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OBJECTIVES

OBJECTIVES

After studying this chapter, you should be able to:

  • Contrast the sympathetic and parasympathetic control of the heart and vasculature.

  • Identify the components and neurotransmitters in the central neural pathways that control arterial blood pressure and heart rate and list factors that determine the activity within the pathways.

  • Identify the locations of the receptors and afferent and efferent pathways, the effector responses, and the functions of the baroreceptor reflex pathway.

  • Describe the role of atrial and cardiopulmonary receptors in the control of the cardiovascular system in health and disease.

  • Contrast the locations, properties, and functions of the peripheral and central chemoreceptor reflexes.

  • Define how the process of autoregulation contributes to control of vascular caliber.

  • Identify the paracrine factors, particularly those secreted by the endothelium, that regulate vascular tone and their mechanisms of action.

  • List circulating vasodilators and vasoconstrictors.

INTRODUCTION

Multiple cardiovascular regulatory mechanisms exist that help increase the blood supply to active tissues and increase or decrease heat loss from the body by redistributing the blood. In the face of challenges such as hemorrhage, they maintain blood flow to the heart and brain. When the challenge faced is severe, flow to these vital organs is maintained at the expense of the circulation to the rest of the body.

Circulatory adjustments are effected by altering the output of the pump (the heart), changing the diameter of the resistance vessels (primarily the arterioles), or altering the amount of blood pooled in the capacitance vessels (the veins). Regulation of cardiac output is discussed in Chapter 30. The caliber of the arterioles is adjusted in part by autoregulation (Table 32–1). It is also increased in active tissues by locally produced vasodilator metabolites and substances secreted by the endothelium. The diameter of the arterioles is also regulated by circulating vasoactive substances and the sympathetic nerves that innervate them. Circulating vasoactive substances and sympathetic nerves also determine the caliber of the capacitance vessels. The systemic regulatory mechanisms synergize with the local mechanisms and adjust vascular responses throughout the body.

The terms vasoconstriction and vasodilation are generally used to refer to constriction and dilation of the resistance vessels. Changes in the caliber of the veins are referred to as venoconstriction or venodilation.

NEURAL CONTROL OF THE CARDIOVASCULAR SYSTEM

INNERVATION OF THE BLOOD VESSELS

Most of the vasculature is an example of an autonomic effector organ that receives innervation from the sympathetic but not the parasympathetic division of the autonomic nervous system (see Chapter 13). Sympathetic postganglionic fibers terminate on vascular smooth muscle in all parts of the body and release norepinephrine to act on α1-adrenoceptors to mediate vasoconstriction. In the vasculature of exercising muscles, activation of the sympathetic nervous system and release of epinephrine from the adrenal medulla can also mediate vasodilation by the activation of β2...

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