The portions of the small intestine, in order from superior to inferior, are the duodenum, the jejunum, and the ileum. The cecum is not a part of the small intestine at all but rather the beginning of the large intestine.

The pudendal nerve innervates the external anal sphincter and is responsible for a person's ability to voluntarily control defecation. Dysfunction of the pudendal nerve has been associated with fecal incontinence or constipation. The other nerves listed are all part of the pelvic floor but do not directly innervate the anal sphincter.

The majority of absorption of nutrients in the small intestine occurs mainly in duodenum and the jejunum. The ileum is still a site of some absorption, though it is far less than nutrient absorption in the superior parts of the small intestine. The cecum is part of the large intestine.

The hepatic portal vein is the main vein the carries nutrient-rich blood from the digestive tract to the liver for further processing. The other veins listed are all smaller veins that drain the stomach, small intestine, and spleen into the portal vein. 

The muscular sphincter that keeps stomach contents from regurgitating into the esophagus is the lower esophageal sphincter. The upper esophageal sphincter separates the esophagus from the pharynx, the pyloric sphincter separates the stomach from the small intestine, and the ileocecal valve separates the small intestine from the large intestine.

The areas of the stomach, from superior to inferior, are the fundus, the body, and the pyloric antrum. The rugae are folds in the stomach that increase its surface area and expandability. 

The ligament of Treitz suspends the duodenum, while the splenorenal ligament goes between the left kidney and the spleen. Ligamentum flava are ligaments present in the spinal cord.

Amylase enzymes, produced by the salivary gland and the pancreas, break starched down into simple sugars. Peptidase and protease enzymes break down proteins, while lipase enzymes break down lipids.

Bile acids, produced in the liver and stored in the gallbladder, help emulsify fats during digestion. The process of emulsification makes fats collect into small droplets, increasing the surface area of ingested lipids and increasing the ability of pancreatic lipase to break fats down into fatty acids and glycerol. Hydrochloric acid aids in the breakdown of proteins in the stomach, and cholecystokinin is a hormone with a wide variety of functions in the digestive process, including the stimulation of the release of bile (though it does itself not play a role in emulsification of fats).

Normal gastric pH ranges from 1.5 to 3.5. This highly acidic environment aids the stomach in denaturing proteins, a fundamental part of digestion.