122)There are two types of alpha receptors and two types of beta receptors. The alpha-1 receptor produces excitation orstimulation of metabolism. It works by activation of an enzyme and/or by release of calcium ion from internal stores.The alpha-2 receptor is inhibitory on its target cell by reducing the level of cAMP. Beta-1 receptors are stimulatingand/or lead to increased energy consumption. They activate cellular enzymes. Beta-2 receptors inhibit activity orproduce relaxation in smooth muscle cells. They operate through enzyme activation.123)You would want to use a beta-blocker, because the stimulation of beta-1 receptors increases heart rate. By blockingthese receptors, parasympathetic influence will predominate and the heart will slow down.124)The vagus nerve carries parasympathetic preganglionic fibers to many organs within the ventral cavity, including thedigestive organs. It stimulates gastric motility and secretion of acid and enzymes. Removing the vagus innervation willeliminate parasympathetic stimulation, leaving only sympathetic innervation, which is inhibitory. This procedure willthus greatly reduce gastric activity. Hormonal stimulation will remain but higher centers will no longer influencesecretion of gastric juice.22
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