Page 196 - Veterinary Histology of Domestic Mammals and Birds, 5th Edition
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178  Veterinary Histology of Domestic Mammals and Birds



                   Table 9.1  Selected enteroendocrine cells of the gastrointestinal system.
       VetBooks.ir  Endocrine cell   Hormone                          Location

                    EC cells
                                     Serotonin
                                                                      Entire gastrointestinal tract
                    ECL cells        Histamine                        Gastric fundus
                    D cells          Somatostatin                     Entire gastrointestinal tract and pancreas
                    G cells          Gastrin                          Stomach and duodenum
                    I cells          Cholecystokinin (pancreozymin)   Small intestine
                    L cells          Glucagon-like peptide            Small intestine, large intestine
                    S cells          Secretin                         Small intestine


                   tein, within membrane-bound endocrine granules. With  and distinctly pale cytoplasm. They are closely apposed
                   the electron microscope, these granules are seen to  (similar to epithelium), forming a collar around the lumen
                   vary in size, shape and density. The features of selected  of the vessel. Electron microscope images show that the
                   recognised enteroendocrine cells are summarised in   number of myofilaments in these specialised muscle cells
                   Table 9.1.                                     is reduced. Within the cytoplasm are irregularly shaped
                      Through paracrine signalling, these hormones regulate  dense secretory granules containing renin.
                   digestive processes by acting upon intestinal motility and   Using electron microscopy, endocrine granules contain-
                   perfusion of the intestinal mucosa.            ing atrial natriuretic peptide (ANP) are observed in the
                                                                  sarcoplasmic reticulum (particularly at the poles of the
                   Additional endocrine cells                     nucleus, near the Golgi apparatus) of certain atrial myo-
                   The tunica media of the afferent arteriole of the glomeruli  cardial cells (myoendocrine cells). The stimulus for release
                   of the kidney contains epithelioid modified smooth mus-  of ANP is stretching of the muscle cells by high-volume
                   cle cells referred to as juxtaglomerular cells. These are  filling of the atria. ANP promotes diuresis and sodium
                   polygonal cells characterised by euchromatic oval nuclei  excretion.






















































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