to join the interpostcardinal anastomosis ( Fig. 2-5 ). These veins connect proximally with the intersubcardinal anastomosis via the supracardinal-subcardinal anastomosis .
Regression of the postcardinal and supracardinal veins
Cephalad to the interpostcardinal anastomosis, the postcardinal veins regress. To compensate for the reduced drainage, the supracardinal veins enlarge up to their connection with the intersubcardinal anastomosis. The supracardinals remain minor vessels beyond that juncture.
The increased blood flow arriving at the intersubcardinal anastomosis from the now enlarged right supracardinal vein is carried by the similarly enlarged proximal portion of the right subcardinal vein ( Fig. 2-6 ). Thus, the main venous pathway becomes: interpostcardinal anastomosis—supracardinal veins—intersubcardinal anastomosis—right subcardinal—hepatocardiac vein—heart.
Dominance of the right subcardinal vein
The function of the postcardinal veins cranial to the interpostcardinal anastomosis has been assumed by the subcardinal and supracardinal veins. The right supracardinal vein will become dominant, constituting the inferior vena cava caudal to the intersubcardinal anastomosis into which it drains. Cranial to this point, the supracardinal veins have become separated to form the azygos veins.
The subcardinal veins have begun to position themselves as the gonadal veins emptying into the intersubcardinal anastomosis , which, in turn, is destined to become the left renal vein . Proximally, the right subcardinal vein continues to be the main conduit as the left subcardinal vein becomes an adrenal vein ( Fig. 2-7 ).
After the postcardinal veins have degenerated, the lower poles of the metanephroi are free to rotate laterally and ascend as the body straightens and lengthens (see Fig. 12-6 ).
Composition of the inferior vena cava
The cranial segment of the inferior vena cava (above the renal veins) forms when the left supracardinal vein regresses. This leaves the right subcardinal segment as the only channel connecting with the hepatocardiac venous contribution, which, in turn, joins the heart. The junction for the renal, adrenal, and gonadal veins is provided by the intersubcardinal anastomosis ( Fig. 2-8 ).
The caudal portion of the inferior vena cava is derived from the right supracardinal segment . The common iliac veins are formed from the postcardinal veins through the persistence of the interpostcardinal anastomosis.
Table 2-1 compares the embryonic with the adult venous system.
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