Which of the following statements concerning the circulatory system is true?

A poal vein connects one capillary bed to another. In humans, the hepatic poal vein connects the intestinal capillaries with the sinusoids of the liver. The blood, along with blood from the proper hepatic aery, enters the central vein after passing through the sinusoids, and then enters the hepatic veins and the inferior vena cava. The direction of blood flow through an aery is determined by the pressure gradient and may change from moment to moment. Not all veins have valves. For example, the poal vein and all of the veins that drain into it do not have valves. Valves are most prominent in the veins of the limbs. Ref - Harrison&;s internal medicine 20th edition .