The gallbladder concentrates and stores bile for eventual release into the duodenum. It has a highly folded mucosa that is lined by simple columnar epithelium with an underlying lamina propria. The gallbladder does not have a true submucosa. Rather, it has a muscularis in which the muscle layers are interspersed with connective tissue fibers. An adventitia surrounds the gallbladder where it lies against the liver and a serosa is present where it’s not in contact with other organs. The simple columnar epithelium lining the cavity of the gallbladder is highly specialized for active transport of water, possessing abundant microvilli, mitochondria, and Na+ pumps in its basolateral plasma membranes. These features facilitate the concentration of bile.

Examine the image at the right and these two sections of gall bladder (sample 1, sample 2).

• Identify the major layers (mucosa, muscularis, and adventitia).
• Note the prominent mucosal folds.
• Also note the simple columnar epithelium (SCE) lining the cavity and underlying lamina propria (LP).

Clinical note: A common disorder of the gallbladder is cholelithiasis or the formation of gallstones. These are concretions of cholesterol monohydrate, calcium salts, and phospholipid, which can cause painful inflammation of the gallbladder and/or obstruction of the cystic duct and distention of the gallbladder. Treatment often involves surgical removal of the gallbladder.

Now for the pancreas.