GALL BLADDER

GALL BLADDER

        The gallbladder is a small, pear-shaped, pouch-like organ located in the right upper part of the abdomen. The gall bladder is attached to the inferior surface of liver and is enveloped by liver for a variable portion of its circumference. Sometime gall bladder hangs on a structure called mesentery of gall bladder. The area of attachment of gall bladder to the liver surface is known as “gall bladder fossa”.

Gall bladder is attached with a tubular structure called bile duct which carries the bile from liver to the duodenum (proximal small intestine). Right and left hepatic duct joins together and form common hepatic duct. Once the cystic duct joins with common hepatic duct it continues as common bile duct.

The cystic duct drains the gall bladder into the bile duct. Gall bladder has neck, infundibulum with Hartman’s pouch, body and fundus. The dependent portion of Hartman’s pouch may overlie the common hepatic or right hepatic ducts, thus placing these structures at risk of injury during the performance of laparoscopic cholecystectomy.

      Normally, the cystic duct joins with bile duct in an acute angle on the right side of the common bile duct. The cystic duct can join with bile duct obliquely, left side of bile duct and rarely much lower part of the bile duct. The cystic duct can also join with right hepatic duct, left hepatic duct or confluence of right and left hepatic ducts. Rarely, there can be accessary cystic duct also. The bile duct above the insertion of cystic duct is known as common hepatic duct (CHD) and below the insertion of cystic duct is known as common bile duct (CBD). The length of cystic duct (CD) is about 1 to 5cm. Cystic duct has spiral mucosal folds known as valves of Heister.

The common bile duct has three portions known as supra-duodenal portion, retro-duodenal portion and intrapancreatic portion. The intrapancreatic portion of the common bile duct is regulated by a valve called sphincter of Oddi. The lower part of common bile duct joins with the main pancreatic duct and open at the second part of duodenal mucosa known as ampulla of Vater.

Triangle of Calot:

This is a triangular area bounded by cystic duct below, right hepatic duct medially and inferior border of liver superiorly. The significance of this area is that the cystic artery which supplies the gall bladder arises from right hepatic artery at this triangle.  So, the right hepatic artery is at risk of injury at this triangle during laparoscopic cholecystectomy or open cholecystectomy. There will be a lymph node called Calot’s node (Lund’s lymph node) which will be enlarged in case of any inflammatory pathology of gall bladder or in case of any cancer involving the gall bladder. 

Bile secretion:      

 It is very important to note that bile is produced by the hepatocytes of the liver and not by the gall bladder. The bile has two major roles in human physiology. First, because the liver is a major site of detoxification, bile transport allows excretion of toxins and normal cellular metabolites. Second, bile salts have critical role in absorption of most lipids and fat-soluble vitamins.

       Since the bile increases the absorption of fats, it plays an important role in the absorption of fat and fat-soluble substances including fat soluble vitamins such as the vitamin A, D, E, and K.

        Besides its digestive function, bile also serves as the route of excretion for bilirubin, a by-product of haemoglobin and myoglobin. Bilirubin and its derivatives are transported in the blood bound with albumin is known as unconjugated or indirect bilirubin. This indirect bilirubin is transported into the hepatocyte and in the hepatocytes, they are conjugated with glucuronides to form bilirubin glucuronide known as conjugated or direct bilirubin. 

 Gall bladder is an extrahepatic storage site for bile. Normal storage capacity of gall bladder is about 30 to 60 ml of bile and this bile will be expelled from the gall bladder after taking foods, especially after fatty food

 Bile produced from the liver is concentrated in the gallbladder and discharged from the gall bladder into the duodenum through bile duct depending on the quantity and quality of the food.

     The bile has pigment known as bilirubin derived from the destruction of old red blood cells, bile acids, bile salts, phospholipids, cholesterol, electrolytes and water. Bile salts such as cholic acid and deoxy cholic acid are originally created from cholesterol by the hepatocytes of liver and secreted into the bile canaliculi. The liver actually makes only small amount of total bile salts. After passage into the small intestinal tract and reabsorption by the terminal ileum, bile salts are transported back to the liver for recycling bound to albumin (Enterohepatic circulation). Less than 5% of bile salts are lost each day in the stool. This maintains total bile salt concentration of the body.

The biliary secretion of cholesterol actually serves to excrete cholesterol from the body. Bile is slightly alkaline in nature. 

Although some bile flow is bile salt independent, serving to expel toxins and metabolites from the body, much of the flow is dependent on neural, humoral, and chemical stimuli. Vagal activity induces bile secretion, as does the gastrointestinal hormone secretin.

Cholecystokinin, secreted by the intestinal mucosa, serves to induce biliary tree secretion and gall bladder contraction, thereby augmenting excretion of bile into the intestines. Cholecystokinin, as its name suggests, causes gall bladder contraction, with intraluminal pressure up to 300mmHg.

Vagal activity also induces gall bladder emptying, but is less powerful stimulus to gall bladder contraction than cholecystokinin.

Cholecystokinin contracts the gall bladder and relaxes the sphincter of Oddi. This coordinated mechanism allows for evacuation of up to 70% of gall bladder contents within two hours of cholecystokinin secretion. During the fasting state, the oblique passage of bile duct through the duodenal wall and the tonic activity of sphincter of Oddi prevents duodenal contents from refluxing into the biliary tree. 

Any malfunction or infection involving the gall bladder may leads to gall stone formation which necessitate the removal of gall bladder.

         Bile is not absorbed in to the system properly in case of any intestinal loss or major intestinal disease which leads to inadequate bile acids and bile salts. This inadequate bile salt and acids will end up with bile salt insufficiency and so improper absorption of fat and fat- soluble vitamins.