Ileum

 

  
Small intestine explanatory video

The ileum is  provided with villi which are not as numerous as in the duodenum but are taller.  The mucosa is provided with special lymphatic follicles which extend from the lamina propria to the submucosa.  These are called the Payer’s patches.   It is thrown into folds called valvulae conniventes. Crypts of Lieberkuhn are taller in the ileum than in the duodenum.

Jejunum has thicker and less tall villi when compared with ileum.

Special cells type in the intestine include absorptive cell, paneth cell, mesothelial cell, goblet cell and cells of absorption/secretion called enterocyte

Features of the enterocyte

  1. numerous and dense microvilli
  2. numerous rough endoplasmic reticulum and also mitochondria
  3. numerous Golgi and ribosomes scattered in the cytoplasm
  4. multiple types of junctional specializations which include desmosomes, and tight junctions.

 Paneth cell possesses prominent rough endoplasmic reticulum and also very many crystalline inclusions.   It also contains considerable lysosome and secretory granules which produce peptidases for the process of protein digestion.

 Mesothelial cell is similar in morphology to capillary endothelial cell (see cardiovascular system).   They line the peritoneum on the outermost layer of the intestine-serosa.

 Enteroendocrine cell of the intestine have similar properties as enumerated above for the enteroendocrine cell of the stomach.   The following have been identified in the intestine.

Enteroendocrine cells of small intestine

  1. ECL cell or enterochromaffin like cell which produces histamine
  2. intestinal D cell which produces serotonin
  3. intestinal EC1 cell which produces substance P and serotonin
  4. intestinal M cell which produces motilin
  5. intestinal L cell which produces glicentin
  6. intestinal K cell which produces gastric inhibitory peptide
  7. intestinal N cell which produces neurotensin
  8. intestinal H cell which produces vasoactive inhibitory peptide and porcine heptacosappeptide.
  9. intestinal I cell which produces cholecystokinin,
  10. intestinal P cell which produces bombesin
  11. intestinal IG cell which produces gastrin-34
  12. intestinal S cell which produces secretin.

             Auerbach plexus which is myenteric plexus, is found in the muscularis externa below the circular and longitudinal muscles

            The muscularis externa as 2 layers of muscles only outer longitudinal and inner circular muscle.

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