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The circular folds slow the passage of the partly digested food along the intestines, and afford an increased surface for absorption. [4] They are covered with small finger-like projections called villi (singular, villus). Each villus, in turn, is covered with microvilli. The microvilli absorb fats and nutrients from the chyme.
These folds together with villi serve to increase the surface area of the jejunum enabling an increased absorption of digested sugars, amino acids and fatty acids into the bloodstream. The circular folds also slow the passage of food giving more time for nutrients to be absorbed. The last part of the small intestine is the ileum.
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.
In the small intestine, villi are folds of the mucosa that increase the surface area of the intestine. The villi contain a lacteal, a vessel connected to the lymph system that aids in the removal of lipids and tissue fluids.
The combination of the circular folds, the villi, and the microvilli increases the absorptive area of the mucosa about 600-fold, making a total area of about 250 m 2 (2,700 sq ft) for the entire small intestine. [20] Its main function is to absorb the products of digestion (including carbohydrates, proteins, lipids, and vitamins) into the ...
The jejunum has many large circular folds in its submucosa called plicae circulares that increase the surface area for nutrient absorption. The plicae circulares are best developed in the jejunum. There is no line of demarcation between the jejunum and the ileum. However, there are subtle histological differences:
The ileum (/ ˈ ɪ l i əm /) is the final section of the small intestine in most higher vertebrates, including mammals, reptiles, and birds.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]
Enterocytes, or intestinal absorptive cells, are simple columnar epithelial cells which line the inner surface of the small and large intestines. A glycocalyx surface coat contains digestive enzymes. Microvilli on the apical surface increase its surface area.