Hepatic Portal System

The veins draining the digestive viscera empty into the hepatic portal vein. This vein carries the blood into the liver’s specialized capillaries, called sinusoids .
In the liver, bacteria, toxins and other "nasties" are removed. Some nutrients are removed for usage in the liver, while others are "packaged" or "modified" before being released to the rest of the circulatory system through the hepatic veins
The hepatic veins enter the inferior vena cava.

Shock

Hypovolemic : the most common type, due to large scale blood loss or loss of blood volume. The heart rate increases (resulting in a weak pulse), intense vasoconstriction occurs, and pressure usually decreases, but only if volume loss continues.
Vascular : blood volume is normal and constant, but poor circulation arises due to extreme vasodilation. Rapidly falling blood pressure is the main symptom. Septicemia is the most common cause (hence the alternative name, septic shock ), though it can also be caused by autonomic failure or disruption ( neurogenic shock).

Anaphylactic shock is a type of vascular shock brought on by an acute allergic reaction.

Cardiogenic : pump failure. The heart is very weak.
Orthostatic : astronauts returning to Earth experience this. Zero g allows an upward shift of body fluids, but a return to atmosphere results in a sudden pooling. The face and eyes get puffy and the legs "shrink." The uneven blood pressure triggers baroreceptors and hastens fluid loss resulting in diarrhea.