Ghrelin is a hormone produced primarily in the stomach and small intestine. It is secreted when the stomach is empty, triggering a feeling of hunger. When the stomach is stretched, secretion of ghrelin is inhibited. Leptin is a hormone secreted by adipose cells to signal satiety. Gastrin triggers the secretion of stomach acid during digestion, and cholecystokinin (CKK) is a hormone with various roles in the process of digestion, primarily acting as a hunger suppressant and a trigger for the release of digestive enzymes and bile.

The ileocecal sphincter/valve separates the small intestine from the large intestine. The lower esophageal sphincter, also known as the cardiac sphincter, separates the esophagus from the stomach, while the pyloric sphincter separates the stomach from the small intestine.

The system of coordinated peristaltic waves that slowly sweeps food through the small intestine for digestion is called the migrating motor complex. Disorderly motion of this complex can result in a wide variety of gastrointestinal complaints such as vomiting, dumping syndrome, bloating, or indigestion. Segmentation contractions mix the contents of the colon for more absorption, while mass movements serve to propel feces towards the rectum. 

By the time the contents of the digestive tract ender the colon, the majority of food digestion is complete. The colon then serves primarily to absorb water and electrolytes and to prepare feces for excretion.

The duodenum wraps around the pancreas.

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.