Development of Superior venacavaand Azygous Vein

Anup Pandey

Dept. of Human Anatomy

B.P. Koirala Institute of Health Sciences

Dharan Nepal

Development of Venous system

• In the 5th week, pairs of major veins can be seen.

• The main vein of embryo can be divided into 2 groups:

a. Visceral veins

b. Somatic veins

Visceral and somatic veins.

• Vitelline vein (omphalomesenteric)-carrying blood from yolk sac to sinus venosus.

• Umbilical vein: carry oxygenated blood to the embryo.

• Cardinal vein-drains blood from body wall of the embryo.

Vitelline vein

• arises from capillary plexus of yolk sac, run in each side of duodenum & forms anastomosisaround it.

• with development of liver, proximal part of vitelline and umbilical vein are broken into numerous channel –sinusoid –drain into sinus venosus through rt. and left hepato -cardiac channels.

• Lt horn of sinus venosusretrogress and then Lt hepatocardiac channel also disappear.

• Blood from umbilical and

vitelline vein now enter sinus venosus through Rthepatocardiac channel (common hepatic vein)

How the portal vein is formed??

Development of portal vein

The part of Rt and Lt vitellinevein lying outside the liver undergoes changes –forms portal vein.

It is formed by:

• The lt vitelline vein between entry of superior mesentric and splenic vein.

• The dorsal anastomosis.

• Rt vitelline vein between dorsal anastomosis and cranial ventral anastomosis.

Umbilical veins

• convey oxygenated blood from placenta to the embryo.

• Initially the umbilical veins pass on each side of liver.

• proximal part of both umbilical vein & remainder of the right umbilical vein disappear.

• Only left umbilical vein is left which carries blood from placenta to liver.

• In order to facilitate blood supply some sinusoid enlarge to create direct passage connecting it with the Rthepatocardiac channel–ductus venosus.

• After birth, left umbilical vein & ductus venosus are obliterated to form ligamentum teres hepatis & ligamentum venosumrespectively.

Cardinal veinsConsists of:• Anterior cardinal

• Posterior cardinal

• Common cardinal vein

• During 5th to 7th wk additional veins are formed:

1. Subcardinal veins- formed in relation to the mesonephros, which drain kidneys.

2. Sacrocardinal veins-drain lower extremities

3. Supracardinal veins-Drains the body wall by way of intercostal veins. There is anastomosisbetween right & left system so that blood is channeled from left to right.

Cardinal veins • Form the main venous

drainage system of the embryo.

consists of :• anterior cardinal veins,

which drain the cephalic part of the embryo,

• posterior cardinal veins, which drain the rest of the embryo.

• The anterior and posterior veins join before entering the sinus venosus and form the short common cardinal veins.

Fate of ant. and common cardinal vein

• Superior venacava is derived from-Rt. common cardinal vein & the rt. ant. cardinal caudal to the transverse anastomosis.

• Rt. brachiocephalicvein develops from Rt. anterior cardinal vein cranial to the transverse anastomosis.

• Left brachiocephalicvein: develops from part of the left ant. cardinal vein and transverse intercardinalanastomosis.

• Internal jugular vein: develops from the parts of the ant. cardinal veins cranial to their junction with the subclavianveins.

• External jugular veins: arise as a secondary channel and are derived from the venous plexus in the face.

• Subclavian vein: formed by considerable enlargement of the intersegmental veins in the region of upper limb bud.

• Lt horn of sinus venosusretrogress and these veins persist into adult life as Lt superior Intercostal vein and coronary sinus.

• Lt superior intercostal vein is formed by:

−Left ant.cardinal vein caudal to the transverse anastomosis and most cranial part of the left posterior cardinal vein.

−The 2nd and 3rd intercostalvein drain into it.

• Coronary sinus− Medial part is derived

from- left horn of sinus venosus .

− Lateral part is derived from - proximal part of the left common cardinal vein.

The remaining part of the left common cardinal vein persists as the oblique vein of left atrium.

Clinical correlates Venous system defects:

• Left superior venacava: due to the persistence of the left anterior cardinal vein, and obliteration of the common cardinal vein and anterior cardinal veins on the right side.

• Double superior vena cava:is due to the persistence of the left anterior cardinal vein and failure of the formation of left brachiocephalic vein.

Azygos vein in adults

Azygos system of veins:

consists of:

series of longitudinal veins in each side of body that drain blood from the body wall and move it superiorly to drain into SVC.

Azygos vein

• The veins draining the body wall at first drain into the posterior cardinal vein.

• Their drainage is soon transferred to the longitudinal venous channels – veins of azygosline.

• Cranially these channels drain into the posterior cardinal veins.

• With the retrogression of the left common cardinal vein, the left azygos line loses its communication with posterior cardinal vein

• So the blood of this channel drains into the right azygos line thr the post-aortic anastomosis.

• The azygous vein is formed from

- the vein of the right azygosline.

- the most cranial part of the right posterior cardinal vein thrwhich it opens into the superior venacava.

• The vertical part of the hemiazygos and the accessory hemiazygos vein represent the left azygos line.

• Their horizontal part are formed by the post aortic anatomosis.

Summary • Main veins of the embryo:

visceral vein- vitelline and umbilical vein

somatic vein- cardinal veins

• Formation of portal vein:

a) The lt vitelline vein between entry of superior mesentric and splenic vein.

b) The dorsal anastomosis.

c) Rt vitelline vein between dorsal anastomosisand cranial ventral anastomosis.

• Left horn of the sinus venosus retrogresses and then left hepatocardiac channel also disappear.

• But only the left umbilical vein is left which carries the blood from the placenta to the liver.

• After birth, left umbilical vein & ductus venosus are obliterated to form ligamentum tereshepatis & ligamentumvenosum respectively.

• Superior venacava is derived from

- Rt. common cardinal vein & the rt. ant. cardinal caudal to the transverse anastomosis.

• Azygous vein is formed from - the vein of the right azygos

line.- the most cranial part of the

right posterior cardinal vein thr which it opens into the superior venacava.

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