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Gallstones can occur anywhere within the biliary tree, including the gallbladder and the common bile duct. Obstruction of the common bile duct is choledocholithiasis; obstruction of the biliary tree can cause jaundice; obstruction of the outlet of the pancreatic exocrine system can cause pancreatitis. Cholelithiasis is the presence of stones in the gallbladder or bile ducts: chole- means "bile", lithia means "stone", and -sis means "process".
A gallstone's size can vary and may be as small as a sand grain or as large as a golf ball. The gallbladder may develop a single, often large stone or many smaller ones. They may occur in any part of the biliary system.
Gallstones have different appearance, depending on their contents. On the basis of their contents, gallstones can be subdivided into the two following types:
The proportions of these different types of stone found varies between samples, and is thought to be affected by the age and ethnic or regional origin of the patients. 
All stones are of mixed content to some extent. Those classified as mixed, however, contain between 30% and 70% of cholesterol. In most cases the other majority constituent is calcium salts such as calcium carbonate, palmitate phosphate, and/or bilirubinate. Because of their calcium content, they can often be visualized radiographically
Also know as "Fake stones," they are sludge-like gallbladder secretions that act like a stone.
Researchers believe that gallstones may be caused by a combination of factors, including inherited body chemistry, body weight, gallbladder motility (movement), and perhaps diet.
Cholesterol gallstones develop when bile contains too much cholesterol and not enough bile salts. Besides a high concentration of cholesterol, two other factors seem to be important in causing gallstones. The first is how often and how well the gallbladder contracts; incomplete and infrequent emptying of the gallbladder may cause the bile to become overconcentrated and contribute to gallstone formation. The second factor is the presence of proteins in the liver and bile that either promote or inhibit cholesterol crystallization into gallstones.
In addition, increased levels of the hormone estrogen as a result of pregnancy, hormone therapy, or the use of combined (estrogen-containing) forms of hormonal contraception, may increase cholesterol levels in bile and also decrease gallbladder movement, resulting in gallstone formation.
No clear relationship has been proven between diet and gallstone formation. However, low-fibre, high-cholesterol diets, and diets high in starchy foods have been suggested as contributing to gallstone formation. Other nutritional factors that may increase risk of gallstones include rapid weight loss, constipation, eating fewer meals per day, eating less fish, and low intakes of the nutrients folate, magnesium, calcium, and vitamin C. On the other hand, wine and whole grain bread may decrease the risk of gallstones.
The common mnemonic for gallstone risk factors refer to the "four F's": fat (i.e., overweight), forty (an age near or above 40), female, and fertile (pre-menopausal); a fifth F, fair is sometimes added to indicate that the condition is more prevalent in Caucasians. The absence of these risk factors does not, however, preclude the formation of gallstones.
Interestingly, a lack of melatonin could significantly contribute to gallbladder stones, as melatonin both inhibits cholesterol secretion from the gallbladder, enhances the conversion of cholesterol to bile, and is an antioxidant, capable of reducing oxidative stress to the gallbladder.
Gallstones usually remain asymptomatic initially. They start developing symptoms once the stones reach a certain size (>8 mm). A main symptom of gallstones is commonly referred to as a gallstone "attack", also known as biliary colic, in which a person will experience intense pain in the upper abdominal region that steadily increases for approximately thirty minutes to several hours. A patient may also experience pain in the back, ordinarily between the shoulder blades, or pain under the right shoulder. In some cases, the pain develops in the lower region of the abdomen, nearer to the pelvis, but this is less common. Nausea and vomiting may occur. Patients characteristically exhibit a positive Murphy's sign: the patient is instructed to breathe in while the gall bladder is deeply palpated. If the gallbladder is inflamed, the patient will abruptly stop inhaling due to the pain, a positive Murphy's sign.
These attacks are sharp and intensely painful, similar to that of a kidney stone attack. Often, attacks occur after a particularly fatty meal and almost always happen at night. Other symptoms include abdominal bloating, intolerance of fatty foods, belching, gas, and indigestion. The patient should also make sure they're drinking an appropriate amount of water relative to the number of calories being taken in. If the above symptoms coincide with chills, lowgrade fever, yellowing of the skin or eyes, and/or clay-colored stool, a doctor should be consulted immediately.
Some people who have gallstones are asymptomatic and do not feel any pain or discomfort. These gallstones are called "silent stones" and do not affect the gallbladder or other internal organs. They do not need treatment.
Cholesterol gallstones can sometimes be dissolved by oral ursodeoxycholic acid, but it may be required that the patient takes this medication for up to two years. Gallstones may recur however, once the drug is stopped. Obstruction of the common bile duct with gallstones can sometimes be relieved by endoscopic retrograde sphincterotomy (ERS) following endoscopic retrograde cholangiopancreatography (ERCP). Gallstones can be broken up using a procedure called lithotripsy (Extracorporeal Shock Wave Lithotripsy), which is a method of concentrating ultrasonic shock waves onto the stones to break them into tiny pieces. They are then passed safely in the feces. However, this form of treatment is only suitable when there are a small number of gallstones.
Cholecystectomy (gallbladder removal) has a 99% chance of eliminating the recurrence of cholelithiasis. Only symptomatic patients must be indicated to surgery. The lack of a gall bladder does not seem to have any negative consequences in many people. However, there is a significant portion of the population — between 5 and 40% — who develop a condition called postcholecystectomy syndrome which may cause gastrointestinal distress and persistent pain in the upper right abdomen. In addition, as many as 20% of patients develop chronic diarrhea.
There are two surgical options for cholecystectomy:
Gallstones are a valuable by-product of meat processing, fetching up to US$32–per–gram in their use as a purported antipyretic and antidote in the folk remedies of some cultures, particularly in China. The finest gallstones tend to be sourced from old dairy cows, which are called Niu-Huang (牛黄，yellow thing of oxen) in Chinese. Those obtained from dogs, called Gou-Bao (狗宝，treasure of dogs) in Chinese, are also used today. Much as in the manner of diamond mines, slaughterhouses carefully scrutinize offal department workers for gallstone theft.