GASTROINTESTINAL SYSTEM IV: LABORATORY

DEMONSTRATION:

Check the microscopes at the front of the laboratory. See Demo H-4 (ileum), DEMO H-3 (colon) and DEMO H-28 (colon with alcian blue stain for mucin).

Review the four major tissue coats of the G.I. tract. Review the components of each coat.

Slides 30, 125, 33: small intestine:

Identify the crypts of Lieberkuhn (intestinal glands) and villi.
Examine the three regions of the small intestine as follows:

The duodenum: - has Brunner's (mucous) glands in submucosa.
The jejunum: - lacks Brunner's glands.
The ileum: - lacks Brunner's glands. The mucosa and submucosa have groups of lymph nodules on the antimesenteric surface called Peyer's patches.

Examine slide 30 of duodenum

Find Brunner's glands. Brunner's glands are found only in proximal duodenum. Identify crypts and villi. Find some cross-sections of villi and crypts. Compare them. Note the striated border on the villi. Identify the two types of epithelial surface cells and review the fine structure and function of each. In addition to goblet and absorptive cells, identify Paneth cells in the base of the crypts; they contain large acidophilic apical granules. Note Auerbach's plexus in the muscularis propria.

Examine slide 125 of jejunum

Again, notice how similar jejunum is to duodenum and ileum. On high power, note the striated border which is very prominent in this slide. Of what is it formed? Note the shape and staining properties of the goblet cell. Try to find a central lacteal. In the submucosa, find the parasympathetic post-ganglionic cell bodies of Meissner's plexus. Find Auerbach's plexus in the muscularis propria.

Examine slide 33 of ileum

Note the diffuse and nodular lymphatic tissue of Peyer's patches in the ileum. Note that you can see Peyer's patches by gross examination of the slide.

Slides 35, 74, 126: colon:

Distinguish colon from small intestine by the following features:

Examine slide 35 and 126 The colon lacks intestinal villi but possesses intestinal glands.
More goblet cells are present in colonic epithelium than are found within the small intestine.
Solitary lymph nodules in the lamina propria often extend into the submucosa (are not confluent as in Peyer's patches).
Note that the longitudinal smooth muscle layer of the muscularis propria is gathered into 2 or 3 taenia coli and exists as a thin layer of muscle between adjacent taenia (best seen on slide 74).

Slide 34: appendix:

Note the numerous mucous cells in the simple columnar epithelium. The overall size is small and the lumen folded. Villi are absent but crypts are present.
Confluent lymphatic nodules are present.
The lamina propria is very cellular.
The longitudinal layer of the muscularis propria is continuous and taeniae coli are not present.

Slide 76: recto-anal junction:

Note the change in epithelial configuration at the recto-anal junction. What happens to the mucous cells? What epithelium is found in the rectum and in the anal canal?
Identify the large, blood-filled hemorrhoidal veins in the wall of the anal canal.
Identify apocrine sweat glands, hair follicles and sebaceous glands. These are present in some slides but not in others.