Vena cava O a. vessel that empties into the right atrium
O b. formation of a blood clot in a vessel
O c. structure that keeps fluid moving forward
O d. central opening of a vessel
O e. lower, pointed region of the heart

The superior vena cava is the large vein which returns blood to the heart from the head, neck and both upper limbs. The inferior vena cava returns blood to the heart from the lower part of the body. The return of blood via the vena cava can be compromised and cause disease. (Take that info and see if it helps)