Ileum (20x objective lens)

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This mosaic image made from several sections shows a vertical slice through the full thickness of the wall of the ileum, showing the four layers (from top to bottom):

 

(1) The mucosa (Mu) faces the lumen of the intestine. It consists of a simple columnar epithelium, composed of absorptive cells, called enterocytes (Ent), and mucus-secreting goblet cells (GC). The epithelium rests on a lamina propria (LP) of loose connective tissue. The mucosa is The mucosa is bounded by the muscularis mucosae (MM), a thin layer of smooth muscle that separates the mucosa from the underlying submucosa. Villi (Vi), consisting of finger-like extensions of the mucosa, extend into the lumen and crypts of Lieberkuhn (CL), which are branched tubular intestinal glands, extend from the bases of the villi to muscularis mucosae.

 

(2) The submucosa (SMu) is a layer of composed of dense irregular connective tissue closest to the mucosa and loose connective tissue near the underlying muscle layer. In addition to blood and lymphatic vessels, the submucosa contains ganglia of the parasympathetic branch of the autonomic nervous system, called Meissner's plexi. The most characteristic feature of the ileum is the presence of large lymphoid nodules, called Peyers patches (PP), located in the submucosa, but often breaching the muscularis mucosae to penetrate into the lamina propria of the mucosa. Peyers patches have light-staining germinal centers surrounded by darker staining layers of lymphoid cells.

 

(3) The muscularis externa consists of two layers of smooth muscle - an inner layer (IL) in which the muscle fells are oriented circumferentially around the lumen and an outer layer (OL) in which the muscle cells are oriented parallel to the long axis of the tube. The layers are separated by a thin layer of loose connective tissue (CT) which contains Auerbach's plexi of nerve cells, also part of the parasympathetic branch of the autonomic nervous system.

 

(4) The outermost layer is the serosa (Se), which consists of a simple squamous epithelium of mesothelial cells, and faces the peritoneal cavity. It is continuous with the peritoneum that lines the cavity.

 

Stain = H&E

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	villi	crypts	submucosa	muscularis	serosa

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