The liver, gallbladder, pancreas, and spleen are described. The liver is the largest gland and has many functions including bile production, carbohydrate and fat metabolism, and vitamin processing. The gallbladder stores and concentrates bile from the liver. The pancreas produces enzymes and hormones to aid digestion. The spleen filters blood and stores blood cells. All four organs have specific locations, blood supply from the hepatic and splenic arteries, and drainage into the portal vein and lymphatics.