<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> <P> The lower gastrointestinal tract (GI), includes the small intestine and all of the large intestine . The intestine is also called the bowel or the gut . The lower GI starts at the pyloric sphincter of the stomach and finishes at the anus . The small intestine is subdivided into the duodenum, the jejunum and the ileum . The cecum marks the division between the small and large intestine . The large intestine includes the rectum and anal canal . </P>

Who paved way for the study of digestive system