Ohutsuoli

Ohutsuoli is the Finnish term for the small intestine, the long, coiled section of the digestive tract between the stomach and the large intestine. In humans it is about 6 meters long and is the primary site of digestion and nutrient absorption.

Anatomy and subdivisions: The small intestine consists of three parts. The duodenum is the proximal section, roughly 25–30 cm in length, where chyme mixes with bile and pancreatic juice. The jejunum follows and extends for about 2.5 meters, and the ileum completes the tract with roughly 3.5 meters. The inner lining contains villi and microvilli, forming a large absorptive surface. Enterocytes display brush-border enzymes that aid digestion. The ileum is important for reabsorbing bile acids and, with intrinsic factor, vitamin B12. The lining also houses immune tissue such as Peyer’s patches. Lymphatic lacteals within the villi transport absorbed fats as chylomicrons.

Function and physiology: The small intestine digests and absorbs most nutrients, including carbohydrates, proteins, fats, vitamins, and minerals. It reclaims most of the water and electrolytes from the luminal contents. Fat absorption occurs via chylomicrons entering the lymphatic system. The process is coordinated by the enteric nervous system and hormonal signals, ensuring regulated motility and secretions.

Clinical relevance: Disorders affecting the small intestine include malabsorption syndromes (for example, celiac disease) and inflammatory diseases (such as Crohn’s disease) that can involve any segment, most commonly the ileum. Surgical removal or shortened bowel length can lead to short bowel syndrome, with subsequent nutrient and fluid absorption challenges.