VAN 211: Veterinary Histology and Embryology (2+2)

VEINS

• All the veins of the body develop as modifications of the ground plan present in the developing embryo.
• The plan may be outlined briefly as consisting of:
• Umbilical veins,
• Vitelline veins,
• Anterior cardinal veins,
• Posterior cardinal veins,
• Supracardinal veins and
• Sub-cardinal veins and all the six veins are paired.
• The proximal ends of vitelline and umbilical veins are absorbed by the developing liver of form the portal system. The mesenteric veins draining the venous blood from the gut on enter the liver, persists as the portal vein.
• The anterior cardinal veins drain the venous blood from the head and neck. The posterior, sub and supra-cardinal veins drain the venous blood from the posterior parts of the body.
• The cranial segment of the anterior cardinal is transformed into the venous sinuses of the dura mater and the cervical segment persists as the internal jugular form which sprouts the external jugular. The thoracic segments of the anterior cardinals unite to form the anterior vena cava.
• The posterior cardinals degenerate without contributing anything except a small proximal part of the azygos vein. The sub-cardinals unite and are transformed into the posterior vena cava. The supra-cardinals are transformed into the azygos vein on the right and vena hemizygous on the left side.