Kaksteistsõrmiksoolde

Kaksteistsõrmiksoolde, also known as the duodenum, is the first section of the small intestine in the digestive system of humans and many other vertebrates. It immediately follows the stomach and precedes the jejunum, the second part of the small intestine. The name "duodenum" is derived from the Latin word for "twelve," referring to its approximate length, which is about twelve fingerbreadths.

The primary functions of the duodenum are to neutralize stomach acid and to chemically digest food. It receives chyme, the semi-liquid mass of partially digested food, from the stomach. Here, it mixes with digestive juices from the pancreas, liver, and gallbladder. Pancreatic enzymes break down carbohydrates, proteins, and fats. Bile, produced by the liver and stored in the gallbladder, emulsifies fats, making them easier to digest. Bicarbonate ions secreted by the duodenal walls also neutralize the highly acidic chyme from the stomach, creating an optimal pH for pancreatic enzymes to function.

The wall of the duodenum contains specialized glands that secrete mucus and bicarbonate. The presence of food in the duodenum stimulates the secretion of hormones like secretin and cholecystokinin (CCK). Secretin signals the pancreas to release bicarbonate, while CCK prompts the gallbladder to release bile and the pancreas to release digestive enzymes. The inner lining of the duodenum has folds, villi, and microvilli that significantly increase its surface area for efficient absorption of nutrients, although most nutrient absorption primarily occurs in the jejunum and ileum.