10.11: Gall Bladder

The gallbladder is a sac just under the lower edge of the liver (Figure 10.1). Recall that the gallbladder receives bile from the liver through the cystic duct and that bile in the gallbladder may pass to the small intestine through the common bile duct (Figure 10.8).

The gallbladder stores bile until it is needed for digestion. Recall that bile assists in the digestion and absorption of fat. The gallbladder absorbs water from bile while the bile is being stored.

Emptying of the gallbladder and passage of bile into the small intestine is stimulated by a hormone [cholecystokinin (CCK)] from the small intestine and impulses in parasympathetic nerves. Operation of the CCK control mechanism is especially important when fat enters the small intestine.

Age Changes

Aging causes no significant changes in gallbladder structure. There is a decrease in the sensitivity of the gallbladder to stimulation by CCK. However, with age, the small intestine compensates by producing more CCK. Therefore, contraction of the gallbladder in response to the entrance of fat into the small intestine remains unchanged.

Two age changes associated with the gallbladder involve the bile ducts: The bile ducts widen over most of their length, and the end of the common bile duct near the small intestine becomes narrower. Normally, these changes are not important, but the former one may increase the likelihood that small gallstones formed in the gallbladder will pass down the bile ducts. The latter change inhibits the escape of such stones into the small intestine. As described below, gallstones trapped in the bile ducts can cause cirrhosis and pancreatitis.

Abnormal Changes: Gallstones

Gallstones are solid masses formed from materials in bile (Figure 10.8). They are usually formed in the gallbladder. Gallstones contain various combinations of materials, including cholesterol, bile pigments and salts, calcium, and protein. Many individuals may develop one or a few gallstones. The stones range in size, with some becoming larger than 2 cm in diameter. Some individuals may have 200 or more small stones.

The incidence of gallstones increases with age, and they are fairly common among the elderly. Approximately 25 percent of people over age 50 have gallstones. Gallstones are one of the more common reasons for surgery among older people.

An important cause of gallstone formation is having excessively concentrated bile in the gallbladder, because this situation leads to solidification of materials dissolved in the bile. These circumstances occur more frequently among the elderly because the concentration of bile produced by the liver increases with aging, particularly in obese individuals. In addition, many older persons produce unusually low amounts of cholecystokinin. With less CCK, emptying of the gallbladder is delayed and may be less complete. Since more bile stays in the gallbladder for longer periods, it becomes even more concentrated and bile solidification occurs. Gallstone formation can also be initiated by infections in the gallbladder.

Individuals with gallstones often feel vague discomfort in the abdominal region and the digestive system. Many cases involve severe pain, nausea, and vomiting, especially after one has eaten foods containing fat. The painful attacks are probably caused by contraction of the gallbladder on the gallstones or by movement of a stone into the cystic duct. The gallbladder or bile duct may become injured, inflamed, and infected. In very severe cases it may perforate, spilling bile into the abdominal cavity; this can spread infection and cause a sudden drop in blood pressure.

If a gallstone moves into the bile duct and blocks it, the individual may become jaundiced because bile cannot escape, and bilirubin accumulates in the body. Digestion and absorption of fat are greatly reduced, and malnutrition, including vitamin deficiencies, may develop. If the gallstone lodges below the intersection of the common bile duct and pancreatic duct, pancreatic secretions may be blocked. This can lead to inflammation of the pancreas (pancreatitis), which is discussed below. Prolonged blockage of the bile ducts can cause cirrhosis.

There is no effective way to prevent gallstones, though avoiding obesity reduces the risk of developing them. Gallstones can be removed by several methods, including dissolving them with solutions infused through the bile ducts or with medications, fragmenting them with ultrasound, and extracting them surgically. Surgical removal often includes removal of the gallbladder to prevent a recurrence. A person whose gallbladder has been removed can survive and digest food because the liver can store adequate amounts of bile.