What is this small little green bag in our bodies that can create such a fuss that it sends us running to the ER in the middle of the night? What's it all about, and how can it do that? The gallbladder is a hollow organ like the urinary bladder, but it holds the bile instead of being a receptacle for urine. Since gall is a word for bile, the gallbladder begins to make more sense. The organ is tiny, is generally referred to as pear-shaped (but looks more like an ellipse or thin oval) and it sits snuggled in a depression in the lower right lobe of the liver.
While it is generally covered almost entirely by the liver, it stretches from its normal 2.8 inches to about 4 inches when the gallbladder is full of bile. It often peeps out below the lower margin of the liver. A gallbladder full of stones may also distend below the liver. Its diameter, when full, is only slightly more than an inch and a half. The gallbladder has 3 or 4 parts to it, depending on who you listen to. The three are the fundus, the body, and the neck. The lowest and widest part at the base is called the fundus. The fundus tucks in flat against the abdominal wall, and when it is distended, as when inflamed, it shows up on a CT scan as a bulge, pushing out the abdominal wall. This is called the "tensile gallbladder fundus sign," which is pretty much the only time you'll hear about it. When there is sludge or a few stones, they are usually located in the fundus. The next section is called the body, which is generally narrower unless full of gallstones or bile. Then as it funnels into the neck, some throw in a fourth section and call it the infundibulum, which means "funnel". While the gallbladder color is referred to as green, it is, actually, more of a blue-grey color than green. And when it's diseased, the colors range from rotting flesh color to black, dead, necrotic tissue. Not pretty.
Physiology of the Gallbladder
Let's talk about how the gallbladder works. The liver cells make the bile in the liver. It is then sent through tiny ducts or canals called canaliculi to the duodenum (the first third of the small intestine) and simultaneously to the gallbladder. When foods are ingested (especially proteins and fats), they are mixed with stomach acid and dropped down into the duodenum. Cells in the duodenal walls secrete a hormone called cholecystokinin or CCK, which contracts the gallbladder, and about one-third of its volume is ejected. In turn, CCK signals the relaxation of smooth muscles surrounding the end of the common bile duct called the sphincter of Oddi, allowing the bile to enter the first part of the small intestine. These two muscles, the gallbladder and the Sphincter of Oddi are easily influenced by stress. This is why gallbladder problems often surface after or during times of prolonged stress. CCK is stimulated by fats, amino acids in proteins, or stomach acid, HCl. Not only does CCK stimulate the release of bile but it also increases bile acid production in the liver and digestive enzyme production in the pancreas. Therefore, having sufficient HCl, hydrochloric acid, is important for both bile and pancreatic enzyme production and secretion and therefore for overall digestion. Long-term use of PPIs or other acid blockers can contribute to less efficient digestion.
The Biliary Tree
The gallbladder is part of a whole system called the biliary system or the biliary tree. It is so-called because of its resemblance to a tree, the thousands of tiny branchlets (canaliculi) spreading out throughout the liver, connecting to bigger branches or ducts, then joining two larger liver branches, called hepatic (hepat=liver) ducts, and merging to form the common bile duct or the trunk of the tree. This common bile duct passes through the pancreas and joins with the pancreatic duct before emptying into the duodenum through the common sphincter, the sphincter of Oddi. Farther up the tree, the gallbladder hangs off the common bile duct-like a ripe piece of fruit. The stem of the "fruit" is the cystic duct.