CorpusHuman Anatomy

Intestinal Villus and Absorption

Villi, crypts and the absorptive enterocyte: where sugars, amino acids and fats leave the gut

The left panel is a section through the small-intestinal mucosa. Finger-like villi project into the lumen and crypts of Lieberkühn dip between them down to the muscularis mucosae. The left-hand villus is cut open to show its microcirculation: an arteriole climbs to the tip, breaks into a subepithelial capillary network, and drains into a venule. A blind-ended central lacteal runs down the core to the submucosal lymphatics. Stem cells at each crypt base, flanked by granular Paneth cells, make new epithelial cells that migrate up the villus and are shed at its tip within about 3–5 days (animated accent dots).

The right panel magnifies the epithelium. Enterocytes carry a microvillous brush border and are sealed by tight junctions, with a mucus-secreting goblet cell between them. The animation shows the three absorption routes. Sugars enter by SGLT1 (Na⁺-coupled glucose and galactose) and GLUT5 (fructose) and leave by GLUT2. Amino acids and di- and tripeptides enter by Na⁺-coupled carriers and PepT1. Both pass into the fenestrated capillary towards the hepatic portal vein. Lipids arrive in micelles, are re-esterified in the smooth ER, packaged with apoB-48 in the Golgi into chylomicrons, and exocytosed into the lacteal towards the thoracic duct.

Step-by-step

  1. Villi multiply the surface

    Villi about 0.5–1 mm tall cover the circular folds and increase the absorptive surface about tenfold. The microvilli of each enterocyte add about twentyfold more.

  2. Enterocytes and the brush border

    Tall columnar absorptive cells sealed by tight junctions. Their brush border carries digestive enzymes (disaccharidases, peptidases) and nutrient transporters.

  3. Goblet cells

    Goblet cells secrete mucin that hydrates into a protective mucus layer. They become more numerous towards the ileum and colon.

  4. Crypts: stem cells and Paneth cells

    Each crypt is a regenerative and secretory gland. Stem cells at the base are flanked by Paneth cells, which secrete defensins and lysozyme. Crypt cells also secrete Cl⁻ and water through CFTR.

  5. Epithelial renewal

    New cells migrate from crypt to villus tip and are shed after about 3–5 days, so the epithelium is replaced every few days.

  6. Sugars → blood

    Glucose and galactose enter with 2 Na⁺ on SGLT1 and fructose enters on GLUT5. All three leave on GLUT2 into fenestrated capillaries, which drain to the hepatic portal vein. The basolateral Na⁺/K⁺-ATPase powers the uptake.

  7. Amino acids and peptides → blood

    Free amino acids enter on Na⁺-coupled carriers, and di- and tripeptides on H⁺-coupled PepT1. Cytosolic peptidases release amino acids, which leave basolaterally into the capillaries.

  8. Fats → chylomicrons → lacteal

    Micelles deliver monoglycerides and fatty acids to the brush border. The smooth ER re-esterifies them into triglyceride, and the Golgi packages this with apoB-48 into chylomicrons. These are too big for blood capillaries, so they enter the lacteal and reach the blood through the thoracic duct.

Labelled parts