Chapter 9

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.

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

• 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.

Appropriate systemic arterial pressure is the single most important requirement for proper operation of the cardiovascular system. Without sufficient arterial pressure, the brain and the heart do not receive adequate blood flow, no matter what adjustments are made in their vascular resistance by local control mechanisms. In contrast, unnecessary demands are placed on the heart by excessive arterial pressure. Thus, although dramatic changes in peripheral resistance and cardiac function can and do occur normally during the course of our normal daily activities, mean arterial pressure is maintained within a narrow range and is tightly regulated. The elaborate mechanisms that have evolved for regulating this critical cardiovascular variable are discussed in this chapter.

Arterial pressure is continuously monitored by various sensors located within the body. Whenever arterial pressure varies from normal, multiple reflex responses are initiated, which cause the adjustments in cardiac output, and total peripheral resistance needed to return arterial pressure to its normal value. In the short term (seconds), these adjustments are brought about by changes in the activity of the autonomic nerves leading to the heart and peripheral vessels. In the long term (minutes to days), other mechanisms such as changes in cardiac output brought about by changes in blood volume play an increasingly important role in the control of arterial pressure. The short- and long-term regulations of arterial pressure are discussed in this chapter.

### Arterial Baroreceptor Reflex

The arterial baroreceptor reflex is the single most important mechanism providing short-term ...

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