12.11.2011
KNOW ABOUT SUPERIOR VENACAVA
Posted on 7:45 PM by know about heart
Superior venacava is the large venous channel, which drains blood from the upper part of the body into the right atrium. It has no valve.
Formation:
It is formed by the union of right and left brachiocephalic veins behind the lower border of the first costal cartilage close to the sternum. Length=7 cm. From the beginning. It passes vertically downwards and opposite the 2nd costal cartilage it pierces the fibrous pericardium.
Termination: It terminates by opening into the upper part of right atrium behind the third right costal cartilage.
Relations:
A) Anterior:
i) Right internal thoracic vessel
ii) Anterior border of right lung and pleura
B) Posterior
a) Trachea and right vagus nerve
b) Root of the right lung.
C) Medial:
i) Ascending aorta
ii) Brachiocephalic trunk
D) Lateral:
i) Phrenic nerve
ii) Right pleura and lung
Tributaries:
i) Right and left brachiocephalic veins
ii) Azygos vein
iii) Pericardial and mediastinal veins.
Development: Extrapericardial part or the upper half of superior venacava up to the opening of the azygos vein develops from the lower part of right anterior cardinal vein. Intracardial part or the lower half, below the opening of azygos vein develops from the right common cardinal vein.
If superior venacaval obstruction occur above the opening o[f the azygos vein, the venous blood of the upper half of the body is returned through the azygos vein and the superficial veins are dilated on the chest up to the costal margin.
But when superior venacanal obstruction occur below the opening of the azygos veins, the blood is returned through the inferior venacava via the femoral veins. Then the superficial veins are dilated both the chest and abdomen up to saphenous opening in the thigh. The signs of superior venacaval obstruction are the first to appear in mediastinal syndrome.
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