Tynntarmens

Tynntarmens, in English the small intestine, is a long, coiled section of the digestive tract between the stomach and the large intestine. It is the primary site of chemical digestion and nutrient absorption, and it plays a key role in fluid and electrolyte balance. In humans it consists of three regions: the duodenum, the jejunum, and the ileum, collectively spanning several meters.

The inner lining is highly folded and lined with villi and microvilli, forming a large absorptive surface. Specialized enterocytes absorb digested nutrients, while goblet cells secrete mucus. The duodenum mixes chyme with bile and pancreatic juice; the jejunum handles most carbohydrate and protein absorption; the ileum absorbs bile acids, vitamin B12, and other remaining nutrients. The lacteals within the villi take up absorbed fats into the lymphatic system.

Digestive activity is coordinated by the enteric nervous system and by hormones such as secretin and cholecystokinin. Motility includes segmentation to mix chyme and peristaltic movements to propel contents.

Clinical relevance: malabsorption can result from diseases like celiac disease or Crohn’s disease and can occur after surgical resection. Infections or inflammation can impair absorption and digestion. Understanding the small intestine's structure and function is essential for diagnosing digestive disorders and planning nutrition therapies.