Gallbladders
Essay title: Gallbladders
Gallbladders
I decided to write my paper on the gallbladder, because I find this particular organ interesting. There will be some information about bile, a substances the liver manufactures and the gallbladder stores. This paper will elaborate on the structure and functions of the gallbladder. There is an explanation of the gallbladders emptying process, and the chemicals that aide in its engagement. Also included is information on disorders of the gallbladder and diseases of the gallbladder. I will discuss the different types of gallstones involved in gallbladder disorders, also the different kinds of diseases of the gallbladder.
The Liver produces a substance called bile, which is used to help in the digestion of fatty foods. The bile is secreted from liver cells into small bile ducts, which join together to form the common hepatic duct. The bile then goes into the gallbladder where it is stored and concentrated for later use.
The Gallbladder is a muscular organ that serves as a container for bile, present in most vertebrates. In humans, it is a pear-shaped membranous sac on the undersurface of the right lobe of the liver just below the lower ribs. It is usually about 3 inches long and 1 inch in diameter at its thickest part; it has a capability varying from 1 to 1.5 fluid ounces. The body (corpus) and neck (collum) of the gallbladder extend backward, upward and to the left. The wide end (fundus) leans downward and forward, sometimes extending slightly beyond the edge of the liver. “Structurally, the gallbladder consists of an outer peritoneal coat (tunica serosa); a middle coat of fibrous tissue and unstriped muscle (tunica muscularis); and an inner mucous membrane coat (tunica mucosa”). (Tortora,1993,pp.413).
The functions of the gallbladder are to store and concentrate bile (up to 10 fold) until it is needed in the small intestine. In the concentration method, water and ions are absorbed by the mucosa of the gallbladder.
Emptying of the gallbladder is the role of Cholecystokinin. When food begins to be digested in the upper intestinal tract, the gallbladder begins to empty, especially as fatty foods enter the duodenum about 30 minutes after a meal. The gallbladder contracts and forces bile into the cystic duct, through the common bile duct and into the small intestine. The key cause of the emptying is rhythmical contractions of the wall of the gallbladder, but effective emptying also requires simultaneous relaxation of the sphincter of oddi that protects the exist of the common bile duct to the duodenum.
By far the most potent stimulus for causing the gallbladder contractions is the hormone cholecystokinin. This is the same cholecystokinin that causes increased secretion of enzymes by the acinar cells of the pancreas. The stimulus for its release into the blood from the duodenal mucosa is mainly the fatty foods themselves that enter the duodenum.
“In addition to Cholecystokinin, the gallbladder is stimulated less strongly by Acetycholine- secreting nerve fibers from both the Vagi and the Enteric Nervous System. They are the same nerves that promote motility and secretion in other parts of the upper gastrointestinal tract.”(Guyton, 1994,pp.827-828).
Even with moderately strong contractions of the gallbladder, emptying can be difficult because the sphincter of oddi generally remains strongly contracted. Therefore, before emptying of the gallbladder occurs; the sphincter of oddi, too, must be relaxed. At least three factors help in this: First, cholecystokinin, instead of stimulating the sphincter of oddi has a relaxing effect, but this effect is usually not enough alone to allow significant emptying. Second, the rhythmical contractions of the gallbladder transmit peristaltic waves down the common bile duct to the sphincter of oddi, causing a leading wave of relaxation that to some extent inhibits the sphincter in advance of the peristaltic wave. But this too, is usually not enough to allow large amounts of emptying. Third, when intestinal peristaltic waves move over the wall of the duodenum itself, the relaxation phase of each of these waves strongly relaxes the sphincter of oddi along with the relaxation of the muscle of the gut wall. This seems to be by far the most effective of all the relaxant effects on the sphincter of oddi. As a result, bile usually enters the duodenum in the form of squirts that are coordinated with the relaxation phase of the duodenal peristaltic waves.
In summary, the gallbladder empties its store of concentrated bile into the duodenum mainly in response to the Cholecystokinin stimulus. When fat is not in the meal, the gallbladder empties poorly, but when ample quantities of fat are present, the gallbladder normally empties completely in about 1 hour.
Bile