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 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:

1. Paraumblical vein along with ligamentum teres (remnant of left umblical vein)
2. 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

1. Anterior :- Neck of pancreas
2. Posterior :- IVC

2. Retroduodenal part

1. Anterior :- Ist part of duodenum, bile duct, gastroduodenal artery
2. Posterior :- IVC

3. Supraduodenal part

1. Anterior :- Hepatic artery, bile duct
2. Posterior :- IVC, separated by epiploic formen

TRIBUTARIES:

• Splenic vein
• Superior mesenteric vein
• Inferior mesenteric vein
• Gastric veins
• Cystic & Preumblical 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.