Gall bladder and biliary system

Introduction of gall bladder

• The gall bladder is a small pouch which is about 4 inch in size, pear shaped sac-like organ and is grey-blue in life.
• It is positioned in a depression under the right lobe of the liver in the upper right section of our abdomen.
• It is made up of an outer serous peritoneal coat, a middle muscular coat and an inner mucous membrane which is continuous with the linings of the ducts.
• Mucin is secreted by the mucous membrane and water is also absorbed readily.
• Bile salts and bile pigments are not absorbed by it, but transports salt out actively, with water following osmotically.
• This is the reason for the concentration of the bile.
• Gallstones might result as the organic constituents of bile leaving the gallbladder is as much as 10 times more concentrated than they were when bile entered from the liver.
• Storage is the main function of gall bladder.
• Bile is secreted by liver continuously in more amount than that required ordinarily.
• The excess bile secreted is stored in gall bladder until needed in the duodenum.
• It can store about 30ml to 60 ml of bile.
• The mucosa of gall bladder is thrown into rugae when it is empty that permits the gallbladder to expand to hold the bile.
• It varies in size, shape and position between different people.
• Rarely, there might be two or even three gallbladders that may work separately by draining into cystic duct, or sharing a common branch that drains into the cystic duct.
• Additionally, the gallbladder may fail to form at all.
• There might also be gallbladders with two lobes separated by a septum.
• These abnormalities are not likely to affect function and are generally asymptomatic.
• Its location in relation to the liver may also vary.
•  Endodermal out-pouching of the embryonic gut tube give rise to gallbladder.

Biliary system

• The biliary system consists of:

1. The gall bladder,
2. The left and right hepatic ducts, that come together as the common hepatic duct,
3. The cystic duct, which extends from the gall bladder, and
4. The common bile duct, which is formed by the union of the common hepatic duct and the cystic duct.

• The common bile duct and the main pancreatic duct join at the entrance to the duodenum about 10 cm from the pyloric orifice.
• They fuse and form the hepato-pancretaic ampulla.
• The ampulla travels obliquely through the duodenal wall and opens in to the duodenum through the duodenal papilla.
• A sphincter located at the outlet of the common bile duct is called the sphincter of the common bile duct (sphincter of Boyden).
• The muscle below it, near the duodenal papilla, is the sphincter of the hepatopancreatic ampulla (sphincter of Oddi).
• Among two sphincters, the sphincter of common bile duct appears to be stronger and more important.
• The sphincter relax, the gall bladder contracts and the bile stored in the gall bladder is squirted into the duodenum whenever chyme enter the duodenum.
• Cholecystokinin is responsible for all the events mentioned above which is one of the hormone released from the small intestine.
• It is released when fatty acids and amino acids reach the duodenum.

Image source: istock

Composition, secretion and functions of bile

• It is an alkaline liquid containing water, sodium bicarbonate, bile salts, bile pigments, cholesterol, mucin, lecithin, and bilirubin.
• About 1 litre of bile is secreted by the liver every day. Its secretion is increased by the chemical, hormonal (secretin) or neural mechanisms.
• It is secreted in needed condition to break down fats or for any of its many other functions.
• Bile salts are cholesterol derivatives which are secreted actively into the bile.
• Then, they eventually pass into the duodenum along with other biliary secretions.
• Bile salts and other biliary secretions recycling takes place between the small intestine and the liver which is called the enterohepatic circulation of these substances.
• Bile color is due to its bile pigments.
• They are derived from the haemoglobin of the worn out red blood cells that are transported to the liver for excretion.
• The color of feces comes from one of the breakdown products of excreted bile pigments.
• The condition called jaundice is due to the excessive amounts of the bile pigment bilirubin in the extra cellular fluids.
• This results in the yellowish coloration of the skin and various other parts of the body.
• The concentrated bile in the gallbladder may form the crystals of cholesterol that are commonly called gallstones.
• Severe pain is noticed if the crystals grow in size blocking the cystic duct thus preventing the flow of bile.

References: 

i) https://www.hopkinsmedicine.org/health/conditions-and-diseases/biliary-system-anatomy-and-functions#:~:text=The%20biliary%20system%20consists%20of,production%20and%20transportation%20of%20bile.

ii) https://www.msdmanuals.com/home/liver-and-gallbladder-disorders/biology-of-the-liver-and-gallbladder/gallbladder-and-biliary-tract

Gall bladder and biliary system