Intestine

The intestine is a long, coiled tube in the digestive system that extends from the pyloric region of the stomach to the anus. In adults it is commonly described as two sections: the small intestine and the large intestine. Its main roles are to digest nutrients, absorb most of the nutrients and water from digested food, and form solid waste for elimination.

The small intestine measures about 6 meters in length and is divided into the duodenum, jejunum, and ileum. The inner surface is lined with villi and microvilli to increase absorptive area. Digestion continues here with enzymes and bile acids; most nutrients are absorbed across the epithelium into the bloodstream, while fats are absorbed into the lymphatic system via lacteals. The ileum reabsorbs bile acids and intrinsic factor–bound vitamin B12.

The large intestine includes the cecum, colon, and rectum and is about 1.5 meters long. Its principal functions are absorbing water and electrolytes and forming solid waste. The colon hosts a dense microbiota that ferment indigestible carbohydrates and produces certain vitamins. Mucus-secreting goblet cells help lubricate stool.

Physiology and circulation: The intestine is controlled by the enteric nervous system and modulated by hormonal signals. Peristaltic movements move contents along. Blood supply comes from the mesenteric arteries, with venous drainage to the portal system; lymphatics drain fats from the mucosa through lacteals.

Clinical notes: Common disorders affect the intestine, including inflammatory bowel disease, celiac disease, and colorectal cancer. Obstruction, infections, and surgical resections can also alter intestinal function.