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Regulatory processes involved in moving from supine to upright position
Suppose a resting man (supine) is awakened by an alarm clock. Before the alarm goes off, the parasympathetic tone dominates the autonomic nervous system and a small trickle of saliva drools from the man's mouth. Heart rate has slowed (M2-muscarinic receptors), intestinal motility and glandular secretion is increased (M1/M3-muscarinic receptors), and the man experiences an involuntary erection (M3-receptors).
As the man awakens, the resting parasympathetic tone in all autonomic systems begins to swing toward more sympathetic tone. As the man sits up, blood flows away from his head, mean blood pressure decreases, and the baroreceptors in the arotic arch and carotid sinus reduce their firing rate because of decreased stretch. This decrease in afferent firing is interpreted in the CNS cardiovascular control center (alpha2-receptors) as a signal to increase sympathetic outflow and decrease parasympathetic outflow.
Increased sympathetic outflow will cause increased firing rate of preganglionic neurons and increased firing of sympathetic postganglionic neurons (ganglionic N1-nicotinic receptors). The increased sympathetic outflow releases NE at alpha1-adrenergic receptors in the arterioles causing contraction of smooth muscle and vasoconstriction leading to increased blood pressure. Increased sympathetic outflow also causes increased heart rate (beta1-receptors), vasodilation of bronchial smooth muscle (beta2-receptors), and decrease of intestinal motility (M1/M3-muscarinic receptors). Stimulation of the adrenal medulla by the sympathetic outflow causes release of epinephrine into the blood producing vasodilation and increase contractility of skeletal muscle (beta2-receptors).
Try writing a similar paragraph for the same situation but assume that the subject is being
treated for hypertension with propranolol and prazosin.
Adapted from Figures 31-7 & 31-8: StatRef Online Library: Basic and Clinical Pharmacology 8th ed. (2001)
by Michael Bolger, 8/26/01
Copyright(c) 2001 The McGraw Hill Companies, Inc. All rights reserved
Last updated 8/26/01
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