Portal Vein & Bile Duct

PORTAL  VEIN

• It drains the blood from abdominal part of alimentary tract, except lower part of rectum & anal canal.
• It begins like veins from capillary plexus and ends like arteries.
• It acts as reservoir of blood.
• 75% nutrition of liver is provided by portal vein.
• Portal vein & its tributaries are devoid of valves.

FORMATION :-

• It is formed by the union of superior mesenteric & splenic veins behind the neck of pancreas, in front of the inferior vena cava at the level of L2 vertebra.

COURSE  &  RELATIONS :-

• Course of portal vein is divided into extra-hepatic & intra-hepatic parts.

Extra-hepatic  Part 

The trunk of portal vein passes upwards & to the right

runs behind the neck of pancreas & first part of duodenum

enters within the right free margin of lesser omentum in front of epiploic foramen

reaches porta hepatis where it divides into right & left branches

Relations –

• In relation with first part of duodenum course of extra-hepatic part of portal vein is further divided into 3 parts -

Infra-duodenal  Part –

In front- Neck of pancreas

Behind- Inferior vena cava

Right side- Bile duct

Retro-duodenal  Part –

In front-

• First part of duodenum
• Bile duct
• Gastro-duodenal artery

Behind- Inferior vena cava

Supra-duodenal  Part –

In front- (within the lesser omentum)

• Bile duct
• Hepatic artery
• Hepatic plexus of nerves
• Lymphatics

Behind- Inferior vena cava

At the porta hepatis-

• Right & left hepatic ducts
• Right & left branches of hepatic artery
• Right & left branches of portal vein

Intra-hepatic  Part 

• Right & left branches of portal vein supply right & left lobes of liver.
• They are accompanied by branches of hepatic artery & bile ductules.

Right  Branch –

• It is shorter & more vertical
• Receives cystic vein

Left  Branch –

• It is longer & more oblique
• Receives para-umbilical vein
• It is connected with ligamentum teres below & ligamentum venosum above

Portal blood flow in the liver –

Portal vein

Portal  canal

Hepatic sinusoids

Central veins

Sublobular veins

Hepatic veins

Inferior vena cava

TRIBUTARIES :-

1. Superior mesenteric vein
2. Splenic vein
3. Right gastric vein
4. Left gastric vein
5. Cystic vein
6. Paraumbilical vein
   

Occasional  Tributaries 

1. Inferior mesenteric vein
2. Superior pancreatico-duodenal vein
3. Right gastro-epiploic vein
4. Pre-pyloric vein

DEVELOPMENT :-

• The portal vein develops from infra-hepatic part of right & left vitelline veins.
• They pass on each side of the primitive gut & reach the liver.
• Around the primitive duodenum, the vitelline veins are connected to each other by 3 transverse anastomoses - cephalic ventral, middle dorsal & caudal ventral.
• Later splenic vein joins the left side of dorsal anastomosis.
• Therefore, the U-shaped loop of primitive duodenum is encircled by figure of eight anastomosis of these veins.

When the duodenum rotates to the right side, the following changes are observed in the vitelline veins -

• Posterior limb of lower circle of veins disappears & anterior limb persists as superior mesenteric vein.
• Anterior limb of upper venous circle disappears & posterior limb along with the part of right vitelline vein forms the trunk of portal vein.
• Right vitelline vein above the cephalic anastomosis forms the right branch of portal vein.
• Cephalic anastomosis and upper part of left vitelline vein form together left branch of portal vein.

PORTA-CAVAL  ANASTOMOSIS :-

• It is the collateral anastomosis between portal & systemic veins.

Sites  of  Porta-caval  Anastomosis 

1. At the lower end of Oesophagus 

• Left gastric vein  communicates with hemi-azygos vein.

2. At the Ano-rectal junction 

• Superior rectal vein communicates with middle & inferior rectal veins.

3. At the Umbilicus 

• Para-umbilical vein communicates with-
• Superior epigastric & lateral thoracic veins from above
• Superficial epigastric & inferior epigastric veins from below
• Posterior intercostal & lumbar veins on either side.

4. At the Bare area of Liver 

• Portal radicles of liver communicates with diaphragmatic veins.

5. Behind the Peritoneum of Posterior abdominal wall 

• Splenic & colic veins communicate with left renal vein by veins of Retzius.

6. In the Falciform ligament 

• Para-umbilical vein communicates with diaphragmatic veins by accessory portal system of Sappey.

7. At the Fissure for Ligamentum venosum 

• In foetal life, left branch of portal vein communicates with inferior vena cava via ductus venosus.

APPLIED  ASPECTS :-

Portal  Obstruction 

In portal obstruction veins at porta-caval anastomosis get distended & produce –

• Oesophageal varices at the lower end of oesophagus which leads to haematemesis.
• Internal rectal piles at the ano-rectal junction.
• Caput Medusae around the umbilicus like spokes of a wheel.

BILE  DUCT

• It is about 7.5 cm long.
• It is formed close to the porta hepatis by the union of common hepatic and cystic ducts.

Course :-

The bile duct passes downwards, backwards & to the left within the right free margin of lesser omentum, in front of the epiploic foramen

Then it descends behind the first part of duodenum

Lodges in a groove behind the head of pancreas

Reaches the postero-medial wall of second part of duodenum

Here it comes in contact with the main pancreatic duct

Both ducts pierce the duodenal wall separately & unite to form a dilatation known as ampulla of Vater

The ampulla opens on the summit of major duodenal papilla which is situated about 8 – 10cm distal to the pylorus.

• Around the ampulla the duodenal muscles are circularly arranged and form a system of sphincters known as sphincter of Oddi.

Sphincter  of  Oddi :-

It consists of 3 sets of sphincters –

• Sphincter choledochus around the pre-ampullary part of bile duct.
• Sphincter pancreaticus around the pre-ampullary part of pancreatic duct.
• Sphincter of Oddi proper around the termination of ampulla.

Variations in Formation :-

• Cystic duct and common hepatic duct may run parallel to each other united by fibrous tissue and join either behind the first part of duodenum or behind the head of pancreas.
• Cystic duct may pass in front or behind the common hepatic duct and join on its left side.
• An accessory cystic duct may arise above the cystic duct from the common hepatic or right hepatic duct.
• Cystic duct may be absent and the neck of gall bladder directly opens into common hepatic duct.

Variations in Termination :-

• Ampulla may be formed outside the duodenal wall where bile and pancreatic ducts open separately in the ampulla.
• In 30% of individuals ampulla is not formed, where bile and pancreatic ducts open separately on the major duodenal papilla.

Relations :-

Supra-duodenal part (above the first part of duodenum)

• Behind – portal vein
• Left side – trunk of hepatic artery

Retro-duodenal part (behind the first part of duodenum)

• In front – first part of duodenum
• Behind – portal vein
• Left side – gastro-duodenal artery

Infra-duodenal part (below the first part of duodenum)

• In front – head of pancreas, accessory pancreatic duct, anterior row of vasa recta of duodenum
• Behind – posterior row of vas recta, inferior vena cava
• Left side – superior mesenteric and portal veins

Intra-duodenal part (within the second part of duodenum)

• It is about 2 cm in length
• Its course is represented by a longitudinal fold in the interior of the second part of duodenum, which extends upwards from the major duodenal papilla.

Arterial  Supply :-

• Upper part of the duct is supplied by cystic artery.
• Middle part may get small twigs from right hepatic artery.
• Lower part is supplied by posterior superior pancreatico-duodenal artery.

Applied  Aspects :-

• Small gall stones while passing through the bile duct produce stretching pain, which is expressed as biliary colic.
• Sometimes, a gall stone may be imprisoned in the ampulla and produces obstructive jaundice.
• When the bile duct is blocked, the liver is unable to secrete bile due to increased pressure of the duct system.