EXPLAINING OF GALL BLADDER FUNCTION


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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