Structure and function of accessory organ-3

The Biliary Tract and the Gallbladder

The biliary tree is a network of passageways that transports bile from the liver, where it is produced, and the gall bladder, where it is temporarily stored, to the gut (site of action of bile). The bile canaliculi in the liver lobules are where the biliary apparatus starts. All of the bile from each liver lobe is eventually gathered in a single big duct after joining to form the interlobular bile ducts. The common hepatic duct is created when the right and left hepatic ducts combine. Together, these and the gall bladder's cystic duct form the common bile ducts. The main pancreatic duct and the CBD typically join just before the bile is emptied into the duodenum at the vater's ampulla through the sphincter of Oddi.

The bile that the liver produces travels through the biliary system and into the duodenum. The sphincter of Oddi closes when bile is not required for digestion, allowing bile to fill the CBD and collect in the gall bladder. By collecting water and ions, the gall bladder concentrates the bile before storing it for later release. The intestinal hormone cholecystokinin (CCK), which induces contraction of the gall bladder wall and relaxation of the sphincter of Oddi, as well as the presence of fat and acid chyme and cholecystokinin in the duodenum, trigger the release of stored bile.

The Gall Bladder

The gallbladder is a greenish, pear-shaped muscular sac that stores bile and is connected by connective tissue to the back of the liver. It has a neck, a body, which is its fundamental component. Normally, its head (fundus), which is located at the tip of the ninth costal cartilage in the midclavicular line, extends slightly beyond the inferior edge of the liver. Its neck continues into the common bile duct from the cystic duct. Bile can be found in the gall bladder in amounts of 30 to 60 ml (on average 50 ml). The ducts of the biliary tree and the gall bladder have the same layers of tissues as those described in the general alimentary tract layout. Gall bladder mucosa is composed of straightforward columnar epithelium.

Blood Supply of the Gall bladder

The cystic artery, a branch of the hepatic artery, provides the gall bladder with arterial blood. The cystic vein, which connects to the portal vein, drains the venous blood.

Nerve Supply of the Gall bladder

The gall bladder is supplied by sympathetic and parasympathetic nerve fibers.

Function of the Gallbladder

• It serves as a bile reserve.
• Through the gall bladder mucosa's absorption of water and ions, the gall bladder can concentrate bile up to 10 or 15 times.
• When required, it lets the stored bile out.

Bile

Hepatocytes secrete bile, 500 to 1000 ml of which are done so each day. It is a fluid that is greenish-yellow in color and contains phospholipids, cholesterol, neutral fats, bile salts, minerals, and bile pigments. Old RBCs are broken down into hemoglobin, which is then used to make bilirubin, the main bile pigment. The bacteria in the intestine convert bilirubin to stercobilim, which gives feces their characteristic brown color. Feces appear grayish white when there is no bile secretion, and this indicates that there is an obstruction in the biliary tract.

Steroid substances called bile salts are made of cholesterol. The only function of the liver in digestion is the release of bile salts and phospholipids, which aid in the digestion and absorption of dietary fat. The bile's other components are all wastes that should be expelled. These waste products collect when bile is overly concentrated and may result in gall stones.

In contrast to other bile components, bile salts are mostly reabsorbed in the ileum, transported back to the liver via the hepatic portal blood, and then resecreted. The enterohepatic circulation refers to this route from the liver to the ileum and back to the liver.

Composition of the bile

97-98% of it is water, and 2% to 3% of it is solid. The solids consist of:

• Bile salts, bile pigments, cholesterol, fatty acids, lecithin, and mucus are examples of organic solids.
• Sodium, calcium, potassium, bicarbonate, and chloride are examples of inorganic solids.