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The small intestine is the site where most of the nutrients from ingested food are absorbed. The inner wall, or mucosa, of the small intestine, is lined with intestinal epithelium, a simple columnar epithelium. Structurally, the mucosa is covered in wrinkles or flaps called circular folds, which are considered permanent features in the mucosa.
The jejunum is the second part of the small intestine in humans and most higher vertebrates, including mammals, reptiles, and birds.Its lining is specialized for the absorption by enterocytes of small nutrient molecules which have been previously digested by enzymes in the duodenum.
Digestion is the breakdown of large insoluble food compounds into small water-soluble components so that they can be absorbed into the blood plasma.In certain organisms, these smaller substances are absorbed through the small intestine into the blood stream.
In fish, the divisions of the small intestine are not as clear and the terms posterior intestine or distal intestine may be used instead of ileum. [2] Its main function is to absorb vitamin B 12 , bile salts , and whatever products of digestion that were not absorbed by the jejunum .
The cecum is a pouch marking the division between the small intestine and the large intestine. It lies below the ileocecal valve in the lower right quadrant of the abdomen. [33] The cecum receives chyme from the last part of the small intestine, the ileum, and connects to the ascending colon of the large intestine. At this junction there is a ...
The intestinal epithelium is the single cell layer that forms the luminal surface (lining) of both the small and large intestine (colon) of the gastrointestinal tract. Composed of simple columnar epithelium its main functions are absorption, and secretion. Useful substances are absorbed into the body, and the entry of harmful substances is ...
The small intestine tract: This is where absorption takes place. [2] [3] [4] The brush borders of the intestinal lining are the site of terminal carbohydrate digestions. The microvilli that constitute the brush border have enzymes for this final part of digestion anchored into their apical plasma membrane as integral membrane proteins.
This facilitates transport of numerous small molecules into the enterocyte from the intestinal lumen. These include broken down proteins, fats, and sugars, as well as water, electrolytes, vitamins, and bile salts. Enterocytes also have an endocrine role, secreting hormones such as leptin.