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Metabolic Organs: The Small Intestines
Tashira Persia M.D.
Physician Reviewed
What are the Small Intestines?
The small intestine is the longest section of the gastrointestinal tract. It is located in the abdominal cavity and connects the stomach to the large intestine. Its main functions include the absorption of nutrients and water, as well as the secretion of enzymes/hormones that help break down food.
It is divided into three parts:
Duodenum
Produces digestive juices and enzymes to break down food. When food enters the small intestine, it stimulates I-cells to release cholecystokinin (CCK), a hormone that causes the gallbladder to contract and release bile acids (which aid in digestion) and relaxes the sphincter of Oddi to allow bile to enter the duodenum. The pancreas also releases digestive enzymes to assist in the digestive process.
Jejunum
Responsible for mixing food with digestive enzymes through churning movements.
Ileum
The final part of the small intestine. It absorbs nutrients such as proteins, fats, carbohydrates, and minerals that have been broken down by the previous sections. It then moves the remaining waste into the large intestine.
The Small intestine as a metabolic organ
Nutrients trigger metabolic and sensory signaling pathways in the lining of the small intestine. This can cause effects throughout the body even before the nutrients enter the bloodstream. Enteroendocrine cells, which are distributed throughout the intestine, sense nutrients, activate different pathways, and ultimately stimulate the secretion of gut hormones.
The small intestine plays an important role in glucose homeostasis. GLUT2 (glucose transporter 2) and SGLT1 (sodium-glucose co-transporter 1) are located on the membranes of enterocytes (intestinal cells) and facilitate the transport of glucose from the small intestine into the bloodstream. SGLT1 is being investigated as a therapeutic target in type II diabetes mellitus. While most current therapies (e.g., SGLT2 inhibitors) act at the kidney level, dual SGLT1/SGLT2 inhibition or selective intestinal SGLT1 inhibition may help reduce postprandial glucose excursions by delaying glucose absorption and enhancing incretin release.
GLP-1 and the small intestine
Glucagon-like peptide-1 (GLP-1) is produced by L-cells, which are specialized enteroendocrine cells mainly found in the distal ileum and colon, but also present in the jejunum and duodenum. The amount of GLP-1 produced in the body is not strong enough to sustain a therapeutic effect and does not last very long. Injectable GLP-1 medications are engineered to last longer and produce sustained therapeutic effects.
One of the effects of GLP-1 is to decrease gastric emptying by reducing peristalsis (the cyclic movements of the gastrointestinal tract). This leads to decreased appetite and increased feelings of fullness.
Conclusion
Even though the body produces many hormones to regulate different metabolisms in the body, they are not always as potent as needed and may not produce the desired effects. Because of this, exogenous GLP-1 molecules were developed to enhance the beneficial effects of this pathway, leading to weight loss and improved glucose control.
At Covenant Metabolic Specialists, we collaborate with entities studying the efficacy of molecules that enhance already established effects, as well as potential new benefits such as reducing hepatic fat accumulation, inflammation, and fibrosis in the liver.
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