Small intestine
Organ where most nutrient absorption occurs in digestion.
The small intestine, also known as the small bowel, is an organ in the gastrointestinal tract where most of the absorption of nutrients from food takes place. It lies between the stomach and large intestine, and receives bile and pancreatic juice through the pancreatic duct to aid in digestion. The small intestine is about 6.5 metres (21 feet) long and folds many times to fit in the abdomen. Although it is longer than the large intestine, it is called the small intestine because it is narrower in diameter.
- length (typical living person)
- 3–5 m (10–16+1⁄2 ft)
- diameter (adult)
- 2.5–3 cm (1–1+1⁄8 in)
- parts
- duodenum, jejunum, ileum
- blood supply
- celiac trunk and superior mesenteric artery
- key function
- absorption of nutrients
Lore & Background
The small intestine has three distinct regions – the duodenum, jejunum, and ileum. The duodenum, the shortest, is where preparation for absorption through small finger-like protrusions called intestinal villi begins. The jejunum is specialized for the absorption through its lining by enterocytes of small nutrient particles which have been previously digested by enzymes in the duodenum. The main function of the ileum is to absorb vitamin B12, bile salts, and whatever products of digestion were not absorbed by the jejunum.
Reader's Guide
The small intestine is central to human digestion and nutrition. It is where most chemical digestion takes place, with enzymes from the pancreas and bile from the liver entering via the pancreatic duct. Proteins, lipids, and carbohydrates are broken down into absorbable forms, such as amino acids, fatty acids, and monosaccharides. The small intestine's enormous surface area, enhanced by folds, villi, and microvilli, allows efficient absorption of nutrients into the bloodstream. Its three sections—duodenum, jejunum, and ileum—each have specialized roles in digestion and absorption. The organ's length varies with individual height and measurement technique, ranging from 3 to 10.5 metres. Understanding the small intestine is essential for diagnosing and treating malabsorption disorders, inflammatory bowel diseases, and other gastrointestinal conditions.
Did You Know?
- The small intestine is about 6.5 metres (21 feet) long but is called 'small' because it is narrower in diameter than the large intestine.
- The small intestine develops from the midgut of the primitive gut tube and rotates anticlockwise between weeks six and ten of embryological life.
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