Portal Vein

INTRODUCTION:
  • 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:
  • Measuring approximately 8 cm (3 inches) in adults, the portal vein is located in the right upper quadrant of the abdomen, originating behind the neck of the pancreas at L2 level
  • Situated deep to the hepatic artery and cystic duct
  • In most individuals, the portal vein is formed by the union of the superior mesenteric vein and the splenic vein.For this reason, the portal vein is occasionally called the splenic-mesenteric confluence.
  • Occasionally, the portal vein also directly communicates with the inferior mesenteric vein, although this is highly variable.
  • Other tributaries of the portal vein include the cystic and gastric veins.
  • Immediately before reaching the liver, the portal vein divides into right and left.
  • 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.
Portacaval anastomoses
  • The portal venous system has several anastomoses with the systemic venous system.
  • In cases of portal hypertension these anastamoses may become engorged, dilated, or varicosed and subsequently rupture.
Accessory hepatic portal veins
  1. Accessory hepatic portal veins are those veins that drain directly into the liver without joining the hepatic portal vein.
  2. These include the paraumbilical veins as well as veins of the lesser omentum, falciform ligament, and those draining the gallbladder wall.
  3. Important relations about portal vein
  • Infraduodenal part
  1. Anterior :- Neck of pancreas
  2. Posterior :- IVC
  • Retroduodenal part
  1. Anterior :- Istpart of duodenum, bile duct, gastroduodenal artery
  2. Posterior :- IVC
  • 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 vein
FUNCTIONS:
  • The portal vein and hepatic arteries form the liver's dual blood supply.
  • Approximately 75% of hepatic blood flow is derived from the portal vein, while the remainder is from the hepatic arteries.
  • Unlike most veins, the portal vein does not drain into the heart. Rather, it is part of a portal venous system that delivers venous blood into another capillary system, the hepatic sinusoids of the liver.
  • In carrying venous blood from the gastrointestinal tract to the liver, the portal vein accomplishes two tasks: it supplies the liver with metabolic substrates and it ensures that substances ingested are first processed by the liver before reaching the systemic circulation. This accomplishes two things.
  1. Possible toxins that may be ingested can be detoxified by the hepatocytes before they are released into the systemic circulation.
  2. The liver is the first organ to absorb nutrients just taken in by the intestines. After draining into the liver sinusoids, blood from the liver is drained by the hepatic vein. 
CLINICAL SIGNIFICANCE:
  • Portal hypertension
  1. 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 is5-10 mm Hg.
  2. Portal hypertension is caused by a combination of two simultaneously occurring hemodynamic processes.
  3. 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.
Exam Question
  • Portal Vein is formed by the union of superior mesenteric vein and the splenic vein.
  • The whole hepatic portal system is valveless
  • The Normal Portal venous pressure is 5-10mm Hg
  • Portal hypertension is defined as the elevation of the hepatic venous pressure gradient (HVPG) to >5 mmHg.
  • Left gastric vein drains into portal vein
  • Portal vein begins at L2 level
  • Two capillary beds connected by a larger blood vessel characterizes a portal system of blood vessels
  • Portal vein provides maximum blood supply to liver.
  • Portal vein is Situated deep to the hepatic artery and cystic duct
  • Portal circulation is also seen in an endocrine gland i.e. hypophysis cerebri
  • Portal vein is related to Pancreas,Inf. vena cava,CBD, GIT, Spleen, Liver
  • Veins draining into portal vein are Splenic vein, Superior mesenteric vein, Inferior mesenteric vein, Gastric veins, Cystic vein
  • Portal hypertension is said to be present if portal venous pressure is more than 10-12mm Hg
  • Portal triad in liver is formed by Hepatic artery, Bile duct, Portal vein
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