FIGURE 17.23 • Photomicrograph of intestinal glands showing Paneth cells. This photomicrograph shows the base of intestinal (jejunal) glands in an H&E preparation. The gland on the right is sectioned longitudinally; the circular cross-sectional profile of another gland is seen on the left. Paneth cells are typically located in the base of the intestinal glands and are readily seen in the light microscope because of the intensive eosin staining of their vesicles. The lamina propria contains an abundance of plasma cells, lymphocytes, and other connective tissue cells. Note several lymphocytes in the epithelium of the gland (arrows). 240. Inset. This high magnification of the area indicated by the rectangle shows the characteristic basophilic cytoplasm in the basal portion of the cell and large accumulations of intensely staining, eosinophilic, refractile secretory vesicles in the apical portion of the cell. An arginine-rich protein found in the vesicles is probably responsible for the intense eosinophilic reaction. 680.
of brain-gut-adipose axis. 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 17.1). Cholecystokinin (CCK), secretin, gastric inhibitory polypeptide (GIP), and motilin are the most active regulators of gastrointestinal physiology that are released in this portion of the gut (see Fig. 17.13). CCK and secretin increase pancreatic and gallbladder activity and inhibit gastric secretory function and motility. GIP stimulates insulin release in the pancreas, and motilin initiates gastric and intestinal motility. Although other peptides produced by enteroendocrine cells have been isolated, they are not considered hormones and are therefore called candidate hormones (page 584). Enteroendocrine cells also produce at least two hormones, somatostatin and histamine, which act as paracrine hormones (see page 584) (i.e., hormones that have a local effect and do not circulate in the bloodstream). In addition, several peptides are secreted by the nerve cells located in the submucosa and muscularis externa. These peptides, called neurocrine hormones, are represented by VIP, bombesin, and the enkephalins. The functions of these peptides are listed in Table 17.2.
M cells convey microorganisms and other macromolecules from the intestinal lumen to Peyer’s patches.
M cells are epithelial cells that overlie Peyer’s patches and other large lymphatic nodules; they differ significantly from the surrounding intestinal epithelial cells (Folder 17.5). M cells have microfolds rather than microvilli on their apical surface, and they take up microorganisms and macromolecules from the lumen in endocytotic vesicles. The M cell is an antigen-transporting cell. The vesicles are transported to the basolateral membrane where they discharge their contents into the epithelial intercellular space in the vicinity of CD4 T lymphocytes. Thus, substances that gain access to the body from the intestinal lumen via M cells come into contact with cells of the immune system as they reach the basolateral surface. Antigens that reach lymphocytes in this manner stimulate a response in the GALT that is described below.
Intermediate cells constitute the amplifying compartment of the intestinal stem cell niche.