Clinical note:  A disorder called celiac disease, celiac sprue, or gluten-induced enteropathy, is characterized by intolerance to gluten (a protein in many grains) and results in disappearance of enterocyte microvilli and flattening of the villi and subsequent malabsorption of nutrients. Regeneration of these structures in the small bowel and return of normal nutrient absorption occur after a few weeks on a diet lacking gluten.

What four factors combine to provide a very large surface area for absorption in the small intestine?

Large Intestine (Fig. 15-36) -- site for absorption of water and elimination of solid waste. The three regions (cecum, colon, and rectum) are not very different histologically. Examine a section of the colon (slide 54) and identify the major layers and sublayers (Fig. 15-37).

• Note that the outer layer of muscularis (cut transversely here) does not completely surround the inner layer, but is separated into three more-or-less distinct muscles, the taeniae coli.
• Also, note that myenteric plexi are distinct on this slide.
• The mucosa and submucosa are highly folded in this specimen.
• The mucosa is invaginated into many straight, tightly packed colonic glands, lined by columnar mucus-secreting cells (Fig. 15-37).
• In the lumen, note the solid waste and indigestible material covered with mucus.

Compare and contrast colonic glands with gastric glands.

On slide 6 examine colonic glands cut transversely (Fig. 15-38). Note their small lumens, the mucus-secreting cells, and the many capillaries in the surrounding lamina propria.

What are three histological differences between the large and small intestines?

Now for the pancreas.