The right and left
liver lobes are drained by the right and left hepatic ducts respectively,
whereas the caudate lobe is drained by several ducts joining both the right and
left hepatic ducts. The intrahepatic ducts are tributaries of the corresponding
hepatic ducts which form part of the major portal tracts invaginating Glisson’s
capsule at the hilus and penetrating the liver parenchyma (Blumgart et
al., 2007).
The left hepatic duct
drains segments (II, III and IV) which constitute the left liver, while the
right hepatic duct drains segments (V, VI, VII, and VIII) that constitute the
right liver. It arises from the junction of two main sectorial ductal tributaries
(anterior V, VIII and posterior VI, VII) (Skandalakis et al., 2004).
The common hepatic duct
is formed by the union of the right and left hepatic ducts in the porta hepatis
at the transverse fissure of the liver. The union of the right and left hepatic
ducts may be intrahepatic or extrahepatic or the common hepatic duct may be
totally absent. Its lower end is defined as its junction with the cystic duct. The
duct is about 1 cm in length, and about 0.4 cm in diameter (Skandalakis
et al., 2004).
The cystic duct
connects the gall bladder to the common hepatic duct to form the common bile
duct. The length of the cystic duct and the manner in which it joins the common
hepatic duct vary, and its diameter is 1-3mm. The cystic duct contains a series
of 5 to 12 crescent shaped folds of mucosa which form the spiral valve of Heister (Skandalakis et
al., 2004).
The
common bile duct begins at the union of the cystic and common hepatic ducts and
ends at the papilla of Vater in the second part of the duodenum. Its length
varies from 5-15 cm, depending on the actual position of the ductal union, and
its diameter is about 6 mm (Newman et al., 1963).
The common bile duct can
be divided into four portions or segments:
1- The
supraduodenal portion, lies between the layers of the hepatoduodenal
ligament in front of the epiploic foramen of Winslow, to the right of the
hepatic artery, and anterior to the portal vein. Its length is 2-5 cm. If the
junction of the cystic and common hepatic ducts is low, the supraduodenal
segment is short or even absent (Lindner et al., 1987).
2- The
retroduodenal portion lies between the superior margin of the first portion
of the duodenum and the superior margin of the head of the pancreas, and the
gastroduodenal artery lies to its left side. It is 1-3.5 cm long. The duct may
be free or partially fixed to the duodenum.
3- The
pancreatic portion extends from the upper margin of the head of the pancreas
to the point of entrance into the duodenum. It passes downward to the right,
posterior to the pancreas or within the pancreatic parenchyma.
4- The
intramural portion takes an oblique course averaging 1.5 cm through the
duodenal wall. Here it receives the main pancreatic duct inferiorly, and the
two ducts usually lie side by side with a common adventitia for several
millimeters. The diameter of both ducts decreases within the duodenal wall. The
septum between the ducts is reduced to a thin mucosal membrane before the ducts
become confluent. They end at the papilla of Vater on the posteromedial wall of
the second part of the duodenum, just to the right of the second or third
lumbar vertebra (Skandalakis et al., 2004).
The gallbladder is 7-10
cm long and has a capacity of 30-50 ml. It is located on the visceral surface
of the liver in a shallow fossa at the plane dividing the right lobe from the
medial segment of the left lobe (the GB-IVC line). The gallbladder is separated
from the liver by the connective tissue of Glisson's capsule. Anteriorly, the
peritoneum of the gallbladder is continuous with that of the liver (Skandalakis
et al., 2004).
The
gallbladder consists of a neck, body, infundibulum and fundus which usually
reaches the free edge of the liver. Large gallstones impacting within the neck
of the gallbladder may create a Hartmann’s pouch. The cystic duct arises from
the neck of the gallbladder and descends to join the common hepatic duct (Wood
1979).
Blood supply of the biliary system
The cystic artery usually arises from the right
hepatic artery as it traverses the hepatocystic triangle to the right of the
common hepatic duct. The lymph node of Calot usually lies superficial to the
position of the cystic artery in the cystic triangle. Reaching the gallbladder
behind the common hepatic duct, the cystic artery usually branches into an
anterior superficial branch and a posterior deep branch. These branches
anastomose and send arterial twigs to the adjacent liver. The cystic artery may
arise from the left hepatic artery or the gastroduodenal artery (Skandalakis
et al., 2004).
The extrahepatic
biliary system receives a rich arterial blood supply, which is divided into
three sections
1- The hilar section receives arterioles
directly from their related hepatic arteries which form a rich plexus with
arterioles from the supraduodenal section.
2- The blood supply of the supraduodenal
section is predominantly axial, most vessels to this section arising from the
retroduodenal artery, the right hepatic artery, the cystic artery, the
gastroduodenal artery and the retroportal artery. Usually, eight small
arteries, each 0.3 mm in diameter, supply the supraduodenal section. The most
important of them run along the lateral borders of the duct and are referred to
as the 3 o’clock and 9 o’clock arteries (Gunji et al., 2006). Of
the arteries supplying the supraduodenal section, 60% run upwards from the
major inferior vessels while 38% run downwards from the right hepatic artery.
Only 2% are non-axial, arising directly from the main trunk of the hepatic
artery as it runs parallel to the bile duct (Staphleton et al., 1998).
3- The retropancreatic section receives
its blood supply from the retroduodenal artery which gives multiple small
branches running around the duct forming mural plexus (Gunji et al.,
2006).
The hepatic surface of
the gallbladder is drained by numerous small veins passing through the
gallbladder bed to the liver. Veins from the hepatic surface drain directly
into the liver. Veins on the free surface open directly or follow the hepatic
ducts into the liver (Skandalakis et al., 2004).
The veins draining the
bile duct mirror the arteries and also drain the gallbladder. This venous
drainage has its own portal venous pathway to the liver parenchyma (Northover
et al., 1979).
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