<P> The gallbladder is a hollow part of the biliary tract that sits just beneath the liver, with the gallbladder body resting in a small depression . It is a small organ where the bile produced by the liver is stored, before being released into the small intestine . Bile flows from the liver through the bile ducts and into the gall bladder for storage . The bile is released in response to cholecystokinin (CCK) a peptide hormone released from the duodenum . The production of CCK (by endocrine cells of the duodenum) is stimulated by the presence of fat in the duodenum . </P> <P> It is divided into three sections, a fundus, body and neck . The neck tapers and connects to the biliary tract via the cystic duct, which then joins the common hepatic duct to form the common bile duct . At this junction is a mucosal fold called Hartmann's pouch, where gallstones commonly get stuck . The muscular layer of the body is of smooth muscle tissue that helps the gallbladder contract, so that it can discharge its bile into the bile duct . The gallbladder needs to store bile in a natural, semi-liquid form at all times . Hydrogen ions secreted from the inner lining of the gallbladder keep the bile acidic enough to prevent hardening . To dilute the bile, water and electrolytes from the digestion system are added . Also, salts attach themselves to cholesterol molecules in the bile to keep them from crystallising . If there is too much cholesterol or bilirubin in the bile, or if the gallbladder doesn't empty properly the systems can fail . This is how gallstones form when a small piece of calcium gets coated with either cholesterol or bilirubin and the bile crystallises and forms a gallstone . The main purpose of the gallbladder is to store and release bile, or gall . Bile is released into the small intestine in order to help in the digestion of fats by breaking down larger molecules into smaller ones . After the fat is absorbed, the bile is also absorbed and transported back to the liver for reuse . </P> <P> The pancreas is a major organ functioning as an accessory digestive gland in the digestive system . It is both an endocrine gland and an exocrine gland . The endocrine part secretes insulin when the blood sugar becomes high; insulin moves glucose from the blood into the muscles and other tissues for use as energy . The endocrine part releases glucagon when the blood sugar is low; glucagon allows stored sugar to be broken down into glucose by the liver in order to re-balance the sugar levels . The pancreas produces and releases important digestive enzymes in the pancreatic juice that it delivers to the duodenum . The pancreas lies below and at the back of the stomach . It connects to the duodenum via the pancreatic duct which it joins near to the bile duct's connection where both the bile and pancreatic juice can act on the chyme that is released from the stomach into the duodenum . Aqueous pancreatic secretions from pancreatic duct cells contain bicarbonate ions which are alkaline and help with the bile to neutralise the acidic chyme that is churned out by the stomach . </P> <P> The pancreas is also the main source of enzymes for the digestion of fats and proteins . Some of these are released in response to the production of CKK in the duodenum . (The enzymes that digest polysaccharides, by contrast, are primarily produced by the walls of the intestines .) The cells are filled with secretory granules containing the precursor digestive enzymes . The major proteases, the pancreatic enzymes which work on proteins, are trypsinogen and chymotrypsinogen . Elastase is also produced . Smaller amounts of lipase and amylase are secreted . The pancreas also secretes phospholipase A2, lysophospholipase, and cholesterol esterase . The precursor zymogens, are inactive variants of the enzymes; which avoids the onset of pancreatitis caused by autodegradation . Once released in the intestine, the enzyme enteropeptidase present in the intestinal mucosa activates trypsinogen by cleaving it to form trypsin; further cleavage results in chymotripsin . </P>

Which of the following are functions of the digestive system (mark all that apply.)