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jejunum
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Diagram showing the anatomy of the small intestine with labeled regions (duodenum, jejunum, ileum), a cross-section highlighting muscle and mucosa layers, an enlargement of mucosal folds (plicae circulares), and a detailed view of a villus structure with epithelial, goblet, endocrine, and Paneth cells, microvilli, blood capillaries, and lacteal.
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jejunum

anatomy
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Diagram showing the anatomy of the small intestine with labeled regions (duodenum, jejunum, ileum), a cross-section highlighting muscle and mucosa layers, an enlargement of mucosal folds (plicae circulares), and a detailed view of a villus structure with epithelial, goblet, endocrine, and Paneth cells, microvilli, blood capillaries, and lacteal.
structures of the small intestine The inner wall of the small intestine is covered by numerous folds of mucous membrane called plicae circulares. The surface of these folds contains tiny projections called villi and microvilli, which further increase the total area for absorption. Absorbed nutrients are moved into circulation by blood capillaries and lacteals, or lymph channels.

The jejunum is the middle section of the small intestine, located between the duodenum and the ileum. It constitutes about two-fifths of the small intestine's remaining length after the duodenum. The jejunum is characterized by its deep red color due to a rich blood supply, and it exhibits rapid and vigorous peristaltic movements.1

The primary functions of the small intestine, including the jejunum, are to mix and transport food, produce digestive enzymes, and absorb nutrients. While absorption occurs throughout the small intestine, it is particularly significant in the jejunum. The inner lining of the jejunum is folded into plicae circulares and covered with villi and microvilli, which dramatically increase the surface area for absorption. Sodium ions are absorbed more readily from the jejunum than from other parts of the small intestine, and water absorption also occurs chiefly here.23

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4 Britannica Sources
  1. small intestine
  2. human digestive system - Absorption
  3. jejunum
  4. human digestive system - General features of digestion and absorption

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