Figure 1623

Electron micrograph of the basal portion of a goblet cell. The cell rests on the basal lamina. The basal portion of the cell contains the nucleus, rough endoplasmic reticulum, and mitochondria. Just apical to the nucleus are extensive profiles of Golgi apparatus. As the mu cous product accumulates in the Golgi cisternae, they become enlarged (asterisks). The large mucinogen granules fill most of the apical portion of the cell and collectively constitute the "mucous cup" seen in the light microscope, x 15,000.

tain pathologic conditions.) They have a basophilic basal cytoplasm; a supranuclear Golgi apparatus; and large, intensely acidophilic, refractile apical secretory granules. These granules allow their easy identification in routine histologic sections (Fig. 16.24).

The secretory granules contain the antibacterial enzyme lysozyme, a-defensins, other glycoproteins, an arginine-rich protein (probably responsible for the intense aci-dophilia), and zinc. Lysozyme digests the cell walls of certain groups of bacteria. a-Defensins are homologues of peptides that function as mediators in cytotoxic CD8+ T lymphocytes. This antibacterial action and their ability to phagocytose certain bacteria and protozoa suggest that Paneth cells play a role in regulating the normal bacterial flora of the small intestine.

Enteroendocrine cells in the small intestine produce nearly all of the same peptide hormones as they do in the stomach

Enteroendocrine cells in the small intestine resemble those that reside in the stomach. They are concentrated in the lower portion of the intestinal gland but migrate slowly and can be found at all levels of each villus (Fig. 16.25). Nearly all of the same peptide hormones identified in this cell type in the stomach can be demonstrated in the enteroendocrine cells of the intestine (see Table 16.1). CCK, secretin, GIP, and motilin are the most active regulators of gastrointestinal physiology that are released in this portion of the gut (see Fig. 16.13). CCK and secretin increase pancreatic and gallbladder activity and inhibit gastric secretory function and motility. GIP stimu-

rhuscularis mucosae

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