Gallbladder

The human gallbladder is a hollow grey-blue organ that sits in a shallow depression below the right lobe of the liver. In adults, the gallbladder measures approximately in length and in diameter when fully distended. The gallbladder has a capacity of about . The gallbladder is shaped like a pear, with its tip opening into the cystic duct. The gallbladder is divided into three sections: the fundus, body, and neck. The fundus is the rounded base, angled so that it faces the abdominal wall. The body lies in a depression in the surface of the lower liver. The neck tapers and is continuous with the cystic duct, part of the biliary tree. The gallbladder fossa, against which the fundus and body of the gallbladder lie, is found beneath the junction of hepatic segments IVB and V. The cystic duct unites with the common hepatic duct to become the common bile duct. At the junction of the neck of the gallbladder and the cystic duct, there is an out-pouching of the gallbladder wall forming a mucosal fold known as "Hartmann's pouch". Lymphatic drainage of the gallbladder follows the cystic node, which is located between the cystic duct and the common hepatic duct. Lymphatics from the lower part of the organ drain into lower hepatic lymph nodes. All the lymph finally drains into celiac lymph nodes. Microanatomy of a normal gallbladder wall (H&E stain) The gallbladder wall is composed of a number of layers. The innermost surface of the gallbladder wall is lined by a single layer of columnar cells with a brush border of microvilli, very similar to intestinal absorptive cells. Underneath the epithelium is an underlying lamina propria, a muscular layer, an outer perimuscular layer and serosa. Unlike elsewhere in the intestinal tract, the gallbladder does not have a muscularis mucosae, and the muscular fibres are not arranged in distinct layers. The inner portion of the gallbladder wall (the mucosa) consists of a lining of a single layer of columnar cells which possess small hair-like attachments called microvilli. This sits on a thin layer of connective tissue, the lamina propria. A muscular layer sits beneath the mucosa. This is formed by smooth muscle, with fibres that lie in longitudinal, oblique and transverse directions, and are not arranged in separate layers. The muscle fibres here contract to expel bile from the gallbladder. The muscular layer is surrounded by a layer of connective and fat tissue. The outer layer of the fundus of gallbladder, and the surfaces not in contact with the liver, are covered by a thick serosa, which is exposed to the peritoneum. The serosa contains blood vessels and lymphatics. The location of the gallbladder in relation to the liver may also vary, with documented variants including gallbladders found within, above, on the left side of, behind, and detached or suspended from the liver. Such variants are very rare: from 1886 to 1998, only 110 cases of left-lying liver, or less than one per year, were reported in scientific literature. An anatomical variation can occur, known as a Phrygian cap, which is an innocuous fold in the fundus, named after its resemblance to the Phrygian cap. Development The gallbladder develops from an endodermal outpouching of the embryonic gut tube. ==Function==

The main functions of the gallbladder are to store and concentrate bile, also called gall, needed for the digestion of fats in food. Produced by the liver, bile flows through the biliary tree, consisting of small vessels emptying into the larger hepatic ducts and ultimately the cystic duct, into the gallbladder, where it is stored. At any one time, of bile is stored within the gallbladder. by removal of some water and electrolytes. This is through the active transport of sodium and chloride ions across the epithelium of the gallbladder, which creates an osmotic pressure that also causes water and other electrolytes to be reabsorbed. A function of the gallbladder may involve protection against carcinogenesis as indicated by observations that removal of the gallbladder (cholecystectomy) increases subsequent cancer risk. For instance, a systematic review and meta analysis of eighteen studies concluded that cholecystectomy has a harmful effect on the risk of right-sided colon cancer. Another recent study reported a significantly increased total cancer risk, including increased risk of several different types of cancer, after cholecystectomy. ==Clinical significance==

Gallstones Gallstones form when the bile is saturated, usually with either cholesterol or bilirubin. Most gallstones do not cause symptoms, with stones either remaining in the gallbladder or passed along the biliary system. Gallbladder removal A cholecystectomy is a procedure in which the gallbladder is removed. It may be removed because of recurrent gallstones and is considered an elective procedure. A cholecystectomy may be an open procedure, or a laparoscopic one. In the surgery, the gallbladder is removed from the neck to the fundus, and so bile will drain directly from the liver into the biliary tree. About 30 percent of patients may experience some degree of indigestion following the procedure, although severe complications are much rarer. Complications Biliary injury (bile duct injury) is the traumatic damage of the bile ducts. It is most commonly an iatrogenic complication of cholecystectomy (surgical removal of the gallbladder) but can also be caused by other operations or by major trauma. There is a higher risk of biliary injury during laparoscopic cholecystectomy than during open cholecystectomy. Biliary injury may lead to several complications and may even cause death if not diagnosed in time and managed properly. Ideally, biliary injury should be managed at a center with facilities and expertise in endoscopy, radiology, and surgery. Biloma is an accumulation of bile within the abdominal cavity. It happens when there is a bile leak, for example after surgery for removing the gallbladder (cholecystectomy), with an incidence of . Other causes are biliary surgery, liver biopsy, abdominal trauma, and, rarely, spontaneous perforation. Cancer Cancer of the gallbladder is uncommon and mostly occurs in later life. When cancer occurs, it is mostly of the glands lining the surface of the gallbladder (adenocarcinoma). they are only associated with cancer when large in size (>1 cm). often cause no symptoms and are thus often detected in this way. ==Other animals==

Most vertebrates have gallbladders, but the form and arrangement of the bile ducts may vary considerably. In many species, for example, there are several separate ducts running to the intestine, rather than the single common bile duct found in humans. Several species of mammals (including horses, deer, giraffes, many rodents, and laminoids), several species of birds (such as pigeons and some psittacine species), lampreys and all invertebrates do not have a gallbladder. The bile from several species of bears is used in traditional Chinese medicine; bile bears are kept alive in captivity while their bile is extracted, in an industry characterized by animal cruelty. ==History==

Depictions of the gallbladder and biliary tree are found in Babylonian models found from 2000 BCE, and in ancient Etruscan model from 200 BCE, with models associated with divine worship. Some historians believe the death of Alexander the Great may have been associated with an acute episode of cholecystitis. The first descriptions of gallstones appear to have been in the Renaissance, perhaps because of the low incidence of gallstones in earlier times owing to a diet with more cereals and vegetables and less meat. Anthonius Benevinius in 1506 was the first to draw a connection between symptoms and the presence of gallstones. ==Society and culture==

To have "gall" is associated with bold, belligerent behaviour, whereas to have "bile" is associated with sourness. In traditional Chinese medicine, the gallbladder () is associated with the Wuxing element of wood, in excess its emotion is belligerence and in deficiency cowardice and judgement, in the Chinese language it is related to a multitude of idioms, including using terms such as "a body completely [of] gall" () to describe a forward person, and "single, alone gallbladder hero" () to describe a lone hero, or "they have a lot of gall to talk like that". In the Zangfu theory of Chinese medicine it is an extraordinary Fu or yang organ, as it holds bile. The gallbladder not only has a digestive role, but is seen as the seat of decision-making and judgement. ==See also==