Corpus: Small intestine
1. Definition
The small intestine is the part of the gastrointestinal tract that extends from the stomach outlet (pylorus) to the ileocecal valve. Its primary function is the absorption of nutrients and water from ingested food.
2. Classification
The small intestine is divided into three sections of varying lengths:
The duodenum, at about 24 cm long, is the shortest section. In total, the small intestine in adults measures around 5 to 6 meters in length. Except for parts of the duodenum, the small intestine is located intraperitoneally.
3. Anatomy
The small intestine lies in folded loops in the central part of the abdominal cavity. Except for portions of the duodenum, it is suspended from the posterior abdominal wall by a mesentery. The small intestine is framed on three sides by the colon, which extends downward into the space below the superior pelvic aperture.
3.1. Arterial supply
The small intestine receives its arterial blood supply from the following vessels:
4. Histology
To enhance absorption, the small intestine features anatomical and fine tissue structures that significantly increase its surface area. Instead of having a smooth surface, the mucosa of the small intestine is wrinkled into folds. These folds, which can reach up to 1 cm in height, are known as circular folds. Both the mucosa and submucosa are involved in the formation of these folds, but the muscular layer is not.
A distinguishing feature of the small intestinal mucosa is its organization into finger-shaped or leaf-shaped projections and crypts (also known as crypts of Lieberkühn), which are tubular depressions.
The epithelial layer of the small intestine consists of a single-layered cylindrical epithelium. The surface of the epithelial cells facing the intestinal lumen is densely packed with microvilli, which further increase the surface area for absorption.
5. Physiology
The small intestine plays a vital role in the digestion and absorption of various food components. The chyme (partially digested food) is propelled forward through the intestine by peristaltic movements of the intestinal wall, ensuring proper mixing with digestive enzymes and facilitating nutrient absorption.