FIGURE 17.22 • Electron micrograph and the diagram of a goblet cell. a. This electron micrograph shows the basal portion of a goblet cell depicted on the adjacent diagram. 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 mucous 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. 15,000. b. This diagram shows the entire goblet cell. The boxed region on this diagram represents an area from which the adjacent electron micrograph was most likely obtained. The nucleus is located at the basal portion of the cell. The major portion of the cell is filled with mucinogen granules forming the mucous cup that is evident in the light microscope. At the base and lower sides of the mucous cup are flattened saccules of the large Golgi apparatus. Other organelles are distributed throughout the remaining cytoplasm, especially in the perinuclear cytoplasm in the base of the cell.
restricted to a thin rim of cytoplasm (the theca) that surrounds the apical-lateral portion of the mucinogen granules. Microvilli are more obvious on the immature goblet cells in the deep one half of the intestinal gland.
Paneth cells play a role in regulation of normal bacterial flora of the small intestine.
Paneth cells are found in the bases of the intestinal glands. (They are also occasionally found in the normal colon in small numbers; their number may increase in certain pathologic conditions.) They have a basophilic basal cytoplasm, a supranuclear Golgi apparatus, and large, intensely acidophilic, refractile apical secretory vesicles. These vesicles allow their easy identification in routine histologic sections (Fig. 17.23).
The secretory vesicles contain the antibacterial enzyme lysozyme, -defensins, other glycoproteins, an arginine-rich protein (probably responsible for the intense acidophilia), and zinc. Lysozyme digests the cell walls of certain groups of bacteria. -defensins are homologs of peptides that function as mediators in cytotoxic CD8 T lymphocytes. Their antibacterial action and 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 (see Fig. 17.12). The “closed cells” are concentrated in the lower portion of the intestinal gland, whereas the “open cells” can be found at all levels of each villus. Activation of taste receptors found on the apical cell membrane of “open cells” activates G protein–signaling cascade, resulting in releasing of peptides that regulate a variety of gastrointestinal functions. These include regulating pancreatic secretion, inducing digestion and absorption, and controlling energy homeostasis by acting on neural pathways