Development of Superior venacavaand Azygous VeinAnup PandeyDept. of Human AnatomyB.P. Koirala Institute of Health SciencesDharan Nepal
Development of Venous system• In the 5th week, pairs ofmajor veins can beseen.• The main vein ofembryo can be dividedinto 2 groups:a. Visceral veinsb. Somatic veins
Visceral and somatic veins.• Vitelline vein(omphalomesenteric)-carrying blood from yolk sacto sinus venosus.• Umbilical vein: carryoxygenated blood to theembryo.• Cardinal vein-drains bloodfrom body wall of theembryo.
Vitelline vein• arises from capillaryplexus of yolk sac, run ineach side of duodenum& forms anastomosisaround it.• with development ofliver, proximal part ofvitelline and umbilicalvein are broken intonumerous channel –sinusoid –drain intosinus venosus throughrt. and left hepato -cardiac channels.
• Lt horn of sinus venosusretrogress and then Lthepatocardiac channelalso disappear.• Blood from umbilical andvitelline vein now entersinus venosus through Rthepatocardiac channel(common hepatic vein)
Development of portal veinThe part of Rt and Lt vitellinevein lying outside the liverundergoes changes –forms portal vein.It is formed by:• The lt vitelline veinbetween entry of superiormesentric and splenic vein.• The dorsal anastomosis.• Rt vitelline vein betweendorsal anastomosis andcranial ventralanastomosis.
Umbilical veins• convey oxygenatedblood from placenta tothe embryo.• Initially the umbilicalveins pass on each sideof liver.• proximal part of bothumbilical vein &remainder of the rightumbilical veindisappear.
• Only left umbilical vein is leftwhich carries blood fromplacenta to liver.• In order to facilitate bloodsupply some sinusoid enlargeto create direct passageconnecting it with the Rthepatocardiac channel–ductus venosus.• After birth, left umbilical vein& ductus venosus areobliterated to formligamentum teres hepatis &ligamentum venosumrespectively.
• During 5th to 7th wkadditional veins are formed:1. Subcardinal veins- formed inrelation to the mesonephros,which drain kidneys.2. Sacrocardinal veins-drainlower extremities3. Supracardinal veins-Drainsthe body wall by way ofintercostal veins.There is anastomosisbetween right & left systemso that blood is channeledfrom left to right.
Cardinal veins• Form the main venousdrainage system of theembryo. consists of :• anterior cardinal veins,which drain the cephalicpart of the embryo,• posterior cardinal veins,which drain the rest of theembryo.• The anterior and posteriorveins join before enteringthe sinus venosus and formthe short common cardinalveins.
Fate of ant. and common cardinal vein• Superior venacava isderived from-Rt.common cardinal vein &the rt. ant. cardinalcaudal to the transverseanastomosis.• Rt. brachiocephalicvein develops from Rt.anterior cardinal veincranial to the transverseanastomosis.
• Left brachiocephalicvein: develops from partof the left ant. cardinalvein and transverseintercardinalanastomosis.• Internal jugular vein:develops from the partsof the ant. cardinal veinscranial to their junctionwith the subclavianveins.
• External jugular veins:arise as a secondarychannel and are derivedfrom the venous plexusin the face.• Subclavian vein: formedby considerableenlargement of theintersegmental veins inthe region of upper limbbud.
• Lt horn of sinus venosusretrogress and these veinspersist into adult life as Ltsuperior Intercostal veinand coronary sinus.• Lt superior intercostal veinis formed by:−Left ant.cardinal vein caudalto the transverseanastomosis and mostcranial part of the leftposterior cardinal vein.−The 2nd and 3rd intercostalvein drain into it.
• Coronary sinus− Medial part is derivedfrom- left horn ofsinus venosus .− Lateral part is derivedfrom - proximal partof the left commoncardinal vein.The remaining part ofthe left commoncardinal vein persistsas the oblique vein ofleft atrium.
Clinical correlates Venous system defects:• Left superior venacava: dueto the persistence of the leftanterior cardinal vein, andobliteration of the commoncardinal vein and anteriorcardinal veins on the rightside.• Double superior vena cava:is due to the persistence ofthe left anterior cardinalvein and failure of theformation of leftbrachiocephalic vein.
Azygos vein in adultsAzygos system of veins:consists of:series of longitudinal veinsin each side of body thatdrain blood from thebody wall and move itsuperiorly to drain intoSVC.
Azygos vein• The veins draining thebody wall at first drain intothe posterior cardinal vein.• Their drainage is soontransferred to thelongitudinal venouschannels – veins of azygosline.• Cranially these channelsdrain into the posteriorcardinal veins.
• With the retrogression ofthe left common cardinalvein, the left azygos lineloses its communicationwith posterior cardinalvein• So the blood of thischannel drains into theright azygos line thr thepost-aortic anastomosis.
• The azygous vein is formedfrom- the vein of the right azygosline.- the most cranial part of theright posterior cardinal vein thrwhich it opens into thesuperior venacava.• The vertical part of thehemiazygos and the accessoryhemiazygos vein represent theleft azygos line.• Their horizontal part areformed by the post aorticanatomosis.
Summary• Main veins of the embryo:visceral vein- vitelline and umbilical veinsomatic vein- cardinal veins• Formation of portal vein:a) The lt vitelline vein between entry of superiormesentric and splenic vein.b) The dorsal anastomosis.c) Rt vitelline vein between dorsal anastomosisand cranial ventral anastomosis.
• Left horn of the sinus venosus retrogressesand then left hepatocardiac channel alsodisappear.• But only the left umbilical vein is left whichcarries the blood from the placenta to theliver.
• After birth, leftumbilical vein &ductus venosus areobliterated to formligamentum tereshepatis & ligamentumvenosum respectively.
• Superior venacava is derivedfrom- Rt. common cardinal vein &the rt. ant. cardinal caudal tothe transverse anastomosis.• Azygous vein is formed from- the vein of the right azygosline.- the most cranial part of theright posterior cardinal veinthr which it opens into thesuperior venacava.