Introduction

A portal system is characterised by veins that begin and end in capillaries. It transports nutrient-rich blood to the liver, where it is purified before being transported to the heart.

The portal vein (PV) is the main vessel in the portal venous system, transporting blood from the gastrointestinal tract and spleen to the liver.

A portal venous system is one where veins connect two capillary beds, or in other words, draining one organ/organ system and transferring into another, instead of returning to the heart. Many people are only aware of the hepatic portal vein system. On the other hand, a hypophyseal portal system transports blood from the hypothalamus to the anterior pituitary.

Table of Contents

• General Anatomy
• Tributaries of Portal Vein
• Function of Portal Vein
• Frequently Asked Questions – FAQs

General Anatomy

In adults, the portal vein is roughly 8 cm long and has a maximum diameter of 13 mm. It is generated by the joining of the superior mesenteric and splenic veins (the portovenous/portomesenteric confluence) posterior to the pancreas’ neck. The vein’s origin determines the placement of the pancreatic neck.

The portal vein splits into the right and left branches before reaching the liver. It continues to regrow, eventually generating smaller venous branches and portal venules. Every portal venule runs alongside a hepatic arteriole, and the two veins combine to form the portal triad’s vascular components. To supply blood to the liver, these arteries eventually empty into the hepatic sinusoids.

Portacaval Anastomoses

There are various anastomoses between the portal venous system and the systemic venous system. These anastomoses can become inflamed, varicose, or dilated in case of portal hypertension, and eventually rupture.

Auxiliary Hepatic Portal Veins

Auxiliary (Accessory) hepatic portal veins are veins that drain into the liver without connecting to the main hepatic portal vein. The paraumbilical veins (Sappey veins), as well as the veins of the smaller omentum, those draining the gallbladder wall, and the falciform ligament fall into this category.

Tributaries of Portal Vein

The portal vein receives a number of tributaries along its length, including:

• Splenic vein
• Superior mesenteric vein
• Inferior mesenteric vein
• Left and right gastric veins
• Cystic vein

Splenic Vein

The splenic vein (previously the lienal vein) drains blood from the spleen, stomach fundus, and a portion of the pancreas. It’s a part of the portal system for the liver. The portal vein is generated when the splenic vein connects with the superior mesenteric vein.

Superior Mesenteric Vein

The superior mesenteric vein is the blood vessel that discharges blood from the small intestine (jejunum and ileum). It joins the splenic vein beyond the pancreas’ neck to produce the hepatic portal vein. The right gastro-omental vein, veins from the jejunum veins, the ileum, inferior pancreaticoduodenal veins, the middle colic vein, the right colic vein, and the ileocolic vein are its tributaries, which drain the large intestine, small intestine, pancreas, stomach, and appendix.

Inferior Mesenteric Vein

IMV or inferior mesenteric vein is another blood artery in the human anatomy that drains blood from the large intestine. It usually ends when it reaches the splenic vein, which joins the superior mesenteric vein (SMV) to generate the portal vein.

Left and Right Gastric Veins

The left gastric vein (also known as the coronary vein) is a vein that originates from tributaries that drain deoxygenated blood from the stomach’s lesser curvature. It also serves as a channel between the portal vein and the lower esophageal systemic venous system (azygous vein).

The right gastric vein (pyloric vein) discharges deoxygenated blood from the stomach’s lesser curvature into the hepatic portal vein. The right gastric vein connects the stomach to the pylorus via the lesser curvature. It is a component of the portal’s circulatory system.

Cystic Vein

The cystic vein drains the blood from the gallbladder when it is present, and it usually ends in the right branch of the portal vein, along with the cystic duct. It is generally absent, and the blood drains directly to the liver parenchyma via smaller veins in the gallbladder bed.

Function of Portal Vein

The portal vein is responsible for around 75% of the blood flow to the liver. Because the portal vein isn’t a real vein, it doesn’t drain into the heart. Instead, it transports nutrient-rich blood from the gastrointestinal system and spleen to the liver. Before the blood returns to the general circulation, the liver can absorb the nutrients in the blood and filter out any toxic components it contains.

Portal hypertension is a condition in which the blood pressure in the portal vein is abnormally high. The disorder may result in the formation of new blood arteries that bypass the liver, allowing unfiltered blood to circulate throughout the body.

Read Also:

• Hepatic Portal System
• MCQs on Hepatic Portal System