Figure 2
Components of the neural, endocrine, and immune systems that regulate GI function.
Essential components discussed in this overview are shown. Vagal afferents emerge from the ganglia between the layers of smooth muscle (circular and longitudinal) surrounding the stomach and small intestine to synapse in the spinal cord and brain (collectively the CNS). In addition, the brain (especially the hypothalamus) relays efferent signals to target organs. The human stomach is divided into 4 regions (cardia, fundus, body [corpus], and antrum). The acid-secreting parietal cells are found in the corpus, whereas the gastrin-producing cells are found in the antrum. Neuroendocrine cells secrete gastric peptides such as ghrelin in the corpus and gastrin in the antrum into the circulation through local capillaries. Similarly, regulatory peptides from neuroendocrine cells in the small intestine and pancreatic islets of Langerhans are secreted into the bloodstream. Collections of immune cells are most prominent in the small intestine as Peyer patches. In addition, the Paneth cells at the base of the intestinal crypts secrete antimicrobial peptides including lysozyme and defensins. Stem cells in the small intestine are anatomically well defined as the 4th cell from the base of the crypt.
