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OBJECTIVES

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The student understands the primary mechanisms involved in the short-term regulation of arterial pressure:

  • Identifies the sensory receptors, afferent pathways, central integrating centers, efferent pathways, and effector organs that participate in the arterial baroreceptor reflex.

  • States the location of the arterial baroreceptors and describes their operation.

  • Describes how changes in the afferent input from arterial baroreceptors influence the activity of the sympathetic and parasympathetic preganglionic fibers.

  • Diagrams the chain of events that are initiated by the arterial baroreceptor reflex to compensate for a change in arterial pressure.

  • Describes how inputs to the medullary cardiovascular center from cardiopulmonary baroreceptors, arterial and central chemoreceptors, receptors in skeletal muscle, the cerebral cortex, and the hypothalamus influence sympathetic activity, parasympathetic activity, and mean arterial pressure.

  • Describes and indicates the mechanisms involved in the Bezold–Jarisch reflex, the cerebral ischemic response, the Cushing reflex, the alerting reaction, blushing, vasovagal syncope, the dive reflex, and the cardiovascular responses to emotion and pain.

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The student comprehends the role of the kidney in long-term arterial pressure regulation:

  • Describes baroreceptor adaptation.

  • Describes the influence of changes in body fluid volume on arterial pressure and diagrams the steps involved in this process.

  • Indicates the mechanisms whereby altered arterial pressure alters glomerular filtration rate and renal tubular function to influence urinary output.

  • Describes how mean arterial pressure is adjusted in the long term to that which causes fluid output rate to equal fluid intake rate.

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INTRODUCTION

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Image not available.Arterial pressure is an important variable in the cardiovascular system because it is the driving force that causes blood circulation in the first place. With zero arterial pressure, there would be no flow through any organ and, at the other extreme with high arterial pressure, there is an excessive workload on the heart and potential injury of arterial vessels. Consequently, multiple mechanisms exist for regulating mean arterial pressure to a normal value of about 100 mm Hg.

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Despite the clinical importance of a person’s arterial pressure, it is well to remember that the single most important requirement for proper operation of the cardiovascular system is to provide adequate perfusion of all tissues in the body at all times. At the local level, this is accomplished by regulating local vascular resistance to adjust blood flow to meet local metabolic needs. Because of the parallel arrangement of blood flow to body organs, the system-wide consequence of these individual changes in local vascular resistances is a change in total peripheral resistance (TPR). (For example, when a person is exercising strenuously, TPR is roughly one-third that at rest.) For mean arterial pressure (MAP) to stay constant, the heart must respond to changes in TPR by making reciprocal changes in cardiac output (CO) via adjustments in its heart rate (HR) and stroke volume (SV) (CO = HR × SV). Thus, how well arterial pressure is regulated depends primarily on how well the heart reacts to changes in TPR.

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