APPENDIX

Slide #133 (human) - methacrylate.  Again, determine where the muscularis mucosae lies; are there any strands of smooth muscle visible among the lymphocytes?

Look at the mucosa and submucosa for unusually numerous eosinophils.  Look closely also at any pale germinal centers you may find in the lymphatic tissue; you are likely to see numerous mitotic figures there, as well as large Ablast@ cells.  Compare the size of the large lymphoblasts and plasmoblasts with the much smaller size of the typical lymphocytes (mostly B cells probably) seen surrounding the germinal centers.

Now look at the bases of the crypts of Lieberkuhn for Paneth cells and enteroendocrine cells.  The Paneth cells have bright, seed-like, orange-pink granules in an apical location.  The enteroendocrine cells (called variously enterochromaffin, argentaffin, and argyrophil cells because of special staining properties) have much finer, orange-pink granules in a basal position, where they can be secreted directly into surrounding capillaries for distribution in the blood stream.  These endocrine cells are found in the crypt-lining throughout the intestines and are part of a diffuse endocrine system, sometimes referred to as neuroendocrine cells or, alternatively as the APUD systems (amine precursor uptake and decarboxylation) because of the histochemical properties of their peptide secretory granules.  Among the parahormones credited to the enteroendocrine cells of the intestines are cholecystokinin, gastrin, serotonin and secretin.  Read about their functions in digestion.

While looking at the appendix, find the site of the mesenteric attachment and not the presence of blood vessels there: both arteries and veins.  They are likely to be thin-walled lymph vessels also, some of them with good valves.