The poal venous system contributes approximately 75% of the blood and 72% of the oxygen supplied to the liver. Which of the following is TRUE about valves in poal venous system?

The poal venous system is without valves and drains blood from the spleen, pancreas, gall bladder, and abdominal poion of the alimentary tract into the liver. Tributaries of the poal vein communicate with veins draining directly into the systemic circulation. These communications occur at the gastroesophageal junction, anal canal, falciform ligament, splenic venous bed and left renal vein, and retroperitoneum. Ref: Geller D.A., Goss J.A., Tsung A. (2010). Chapter 31. Liver. In F.C. Brunicardi, D.K. Andersen, T.R. Billiar, D.L. Dunn, J.G. Hunter, J.B. Matthews, R.E. Pollock (Eds), Schwaz's Principles of Surgery, 9e.