GI Study Guide - Gastrointestinal(GI review questions and...

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Gastrointestinal (GI) review questions and supplemental notes 1. Describe the different tissue layers of the GI tract. pg 1398 Mucosa - Innermost layer of cells, comprise the lumen of the GI tract. The mucosa is folded into villi and microvilli. The villi serve to enhance the absorptive surface area of the lumen. In the stomach the mucosa contains specialized cells including mucous neck cells, chief cells, parietal cells, and endocrine cells Submucosa - Lies between the mucosa and muscularis, contains blood vessels Muscularis - Lies between submucosa and serosa, contains smooth muscle cells in three layers: oblique, circular, and longitudinal muscle layers. Also contains the submucosal plexus (in the muscularis mucosae) and the myenteric plexus (between the circular and longitudinal muscle layers) Serosa - Outermost layer of cells, lies between the muscularis and visceral peritoneum, contains connective tissue 2. The GI tract is innervated by both divisions of the autonomic nervous system. Describe the overall effects of sympathetic and parasympathetic activation on GI secretory and motor function. PNS (rest and digest) - Innervation arises from the medulla and the sacral spinal cord, has stimulatory effects on the GI secretory and motor function SNS (fight or flight) - Innervation arises from the thoracolumbar region of the spinal cord, which communicates through the prevertebral ganglia. Afferent and efferent nerve fibers converge in the prevertebral ganglia, with afferent fibers returning from the GI tract and efferent fibers exiting to the GI tract. The SNS has inhibitory effects on the GI secretory and motor function Both divisions serve as a “modulatory’ effect and neural fibers from both divisions synapse on interneurons of the intrinsic nervous system. 3. Describe the enteric nervous system and how it is able to sense and coordinate different GI functions. Intrinsic (enteric) nervous system- ability to “sense” and coordinate the secretory and motor response independent of external input from autonomic fibers. Intrinsic vs extrinsic= extrinsic autonomic nerves originate in the CNS and controlled by nerves in the brain ex. Vagus nerve; intrinsic originate within the stomach and respond to local stimuli Is comprised of 2 interconnected nerve plexes: the submucosal and the myenteric The enteric nervous system has mechanoreceptors and chemoreceptors, which can sense and respond to stimuli from the lumen of the GI tract. Ingestion of food activates chemoreceptors, and addition of food to the stomach stretches the stomach, activating mechanoreceptors. This stimuli is detected and communicated by afferent fibers, which are synapsing onto interneurons that compose both the submucosal and myenteric plexus The stimuli results in signals being sent back to the GI tract to via efferent fibers, resulting in a response, for example the secretion of HCl or the contraction of a smooth muscle cell
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  • Spring '16
  • Professor Smith
  • GI Tract

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