Surgical
anatomy and physiology
The gall bladder is pear-shaped, 7.5—12
cm long, with a normal capacity of about 50 ml, but capable of considerable
distension in certain pathological conditions. The anatomical divisions are a
fundus, a body and a neck that terminates in a narrow infundibulum. The muscle
fibres in the wall of the gall bladder are arranged in a criss-cross manner,
being particularly well developed in its neck. The mucous membrane contains
indentations of the mucosa that sink into the muscle coat; these are the crypts
of Luschka.
The cystic
duct is about 3 cm in length but variable. Its lumen is usually 1—3 mm in
diameter. The mucosa of the cystic duct is arranged in spiral folds known as the
valves of Heister. Its wall is surrounded by a sphincteric structure called the
sphincter of Lutkins. While the cystic duct joins the common hepatic duct in its
supraduodenal segment in 80 per cent of cases, it may extend down into the
retroduodenal or even retropancreatic part of the bile duct before joining.
Occasionally the cystic duct may join the right hepatic duct or even a right
hepatic sectorial duct.
The common
hepatic duct is usually less than 2.5 cm
long and is formed by the union of the right and left hepatic ducts.
The common bile duct is about 7.5
cm long and formed by the junction of the cystic and common hepatic ducts.
It is divided into four parts:
• the supraduodenal
portion, about
2.5 cm long, running in the free edge
of the lesser omentum;
• the retroduodenal portion;
• the infraduodenal portion lies
in a groove, but at times in a tunnel, on the posterior surface of the pancreas;
• the intraduodenal portion passes
obliquely through the wall of the second part of the duodenum where it is surrounded
by the sphincter of Oddi. It terminates by opening on the summit of the papilla
of Vater.
The arterial
supply of the gall bladder is critical. It is proposed that arterial
damage during cholecystectomy may cause ischaemia and result in postoperative
bileduct stricture. The cystic artery, a branch of the right hepatic artery,
is usually given off behind the common hepatic duct (Fig.
54.1). Occasionally,
an accessory cystic artery arises from the gastroduodenal artery. In 15 per cent
of cases the right hepatic artery and/or the cystic artery cross in front of the
common hepatic duct and the cystic duct. The most dangerous anomalies are
where the hepatic artery takes a torturous course on the front of the origin
of the cystic duct, or the right hepatic artery is torturous and the cystic
artery short. The tortuosity is known as the ‘caterpillar turn’ or
‘Moynihan’s hump’ (Fig.54.2).
This
variation is the cause of many problems during a difficult cholecystectomy with
inflammation in the region of the cystic duct. Inadvertent damage to the right
hepatic artery is most difficult to control lap aroscopically.
Lymphatics
The lymphatic vessels of the gall bladder (subserosal and submucosal) drain into the cystic lymph node of Lund (the sentinel lymph node), which lies in the fork created by the junction of the cystic and common hepatic ducts. Efferent vessels from this lymph node go to the hilum of the liver, and to the coeliac lymph nodes. The subserosal lymphatic vessels of the gall bladder also connect with the subcapsular lymph channels of the liver, and this accounts for the frequent spread of carcinoma of the gall bladder to the liver.
Surgical
physiology
Bile, as it leaves the liver, is composed of 97 per cent water, 1—2
per cent bile salts, and 1 per cent pigments, cholesterol and fatty acids. The
liver excretes bile at a rate estimated to be approximately 40 ml/hour. The rate
of bile secretion is controlled by cholecystokinin which is released from the
duodenal mucosa. With feeding there is increased production of bile.
Functions
of the gall bladder
The gall bladder is a reservoir for bile. During fasting resistance to
flow through the sphincter is high, and bile excreted by the liver is diverted
to the gall bladder. After feeding the resistance to flow through the sphincter
of Oddi is reduced, the gall bladder contracts and the bile enters the duodenum.
These motor responses of the biliary tract are in part effected by the hormone
cholecystokinin.
The second main function of the gall bladder
is concentration of bile by active absorption of water, sodium chloride and
bicarbonate by the mucous membrane of the gall bladder. The hepatic bile which
enters the gall bladder becomes concentrated 5—10 times, with a
corresponding increase in the proportion of bile salts, bile pigments,
cholesterol and calcium.
The third function of the gall bladder is the
secretion of mucus — approximately 20 ml is produced per day. With total
obstruction of the cystic duct in a healthy gall bladder, a mucocele develops on
account of this function of the mucosa of the gall bladder.