ch 19 cardio notes

ch 19 cardio notes - 19. The Cardiovascular System: Blood...

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1 19. The Cardiovascular System: Blood Vessels In this chapter we examine blood vessels and properties of flow through these vessels. Each blood vessel falls into one of three major categories: (1) arteries carry blood away from the heart, (2) veins carry blood toward the heart, and (3) capillaries allow diffusion between the blood and surrounding tissues. An adult human has more than ten billion capillaries. I. Overview of Blood Vessel Structure and Function Structure of blood vessel walls Arteries and veins are made of three layers of tissue, which surround a cavity called the lumen (Fig. 19.1). These tissue layers provide strength and flexibility, but they are too thick to allow significant exchange of gases between the blood and surrounding tissues. A. The tunica intima is the innermost layer. It consists of endothelial tissue that lines the blood vessel and an underlying layer of connective tissue with lots of elastic fibers. The endothelial tissue provides a slick surface to minimize friction with the flowing blood. B. The tunica media is the middle layer. It is made of concentric rings of smooth muscle in a framework of loose connective tissue. Collagen fibers bind this layer with the inner and outer layers. This is the thickest layer in arteries. C. The tunica externa is the outermost layer. It is a layer of fibrous connective tissue, which adds strength and support to the vessel. This is generally the thickest layer in veins. Connective tissue fibers of this layer blend into surrounding tissue to anchor the vessels. Arterial system Thick muscular walls give the arteries both elasticity and contractility . Elasticity allows these vessels to respond to and dampen changes in blood pressure generated by pumping of the heart. Contractility allows vasoconstriction and vasodilation in response to signals from the nervous system. Refer back to Chapter 14 (see Table 14.5) and note the general effects of the parasympathetic and sympathetic nervous systems on blood vessels. In traveling from the heart to the capillaries, blood flows through three types of arteries with somewhat different properties (Table 19.1): A. Elastic arteries are large vessels designed to transport large volumes of blood to major regions of the body. The tunica media of these vessels contains large proportions of elastic fibers, and a smaller proportion of smooth muscle. In response to ventricular systole, these vessels expand to accommodate blood from the heart and dampen the increase in pressure. As blood moves through the vessels and the ventricles enter diastole, these vessels contract and dampen the drop in pressure. By the time blood reaches the arterioles, fluctuations in pressure are eliminated. B. Muscular arteries distribute blood throughout the muscles and organs. These vessels contain a higher proportion of muscle than the elastic arteries.
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ch 19 cardio notes - 19. The Cardiovascular System: Blood...

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