VEINS ASSOCIATED WITH HEART Dr. Mujahid Khan

Development of Veins Three paired veins drain into the tubular heart of a four week old embryo Vitelline veins return poorly oxygenated blood from the yolk sac Umbilical veins carry well-oxygenated blood from the primordial placenta Common cardinal veins return poorly oxygenated blood from the body of the embryo

Vitelline Veins The vitelline veins follow the yolk stalk into the embryo Yolk stalk is a narrow tube connecting the yolk sac with the midgut After passing through the septum transversum the vitelline veins enter the venous end of the heart, the sinus venosus

Vitelline Veins As the liver primordium grows into the septum transversum, the hepatic cords anastomose around preexisting endothelium-lined spaces These spaces, the primordia of the hepatic sinusoids later become linked to the vitelline veins The hepatic veins form from the remains of the right vitelline vein in the region of the developing liver The portal vein develops from an anastomotic network formed by the vitelline veins around the duodenum

Umbilical Veins The umbilical veins run on each side of the liver and carry well-oxygenated blood from the placenta to the sinus venosus As the liver develops the umbilical veins lose their connection with the heart and empty into the liver The right umbilical vein disappears during the 7th week Now the left umbilical vein is the only vessel carrying well-oxygenated blood from the placenta to the embryo

Umbilical Veins The right umbilical vein and the caudal part of the left umbilical vein between the liver and the sinus venosus degenerate The persistent caudal part of the left umbilical vein becomes the umbilical vein It carries all the blood from the placenta to the embryo

Umbilical Veins A large venous shunt, the ductus venosus develops within the liver and connects the umbilical vein with the inferior vena cava The ductus venosus forms a bypass through the liver This enables most of the blood from the placenta to pass directly to the heart without passing through the capillary networks in the liver

Cardinal Veins The cardinal veins constitute the main venous drainage system of the embryo The anterior and posterior cardinal veins drain cranial and caudal parts of the embryo The anterior and posterior cardinal veins join the common cardinal veins which enter the sinus venosus

Cardinal Veins During the eighth week the anterior cardinal veins become connected by an anastomosis This anastomosis shunts blood from the left to the right anterior cardinal vein This shunt becomes the left brachiocephalic vein when the caudal part of the left anterior cardinal vein degenerates Superior vena cava forms from the right anterior cardinal vein and the right common cardinal vein

Posterior Cardinal Veins The posterior cardinal veins develop primarily as the vessels of the mesonephroi and largely disappear with these transitory kidneys The only adult derivatives of the posterior cardinal veins are the root of the azygos vein and the common iliac veins

Subcardinal & Supracardinal Veins The subcardinal and supracardinal veins gradually replace and supplement the posterior cardinal veins The subcardinal veins appear first They are connected with each other through the subcardinal anastomosis and with the posterior cardinal veins through the mesonephric sinusoids The subcardinal veins form the stem of the left renal veins, suprarenal veins, gonadal veins and a segment of IVC

Subcardinal & Supracardinal Veins The supracardinal veins are the last pair of vessels to develop They become disrupted in the region of the kidneys Cranial to this they become united by an anastomosis that is represented in the adult by azygos and hemiazygos veins Caudal to the kidneys the left supracardinal vein degenerates The right supracardinal vein becomes the inferior part of the IVC

Inferior Vena Cava The inferior vena cava forms during a series of changes in the primordial veins of the trunk This occurs as blood returning from the caudal part of the embryo is shifted from the left to the right side of the body The IVC is composed of four main segments

Inferior Vena Cava A hepatic segment derived from the hepatic vein (proximal part of right vitelline vein) and hepatic sinusoids A prerenal segment derived from the right subcardinal vein A renal segment derived from the subcardinal supracardinal anastomosis A postrenal segment derived from the right supracardinal vein