Venous SystemVeins of primitive cardiovascular system at 4th week which drain into primitive heart include three pairs: (i) vitelline veins, (ii) umbilical veins and (iii) common cardinal veins. However, during 5th to 7th weeks, a number of additional pairs of veins are formed which include: (i) subcardinal veins, (ii) sacrocardinal veins and (iii) supracardinal veins. All these veins can be divided into three groups:-
- Vitelline veins
- Infrahepatic part: Derivatives of this part are portal vein and superior mesenteric vein.
- Intrahepatic part: Derivatives of this part are intrahepatic branches of portal vein and tributaries of hepatic vein.
- Suprahepatic part: This part forms the right and left hepatocardiac channels. Left hepatocardiacchannel disappears and right hepatocardiac channel (common hepatic vein) persists as hepatic segment of inferior vena cava.
- Umbilical veins
- Umbilical veins develop in the chorionic sac (primordial placenta), travel in umbilical cord and drain into right and left horns of sinus venosus.
- Whole of the right umbilical vein and proximal part of left umbilical disappear. The distal part of umbilical vein serves to carry oxygenated blood from placenta to fetus. Blood carried by umbilical vein course through to join portal vein. The ductus venosus is a bypass shunt between portal and IVC. Most of the umbilical venous blood shunts through the ductus venosus to IVC. After birth, left umbilical vein is obliterated to form ligamentum teres (of liver) and ductus venosus is obliterated to form ligamentum venosum.
- Cardinal system of veins
- Embryonic systems (three in number)
- Cardinal venous system
- Subcardinal venous system
- Supracardinal venous system
- Transverse anastomoses between embryonic venous system (four in number)
- Brachiocephalic anastomosis between right and left anterior cardinal veins.
- Azygous anastomosis between right and left supracardinal veins.
- Renal anastomosis between right and left subcardinal veins.
- Iliac anastomosis between caudal ends of two posterior cardinal veins.
- Embryonic systems (three in number)
Common Cardinal Veins
Common cardinal veins are formed by anterior and posterior cardinal veins. Right and left common cardinal veins drain into right and left horn of sinus venosus, respectively.
- Anterior cardinal veins drain the blood from cranial part (head and neck and upper limb) of fetus, and join with posterior cardinal vein to form common cardinal vein. Tributaries of anterior cardinal veins are cervical (1 to 7) intersegmental veins. Oblique cross connection (brachiocephalic anastomosis) occurs between two anterior cardinal veins.
- Posterior cardinal veins drain lower part. At their cephalic end they unite with anterior cardinal vein to form common cardinal veins and at their caudal end they make a transverse anastomosis (iliac anastomosis). Tributaries of posterior cardinal vein are 11 thoracic and 5 lumbar intersegmental veins.
Subcardinal veinsThe sub cardinal veins are formed in relation to urogenital ridges and mainly drain the developing kidney. Renal anastomosis (inter-subcardinal anastomosis) develops between two subcardinal veins. Cranial part of right subcardinal vein also establishes an anastomosis with right hepatocardiac channel, and this anastomosis channel forms part of hepatic segment of IVC,
SupracardinaI veinsSupracardinal veins are longitudinal veins which communicate cranially and caudally with posterior cardinal veins. Azygous anastomosis develops between two supracardinal veins.
Derivatives of anterior cardinal venous system are:-
- Superior vena cava (SVC) is derived from (i) right anterior cardinal vein (proximal to brachiocephalic anastomosis), and (ii) right common cardinal vein.
- Right brachiocephalic vein is formed by right anterior cardinal vein (part which lies between right 7th cervical intersegmental vein and brachiocephalic anastomosis).
- Left brachiocephalic vein is formed by brachiocephalic anastomosis (between two anterior cardinal veins).
- Subclavian veins are formed by 7th cervical intersegmental vein.
- Internal jugular veins are formed by anterior cardinal veins (part which lies cranial to their junction with 7 cervical intersegmental veins).
- External jugular veins arise as secondary channel (not derived from anterior cardinal veins).
- Left superior intercostal vein is formed by regressed part of left anterior cardinal vein (caudal to transverse anastomosis) and cranial part of posterior cardinal vein.
- Vertebral veins are developed by longitudinal anastomosis between C1 to C7 intersegmental veins and intercostal veins
Derivatives of posterior cardinal veins, subcardinal veins and supracardinal veins are:
- Inferior vena cava is derived from :-
- Hepatic segment of IVC is derived from (i) right hepatocardiac channel, and (ii) anastomotic channel Between sub cardinal vein and right hepatocardiac channel.
- Renal segment of IVC is derived from right sub cardinal vein. This part receives both renal and suprarenal veins.
- Post renal segment of IVC (major part of IVC) is formed by (i) anastomosis between right supracardinal and subcardinal veins, (ii) right supracardinal vein (lower part), and (iii) right posterior cardinal vein (lowest part).
- Gonadal veins develop from subcardinal veins (distal part below inter-subcardinal or renal anastomosis).
- Suprarenal veins develop from subcardinal veins (proximal part above inter-subcardinal or renal anastomosis).
- Right common iliac vein is derived from right posterior cardinal vein (most caudal part).
- Left common iliac vein develops from transverse anastomosis between lower ends of posterior cardinal veins.
- Right renal vein is a mesonephric vein that drains into renal segment of IVC (which is derived from upper part of right subcardinal vein).
- Left renal vein develops from three sources:
- mesonephric vein (drain into left subcardinal vein),
- left subcardinal vein (small part), and
- pre-aortic intersubcardinal anastomosis.
Azygous system of veins
- Azygos vein develops from right supracardinal vein and cranial part of right posterior cardinal vein.
- Hemiazygous vein develops from left supracardinal veins.
- Transverse azygos vein develops from azygos anastomosis (transverse anastomosis between supracardinal veins).
Developmental anomalies of veins
- Anomalies of SVC
- Left superior vena cava is formed when left anterior cardinal and common cardinal veins persist and the right ones obliterate. Left SVC opens into right atrium through the coronary sinus.
- Double superior vena cava occurs due to persistence of left anterior cardinal vein. The right SVC opens directly into right atrium while left one opens through coronary sinus.
- Anomalies of IVC
- Absence of inferior vena cava above renal veins occurs when the anastomotic channel between right subcardinal vein and right Hepatocardinal channel fails to develop.
- Double inferior vena cava is formed below renal veins due to persistence of both the subcardinal and supracardinal veins below the kidney.
- Left inferior vena cava, i.e. infra renal part of IVC is formed on left side instead of right.
- Preureteric IVC is formed when part of IVC develops from subcardinal vein (which lies anterior to ureter) instead of supracardinal vein (which lies posterior to ureter).