The portal triad is an area at the liver named after its triangular shape and its three major components: the hepatic artery, the hepatic portal vein, and the hepatic ducts, or bile ducts. The term, however, can be considered a misnomer, since it contains other structures as well. This section of the liver is actually better known by its clinical term, portal hepatis. Other terms include transverse fissure and portal fissure. The portal triad serves as a blood-vessel gateway or entrance of the liver’s hepatic lobule.
The blood vessels that enter the triad are the hepatic artery and hepatic portal vein. The former is sometimes called the hepatic artery proper, or proper hepatic artery, to differentiate it from the common hepatic artery, which is its site of origin. The hepatic artery that forms the triad is responsible for supplying oxygenated blood to the liver via its left and right channels. It is also set apart from the gastroduodenal artery, which is the other branch arising from the common hepatic artery, and supplies oxygenated blood to the stomach as well as the beginning section of the small intestine, called the duodenum.
The portal vein is the other blood vessel that forms the portal triad. Like the hepatic artery, it splits into left and right channels upon reaching the liver, and it supplies nutrient-rich blood to the organ. The portal vein, however, is responsible for most of the blood supply; medical researchers estimate it at 75 percent. Also, it gets the blood from the stomach and small intestine, rather than the heart. The portal vein originates from the union of the superior mesenteric vein and the splenic vein at the neck of the pancreas and has an overall length of about 3 inches (8 centimeters) in adults.
The hepatic ducts go out of the liver to connect with the intestines for the transportation of bile, which is used for digestion. It is divided into the left and right ducts, each of which correspond with the section of the liver they are responsible for draining. The other structures of the portal triad are the lymphatic vessels, which are components of the body’s immune system, and a branch of the vagus nerve, which is one of the nerves that originate from the brain.
A malfunction of the portal triad can cause liver problems such as cirrhosis, and in the most extreme cases, death. A common condition is portal hypertension, which denotes high blood pressure in the hepatic portal vein. This condition can be treated using beta-blockers to reduce the pressure in the vein’s blood flow.