Kaksteistsõrmiku

Kaksteistsõrmiku, also known as the duodenum, is the first section of the small intestine in humans and most vertebrates. It is a C-shaped tube that extends from the pylorus of the stomach to the jejunum. The name "duodenum" comes from the Latin word duodeni, meaning "twelve," referring to its approximate length, which is about twelve finger-breadths.

The primary role of the duodenum is to break down food coming from the stomach and absorb nutrients. It receives partially digested food, called chyme, from the stomach and mixes it with digestive juices from the pancreas, liver, and gallbladder. These juices contain enzymes that further break down carbohydrates, proteins, and fats. Bile, produced by the liver and stored in the gallbladder, aids in fat digestion by emulsifying fats.

The walls of the duodenum are lined with villi and microvilli, which are finger-like projections that increase the surface area for nutrient absorption. Essential nutrients like iron, calcium, and vitamins are absorbed in significant amounts within the duodenum. The alkaline environment of the duodenum, maintained by bicarbonate secretions, neutralizes the acidic chyme from the stomach, protecting the intestinal lining and optimizing enzyme activity.

Diseases affecting the duodenum include duodenal ulcers, which are sores that develop on the lining, often caused by H. pylori bacteria or NSAID use. Duodenitis, an inflammation of the duodenum, can also occur. Conditions like celiac disease can damage the duodenal villi, impairing nutrient absorption.