Anatomy And Physiology

Structure and Function of the Gallbladder



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"Structure and Function of the Gallbladder"
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The gallbladder is a small pear-shaped sac, about three or four inches long by one inch wide, located on the right lobe of the liver. It stores and concentrates bile, a liquid that the body uses to digest fat and neutralize acid. Bile is necessary to digest food, but actually the gallbladder is not. If it must be removed, the bile from the liver will drain directly into the intestines, and digestion will proceed pretty much as it did before.




The gallbladder is composed of three parts. The fondus, the base, sits right on the liver. The neck is the narrow place where the contents of the gallbladder drain into the cystic duct, on the way to the intestine. The main part of the gallbladder, the body, is essentially a muscular sack that holds 20 to 50 milliliters of bile. Bile is a bitter yellow-green liquid composed of cholesterol, bile salts, and bile pigment.




Bile is manufactured in the liver, and collects in the small bile canaliculi. From there it flows into the bile ducts. These drain into the left and right hepatic ducts which either supply the intestines directly or send the bile for storage and concentration in the gallbladder. This many-branched system is referred to as the biliary tree.




The function of the gallbladder is to make the process of digestion run more smoothly in the presence of fat. When someone eats a large amount of it, the intestines signal the gallbladder to secrete extra bile to help with digestion. The hormone that does the signaling is called cholecystokinin, from the Greek words for "move," "sac," and "bile". If the gallbladder has been removed, the body does not have an extra store of concentrated bile to inject all at once to digest a large quantity of fat. But fat in reasonable amounts is perfectly digestible for many people who have had the surgery, especially if it is eaten in combination with other foods.




Surgery, called cholecystectomy, is sometimes necessary for people with painful gallstones. These are most common in women, people over forty, and the obese. Gallstones are crystals that form in bile. If they form in the sac of the gallbladder, they may not even be noticed, or may cause indigestion after eating fatty foods. They can be the size of a grain of rice, or as large as a golf ball, and can form anywhere in the biliary tree. They may become intolerably painful if they lodge in a duct.




Doctors will sometimes use medication, such as ursodeoxycholic
acid, to treat gallstones, though it may have to be taken for years and gallstones may recur when the treatment is stopped. If this is ineffective, they may try lithotripsy. Lithotripsy breaks up stones with well-focused sound waves and the small pieces are then excreted in feces. There may be some pain with this method, both during the procedure (though the patient may be sedated) and during excretion. It is only an option with a small number of gallstones, of relatively small size.




Laparoscopic surgery, done with instruments and a video camera inserted through small incisions in the abdomen is often the preferred method if surgery is needed, because it results in a shorter recovery period. However, in some circumstances, surgery is done through a 5-8 inch incision in the abdomen. Any surgery has risks, but gallbladder removal is a common, well understood, straightforward procedure. After the gallbladder is removed, the bile produced by the liver will drain directly into the intestine, as it did much of the time before the surgery.

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