18: Cardiovascular System - Blood Vessels and Circulation
The blood vessels form the distribution network of the cardiovascular system. Each specific type of vessel has specialized anatomy that is critical to keep blood circulating through both circuits of blood flow to collect and distribute nutrients, collect and deliver waste products for removal, deliver hormonal signals to adjust body functions, and help the body maintain homeostasis. (Thumbnail image credit: Human Heart and Circulatory System by Bryan Brandenburg is licensed under CC BY 3.0 )
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- 18.1: Introduction to Blood Vessels and Circulation
- In this chapter, you will learn about the vascular part of the cardiovascular system, that is, the vessels that transport blood throughout the body and provide the physical site where gases, nutrients, and other substances are exchanged with body cells. When vessel functioning is reduced, blood-borne substances do not circulate effectively throughout the body. As a result, tissue injury occurs, metabolism is impaired, and the functions of every bodily system are threatened.
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- 18.2: Structure and Function of Blood Vessels
- Blood is carried through the body via blood vessels. An artery is a blood vessel that carries blood away from the heart, where it branches into ever-smaller vessels. Eventually, the smallest arteries, vessels called arterioles, further branch into tiny capillaries, where nutrients and wastes are exchanged, and then combine with other vessels that exit capillaries to form venules, small blood vessels that carry blood to a vein, a larger blood vessel that returns blood to the heart.
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- 18.3: Circulatory Pathways
- Virtually every cell, tissue, organ, and system in the body is impacted by the circulatory system. This includes the generalized and more specialized functions of transport of materials, capillary exchange, maintaining health by transporting white blood cells and various immunoglobulins (antibodies), hemostasis, regulation of body temperature, and helping to maintain acid-base balance. In addition to these shared functions, many systems enjoy a unique relationship with the circulatory system.
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- 18.4: Development of Blood Vessels and Fetal Circulation
- In a developing embryo,the heart has developed enough by day 21 post-fertilization to begin beating. Circulation patterns are clearly established by the fourth week of embryonic life. It is critical to the survival of the developing human that the circulatory system forms early to supply the growing tissue with nutrients and gases, and to remove waste products. Development of these circulatory elements within the embryo itself begins approximately 2 days later.