PORTAL VEIN

PORTAL VEIN

• The portal vein or hepatic portal vein is a blood vessel that carries blood from the gastrointestinal tract, common bile duct, pancreas and spleen to the liver.

• Two capillary beds connected by a larger blood vessel characterizes a portal system of blood vessels

• This blood is rich in nutrients that have been extracted from food, and the liver processes these nutrients.

• It also filters toxins that may have been ingested with the food.

• 75% of total liver blood flow is through the portal vein, with the remainder coming from the hepatic artery proper. 

• The blood leaves the liver to reach the heart in the hepatic veins.

• The portal vein is not a true vein, because it conducts blood to capillary beds in the liver and not directly to the heart. 

• It is a major component of the hepatic portal system, one of only two portal venous systems in the body – with the hypophyseal portal system being the other.

• Whole system is valve less.

STRUCTURE:

• 8 cm (3 inches) in adults.

• Originating: behind the neck of the pancreas at L2 level.

• Situated:  deep to the hepatic artery and cystic duct

• Formed by: the union of the superior mesenteric vein and the splenic vein.

• The portal vein is occasionally called the splenic-mesenteric confluence.

• There is stream line flow, i.e blood in superior mesenteric vein drains into right lobe of liver & blood in splenic vein drains into left lobe.

• Before entering the liver thgrough porta hepatis, portal vein divides into right & left bronchus.

• Right branch is shorter & wider, & after receiving cystic vein it enters the right lobe of liver.

Left branch is longer & narrower, & just before entering the left lobe it receives:

– Paraumbilical vein along with ligamentum teres (remnant of left umbilical vein)

– Ligamentum venosum (remnant of ductus venosus)

• It ramifies further, forming smaller venous branches and ultimately portal venules. 

• Each portal venule courses alongside a hepatic arteriole and the two vessels form the vascular components of the portal triad.

• These vessels ultimately empty into the hepatic sinusoids to supply blood to the liver.

Important relations about portal vein

• Portal vein passes behind 1st part of duodenum.

• It can be divided into:

1) Infraduodenal part

• Anterior :- Neck of pancreas

• Posterior :- IVC

2) Retroduodenal part

• Anterior :- Ist part of duodenum, bile duct, gastroduodenal artery

• Posterior :- IVC

  3) Supraduodenal part

• Anterior :- Hepatic artery, bile duct

• Posterior :- IVC, separated by epiploic foramen

TRIBUTARIES:

• Splenic vein

• Superior mesenteric vein

• Inferior mesenteric vein

• Gastric veins

• Cystic & Preumbilical vein

• Superior pancreatico-duodenal

1. Portal hypertension

• Increased blood pressure in the portal vein i.e. elevation of the hepatic venous pressure gradient (HVPG) to >5 mmHg & pressure >10-12mm Hg called portal hypertension, is a major complication of liver disease, most commonly cirrhosis. Normal pressure is 5-10 mm Hg.

• Portal hypertension is caused by a combination of two simultaneously occurring hemodynamic processes.

• Signs of portal hypertension include those of chronic liver disease: ascites, esophageal varices, spider nevi, caput medusae, and palmar erythema.

2. Pylephlebitis

• Pylephlebitis is infection of the portal vein, usually arising from an infectious intraabdominal process such as diverticulosis.

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