Portal vein

The whole system is valveless 

• Venous valves help in unidirectional blood flow in veins
• The number of valves is greatest below the knee and decrease in number in the more proximal veins.
• Valveless veins or venous sytem are
• – Inferior vena Cava

– Common iliac veins

– Portal venous system

– Cranial sinuses

All of the above

8-12 mm Hg

In cirrhosis of the liver, portal vein obstruction occur at the level of sinusoids. In cirrhosis there is fibrosis of the liver resulting in architectural distortion with the formation of regenerative nodules. This results in a decrease in hepatocellular mass, its function, and an alteration of blood flow.

Complications of cirrhosis includes portal hypertension and its consequences (such as gastroesophageal variceal hemorrhage, splenomegaly, ascites), hepatic encephalopathy, spontaneous bacterial peritonitis (SBP), hepatorenal syndrome, and hepatocellular carcinoma.

Ref: Harrison’s Internal Medicine, 18th Edition, Page 2598, Chapter 308

Normal portal venous pressure is 5 – 10mmHg (10 – 15cm saline). Portal venous system contributes 75% of blood and 72% of oxygen supplied to the liver. Portal vein is formed by the confluence of superior mesenteric vein and splenic vein. In an average adult 1000-1500ml /min of portal venous blood is supplied to the liver.

Reference:
Schwartz’s Principles of Surgery 9e chapter 31.

Portal hypertension is defined as the elevation of the hepatic venous pressure gradient (HVPG) to >5 mmHg. Portal hypertension is caused by a combination of two simultaneously occurring hemodynamic processes.

Ref: Harrison’s principle of internal medicine 17th edition, chapter 302.

In adults, the portal vein and its tributaries have no valves. In fetal life and for a short postnatal period valves are demonstrable in its tributaries, but they usually atrophy. Rarely some persist in an atrophic form into adulthood.

Portal venous system comprises of portal vein and its 3 tributaries, splenic vein, superior and inferior mesenteric vein. Thses veins drain the blood from the intestinal tract, from the oesophagus to the rectum, from the spleen and pancreas to the liver. Portal vein carries 75% of total blood flow to the liver. Normal portal pressure is 5 – 10mmHg.

The portal venous system is without valves and drains blood from the spleen, pancreas, gall bladder, and abdominal portion of the alimentary tract into the liver. 

The portal vein begins at the level of the second lumbar vertebra and is formed from the convergence of the superior mesenteric and splenic veins. It is 8 cm long and lies anterior to the inferior vena cava and posterior to the neck of the pancreas.

70% of the blood to the liver is carried by portal vein. Hepatic artery carries 30% of the blood to liver. Hepatic artery provides oxygenated blood to the liver and portal vein brings venous blood rich in products of digestion. 

• The hepatic portal vein pass posterior to the first part of duodenum, in the free edge of lesser omentum.
• At the porta hepatis, it divides into right and left branches supplying the right and left lobes of the liver.
• Within the sinusoids of the liver, hepatic portal blood and oxygenated blood from the hepatic artery mix together and come into contact with the hepatocytes, where metabolites such as products of digestion are exchanged.
• Blood from the sinusoids empties into hepatic veins draining the liver and in turn drain into IVC, and blood is returned to heart.

D i.e. The whole system is valveless

Like vena Cava, the portal vein and its tributaries are without valves. The normal pressure in portal vein is 3-5 mmHg and the increase in venous pressure is distributed throughout the splanchenic circulation.

B i.e. Hypophysis cerebri

C i.e. The whole system is valveless

B. i.e. Gall Bladder

B i.e. Portal vein

-Left and right gastric veins drain directly into the portal veinQ.

– Portal vein is formed by union of superior mesenteric & splenic veins behind the neck of pancreas at the level of L₂ vertebrae and runs

upwards with bile duct & hepatic artery (related anteriorly)(2 and inferior i’ena cava (related posteriorly)

B i.e. Halothane

All volatile anesthetic agents reduce portal hepatic blood flow. This decrease is greatest with halothane and least with isofluraneQ.

Ans. is ‘c’ i.e., 5-10 mm Hg 

Answer is C (10-15 cm Saline)

Normal pressure in portal vein is low ’10 – 15 cm saline’ – Harrison 14^th/ 1710.

Normal pressure in portal vein is low ‘5 -10 mm Hg’ – Harrison 16^th/e 1863-

The portal vein drains blood from the abdominal part of the gastrointestinal tract from the lower third of the esophagus to halfway down the anal canal; it also drains blood from the spleen, pancreas, and gallbladder.

The tributaries of the portal vein are the splenic vein, superior mesenteric vein, left gastric vein, right gastric vein, superior pancreaticoduodenal, paraumbilical and cystic veins.

The portal vein enters the liver and breaks up into sinusoids, from which blood passes into the hepatic veins that join the inferior vena cava. The portal vein is about 2 in. (5 cm) long and is formed behind the neck of the pancreas by the union of the superior mesenteric and splenic veins.

Ans. C: 10-12 mm Hg

Normal portal pressure is generally defined between 5 and 10 mm Hg.

Portal hypertension results when the portal pressure rises to 12 mm Hg or greater and complications can arise, such as varices and ascites.

Many conditions are associated with portal hypertension, of which cirrhosis is the most common cause

The portal vein is about 8 cm long.

It is formed by union of superior mesenteric vein and splenic vein behind the neck of pancreas at the level of L₂ vertebrae in front of inferior vena cava (IVC).

Ans. is ‘b’ i.e., Gall bladder

Important relations about portal vein

Infraduodenal part

i) Anterior :- Neck of pancreas

ii) Posterior :- IVC

Retroduodenal part

i) Anterior :- I^stpart of duodenum, bile duct, gastroduodenal artery

ii) Posterior :- IVC

Supraduodenal part

i) Anterior :- Hepatic artery, bile duct

ii) Posterior :- IVC, separated by epiploic formen

Ans. is ‘b’ i.e., Hepatic vein

Histology of the Liver

• Liver is covered by Glisson’s capsule.
• Liver is divided into hexagonal lobules oriented around the terminal tributaries of the hepatic vein (Terminal hepatic veins), i.e. Terminal hepatic vein is in the centre of the lobule and area around the hepatic vein is called centrilobular zone.
• At periphery of lobule, lies the portal tract containing hepatic artery, bile duct and portal vein. Area around portal tract is called periportal zone.
• These three structures (portal vein, hapatic artery and bile duct) form portal triad.
• Area between periportal zone and centrilobular zone is called midzonal area.
• All around the central vein are the major parenchymal cells, i.e. hepatocytes.
• Lobule contains sinusoid (sinusoidal capillaries) which have fenestrated endothelium covering the subendothelial space of Disse. This space contains stellate cell processes and hepatocellular microvilli.
• Other important cells of liver are Kupffer cells, which belong to monocytic-macrophage sytem and function as phagocytic cells.

Ans. is ‘d’ i.e., IVC 

• The portal vein is about 8 cm long. It is formed by the union of the superior mesenteric veins and the splenic vein behind the neck of the pancreas at the level of the second lumbar vertebra. The inferior mesenteric vein drains into the inferior mesenteric vein.

Important facts about portal vein

• 8 cm long
• The blood flow is slow
• Stream line flow :- Blood in superior mesentric vein drains, into right lobe of liver. Blood in splenic and inferior mesentric vein drains into left lobe.
• Relations
• Infraduodenal part

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

• Retroduodenal part

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

• Supraduodenal part

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

• Development of Portal vein :

1. Infra-duodenal part – part of left vitelline vein distal to the dorsal ansatomosis
2. Retro-duodenal part – dorsal anastomosis between two vitelline veins
3. Supra-duodenal part – cranial part of right vitelline vein

• The portal vein receives the following veins :

1. Splenic vein
2. Superior mesenteric vein
3. Left gastric
4. Right gastric
5. Superior pancreatico-duodenal

• Cystic
• Paraumbilical veins

Ans. is ‘b’ i.e., Liver 

• Portal vein is a vein, still it supply blood to liver (usually a vein drains blood from an organ or tissue).

The liver has dual blood supply :-

• 20% of blood supply is through the hepatic artery.
• 80% of blood supply is through the portal vein.