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INTRODUCTION

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Blood moves through the vascular system secondary to pressure and osmotic gradients similar to a plumbing system, but, unlike our household pipes, the system of blood vessels is not made up of static and inflexible structures. The vascular system is dynamic and always changing to regulate blood flow to the body and its essential organs. The system of blood vessels with the heart at its center is critical for delivering oxygenated blood and essential nutrients to organs and tissues and removing and transporting waste products.

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This chapter will cover the normal circulatory system and its structures and congenital and acquired diseases including atherosclerosis, trauma, and inflammatory and infectious processes. The pulmonary vascular system and its diseases will also be discussed.

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EMBRYOLOGY OF BLOOD VESSELS

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The cardiovascular system develops very early in gestation (as early as 15–16 days) due to the limited energy sources available from the egg and yolk sac. The cardiovascular system delivers nutrients to the increasingly actively dividing cells and disposes of waste products through its connections with the maternal vasculature of the placenta. The heart and blood vessels are created from the mesoderm that forms blood islands (isolated cell masses) around which the endothelial tubes are formed. Vascular smooth muscle cells and connective tissue derived from the local mesoderm then surround the endothelial tubes. The heart begins to beat and blood begins to circulate throughout the blood vessel network around the 4th week of gestation (Figure 7-1).

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FIGURE 7-1

Embryological development of blood vessels. In the extraembryonic yolk sac, mesodermal precursor cells aggregate to form blood islands, the sites of development of endothelial and primitive blood cells. Within the blood islands, centrally-located cells become primitive blood cells, whereas outer cells give rise to endothelial cells (ECs). ECs then form the vascular primary plexus which is subsequently remodeled to form the yolk sac vasculature. In the embryo proper, mesodermal precursor cells differentiate into the vascular primary plexus and major vessels, aorta, and cardinal vein. After arterial and venous ECs are specified, the complex blood vasculature is formed via extensive remodeling. At embryonic day (E) 9.5, a subset of ECs of the cardinal vein acquires a lymphatic endothelial cell (LEC) fate and develops into lymphatic vessels. From Park C, Kim TM, Malik AB.Transcriptional regulation of endothelial cell and vascular development. Circ Res. 2013;112:1380–1400.

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QUICK REVIEW Normal Anatomy of Blood Vessels

Blood vessels consist of arteries, veins, and capillaries that are categorized according to their structure, size, and function. The arterial system carries oxygenated blood away from the heart to the organs and periphery providing oxygen and nutrients to the cells at a distance. The capillary system is responsible for the exchange of new supplies and the waste products. The venous system carries the deoxygenated blood with its waste products back ...

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