EXPLAINING OF GALL BLADDER FUNCTION

Introduction

The gall bladder is that organ which present in under surface of the liver and has pear shaped sac which divided into four parts from above downward fundus body infundibulum and the neck

The gall bladder contain inside it a fluid called bile which it is secreted from the liver and stored into the gall bladder the average capacity of the gall bladder to store bile from 30-50 ml which can be reach up to 300 ml in case of gall bladder obstruction

The liver secreted about 500-1000 ml of bile per day this secretion depend on several factors which either increase or decrease secretion of the bile these factors are neuroginc humoral and chemical stimuli

The bile consists of water electrolytes bile salts proteins lipids and bile pigment

The bile salts are cholate and chenodeoxy cholate which are synthesized in the liver from cholesterol

The bile acids when the bile salts conjugated with taurine and glycine they called bile acids

The gallbladder,together with the bile ducts, and the sphincter of Oddi acts to store and regulate the fow of bile

The sphincter of Oddi regulates flow of bile (and pancreatic juice) into the duodenum and prevents the regurgitation of duodenal contents into the biliary tree, and diverts bile into the gallbladder

The main function of the gallbladder is to concentrate and store hepatic or liver bile and to transfer bile into the duodenum to reach the intestine and which is a part reabsorpted through enterohepatic circulation (entro) mean intestine and (hepatic) mean liver and part excreted into the stool and urine in response to meal

The function of gall bladder can be divided into

Absorption and Secretion

During people fasting about more than two third of the bile secreted by the liver is stored in the gallbladder

The gallbladder mucosa has a wide absorptive capacity as It rapidly absorbs sodium, chloride, and water and concentrating the bile and leading to a marked change in bile composition. This rapid absorption is one of the mechanisms that prevent a rise in pressure within the biliary system under normal circumstances

The epithelial cells of the gallbladder secrete two important substance into the gallbladder lumen

glycoproteins and hydrogen ions

The mucosal glands in the infundibulum and the neck of the gallbladder secrete mucus glycoproteins

Which protect the mucosa from the erosion (lytic) action of bile and to facilitate the passage of bile through the cystic duct

This mucus makes up the colorless white bile seen in gall bladder dilatation (hydrops ) resulting from cystic duct obstruction

The transport of hydrogen ions by the gallbladder epithelium leads to a decrease in the gallbladder bile pH

The acidification promotes calcium solubility, thereby preventing its precipitation as calcium salts.

Motor Activity

Gallbladder filling is facilitated by tonic contraction of the sphincter of Oddi, which creates a pressure gradient between the bile ducts and the gallbladder

During fasting the gallbladder does not simply fill passively

repeatedly empties small volumes of bile into the duodenum is mediated by the hormone motilin

In response to a meal, the gallbladder empties by a coordinated gallbladder contraction and sphincter of Oddi relaxation

One of the main stimuli to gallbladder emptying is the hormone cholecystokinin CCK

CCK is released endogenously from the duodenal mucosa in response to a meal

When stimulated by eating, the gallbladder empties 50 to 70% of its contents within 30 to 40 minutes

Over the following 60 to 90 minutes the gallbladder gradually refills

Other hormonal and neural pathways also are involved in the coordinated action of the gallbladder and the sphincter of Oddi

Any abnormalities in this function play a role in cholesterol nucleation and gallstone formation

Neurohormonal Regulation

Nerve regulation

The vagus nerve stimulates contraction of the gallbladder, and splanchnic sympathetic stimulation is inhibitory to its motor activity

Parasympathomimetic drugs contract the gallbladder, whereas atropine leads to relaxation

Neurally mediated reflexes link the sphincter of Oddi with the gallbladder, stomach, and duodenum to coordinate the flow of bile into the duodenum

Distention of Antrum of the stomach causes contraction of gallbladder and relaxation of the sphincter of Oddi

Hormonal regulation

Hormonal receptors are found on the smooth muscles, vessels, nerves, and epithelium of the gallbladder

CCK is a peptide that comes from epithelial cells of the upper gastrointestinal tract and is found in the highest concentrations in the duodenum

CCK is released into the blood stream by acid, fat, and amino acids in the duodenum

CCK acts directly on smooth muscle receptors of the gallbladder and stimulates gallbladder contraction

It also relaxes the terminal bile duct, the sphincter of Oddi, and the duodenum

CCK stimulation of the gallbladder and the biliary tree also is mediated by cholinergic vagal neurons

In patients who have had a vagotomy, the response to CCK stimulation is decreased and the size and the volume of the gall bladder are increased

VIP hormones inhibits contraction and causes gallbladder relaxation

Somatostatin hormones and its analogues are potent inhibitors of gallbladder contraction

Patients treated with somatostatin analogues and those with somatostatinoma have a high incidence of gallstones, due to the inhibition of gallbladder contraction and emptying

Other hormones such as substance P and enkephalin affect gallbladder motility

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