Blood pressure is an important measurement of vital functions and results from the pressure that the blood exerts upon the blood vessel containing it. When blood pressure is increased, it is called hypertension, and when it is decreased, it is called hypotension.
When we think of blood pressure, we usually think of the blood pressure within the blood vessels of the systemic circulation, which are the blood vessels connected to the heart, but in reality, it can also mean the blood vessels that are connected to portal circulations.
The portal circulation
Portal circulations are those that form a closed loop without the heart involved. They are found in different sites of the body, but the best well-known one is perhaps the hepatic portal system. The hepatic portal system is the one involving the liver and consists of different blood vessels draining the whole gastrointestinal system. The main function of the hepatic portal system is to make sure that all nutrients and toxins that are absorbed from the gastrointestinal system are not sent directly to the systemic circulation, but rather pass by the liver for processing.
The portal circulation and the systemic one are not completely separated, and they are still connected via a system of blood vessels called portosystemic shunts that connect both of them and only open when the portal blood pressure increases to relieve that pressure. They are located at the lower esophagus (the food tube that connects the mouth to the stomach) as well as around the umbilicus and the lower rectum.