While a small amount of fat digestion may occur in the mouth via the action of lingual lipase, the majority of lipid digestions begins in the duodenum. The presence of fat in the small intestine triggers release of pancreatic lipase, which enters the duodenum via the pancreatic duct. Fat digestion does not occur in the stomach.

The pancreatic duct and common bile duct come together at the ampulla of vater, allowing for the combination of pancreatic enzymes and bile. This combination is released into the duodenum via the relaxation of the sphincter of Oddi, a muscular ring at the end of the ampulla. The sphincter of Oddi also prevents any back-flow of duodenal contents into the ampulla.

The pyloric sphincter controls flow of chyme between the stomach and the duodenum, while the ileocecal valve separates the small and large intestine. 

Lipids are transported out of the digestive system via lacteals, lymphatic capillaries within the vilii of the small intestine that absorb fatty acids in the form of chylomicrons. They are then transported through the lymphatic system and re-enter the blood stream via the thoracic duct.

The hepatic system produces bile, a vital part of lipid digestion, but it does not absorb lipids. Nor does the excretory system, which is not really a single system but rather a collection of organ systems including the kidney, skin, liver, and colon.

Gastrin is produced by the G cells of the stomach. Parietal cells of the stomach secrete hydrochloric acid, while chief cells secrete pepsinogen and chymosin. Beta-islet cells of the pancreas produce glucagon. 

The hydrolysis of oligosaccharides into disaccharides occurs in the duodenum, after the addition of pancreatic amylase from the pancreatic duct.   

Gastrin, a peptide hormone released by G-cells of the stomach, has many functions in digestion. It triggers parietal cells to release , it increases gastric motility, it triggers chief cells to secrete pepsinogen, and it stimulates the gallbladder to release bile. 

The intestinal brush border is the microvilli-covered surface of the small intestine. It is where a large part of the digestive process occurs, aided by brush-border enzymes such as sucrase, maltase, lactase, and carboxypeptidase. 

Insulin, while secreted by the pancreas, is not an enzyme. Rather it is a peptide hormone that plays a role in lipid and blood sugar metabolism.

The other enzymes listed are all pancreatic enzymes that play a role in digestion. Amylase breaks down carbohydrates, while lipase and sterol esterase break down fats. Carboxypeptidase is an enzyme that removes the final amino acid group from a protein.

 is secreted by parietal cells of the stomach. Chief and foveolar cells of the stomach secrete pepsinogen and mucus respectively, and M cells are not stomach cells, but rather intestinal cells involved in mucosa-associated lymphoid tissues, or MALT. 

The two main forms of digestion and chemical and mechanical. Mechanical digestion involves the physical crushing, mixing, and breaking down of food particles into small pieces or slurries. Mechanical digestion primarily occurs with mastication and is carried out to some degree by peristaltic contractions of the stomach and intestine. Chemical digestion is the further breakdown of food particles into their molecular parts. This is carried out primarily via enzymes, HCl, and bile.