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.
- The biliary system consists of:
- The gall bladder,
- The left and right hepatic ducts, that come together as the common hepatic duct,
- The cystic duct, which extends from the gall bladder, and
- 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.
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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.
Gall bladder and biliary system