Gastrointestinal Physiology - NCLEX-PN

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 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 duodenum wraps around the pancreas.

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 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 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 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.

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.

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.

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.

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.

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

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.

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.