The gastrointestinal, or GI, tract produces and secretes a wide array of peptides that act as hormones, coordinating and regulating the activities of the digestive system. The cells that secrete GI hormones reside within the lining of the digestive tract, enabling detection of the changing environment. The interplay of the GI tract peptides proves essential for normal digestion and absorption of food nutrients.
Gastrin
G-cells of the stomach produce the peptide gastrin, which controls stomach acid secretion. Ingestion of protein and its building blocks, amino acids, serve as the principal stimulation for gastrin secretion. Beer, wine and coffee also act as strong stimulants of gastrin secretion, notes the online pathophysiology text of Colorado State University. Gastrin binds to the parietal cells of the stomach lining, stimulating production and secretion of digestive acid. After the stomach empties, gastrin secretion stops, halting acid release.
Secretin
Secretin is a GI peptide produced by the first part of the small intestine, the duodenum. Passage of acidic stomach contents into the duodenum stimulates the release of secretin, which in turn stimulates the flow of digestive fluids from the pancreas. The digestive fluids from the pancreas contain enzymes that break down proteins, fats and sugars. The fluid also contains high concentrations of bicarbonate, which neutralizes stomach acid. Once the acidic stomach contents pass through the duodenum, secretin release stops, which leads to shutdown of pancreatic digestive fluid flow.
Doctors often use a secretin stimulation test to assess pancreatic function, notes the National Library of Medicine encyclopedia MedlinePlus. Patients with pancreatic inflammation, cystic fibrosis or a tumor of the pancreas often have an abnormal secretin stimulation test--the pancreas fails to respond normally to the GI peptide secretin.
Ghrelin
Ghrelin is a hunger-inducing peptide produced by the stomach and, to a lesser extent, the intestine. Other structures, including the hypothalamus and pituitary glands of the brain, the placenta in pregnant women, and the kidneys, also produce small amounts of ghrelin. The levels of ghrelin increase before meals, traveling to the brain to trigger hunger, explains the National Institute of Diabetes and Digestive and Kidney Diseases. Levels of ghrelin fall after a meal, turning off the sensation of hunger.
The role of ghrelin in hunger and body weight remains an area of active biomedical research. In a 2002 landmark study published in "The New England Journal of Medicine," Dr. David Cummings and colleagues report that obese patients who have undergone gastric bypass surgery experience a marked reduction in the total amount of ghrelin produced. The authors conclude that decreasing ghrelin production associated with the procedure contributes to the weight loss that typically occurs with gastric bypass surgery.
References
- Colorado State University Hypertexts for Biomedical Sciences: Endocrine System: Gastrointestinal Hormones, Gastrin
- MedlinePlus: Secretin Stimulation Test
- National Institute of Diabetes and Digestive and Kidney Diseases: Recent Advances and Emerging Opportunities, Obesity
- "The New England Journal of Medicine": Plasma Ghrelin Levels after Diet-Induced Weight Loss or Gastric Bypass Surgery
- Colorado State University Hypertexts for Biomedical Sciences: Endocrine System: Overview of Gastrointestinal Hormones
Member Comments