125. Development of The Venous System: Primitive Venous Network and Superior Vena Cava

  1. The primitive venous network: the venous system of the embryo consists of a dorsal systemic and double nutritional network by week 4
    1. THE DORSAL SYSTEMIC NETWORK drains the body of the embryo proper and carries all the intraembryonic blood. It is formed by the anterior and posterior cardinal veins which reach the sinus venosus through the common cardinal veins
    2. THE DOUBLE NUTRITIONAL NETWORK carries the extraembryonic blood by way of
      1. The vitelline or omphalomesenteric system carrying blood from the yolk sac toward the heart
      2. The umbilicoallantoic system carrying blood (oxygenated) from the placenta to the embryo
    3. BOTH NETWORKS are initially paired and symmetric, but by a series of cross or transverse anastomoses, they are converted into single major trunks in the right half of the embryo. The left-sided vessels diminish in size and are largely obliterated
  2. Development of the superior vena cava
    1. THE SUPERIOR VENA CAVA has a relatively simple development compared to the inferior vena cava, but is formed somewhat later
      1. In week 8, a large anastomosis (derived from the thymic and thyroid veins) channels the blood from the left anterior (superior) cardinal vein toward the right. This gives rise to the future left brachiocephalic venous trunk
        1. Above the anastomosis, the anterior cardinal veins become the internal jugular veins
      2. The anterior veins of the mandibular region give rise to the external jugular veins
      3. The venous plexuses of the upper limb fuse to form the subclavian vein. The latter originally opens into the posterior cardinal vein, but as the heart shifts somewhat caudally in its development, the subclavian vein finally shifts to open into the anterior cardinal vein.
      4. The left anterior cardinal vein, below the anastomosis, loses its connection with the left common cardinal vein. The part that persists is a short segment which forms the left superior intercostal vein
      5. The left common cardinal vein persists as a very short segment which forms the coronary sinus venosus
      6. The superior vena cava itself is finally formed by the right common cardinal vein and the proximal portion of the right anterior cardinal vein
  3. Malformations of the superior vena cava
    1. MALFORMATIONS are rare. Some of those that are seen are
      1. Left superior vena cava
      2. Double superior vena cava
      3. Abnormal pulmonary venous return which drains into either the superior vena cava or the right atrium

development of the venous system: primitive venous network and  superior vena cava: image #1