Structure and Functions (Magill’s Medical Guide, Sixth Edition)
The vascular system is faced with the enormous task of supplying every cell of the human body with a constant supply of oxygen and nutrients needed to sustain life. This elaborate system circulates more than 2,000 gallons of blood per day through more than 12,000 miles of arteries, veins, and capillaries. Moreover, the job of the vascular system is not done when the nutrients arrive at the cell. After the cell uses the nutrients, waste products that are left over from metabolism must be carried away and disposed of before they damage the cell. For this reason, several kinds of vessels exist within the human body that differ in structure and function. They can be broken into three categories: arteries, veins, and capillaries.
The term “arteries” came from ancient times, when arteries were thought to be filled with air. (This misconception evolved because after death much of the blood usually pumped through the arteries had been pumped out, leading scientists of the time to conclude that air, rather than blood, was circulated within them.) Arteries are thick-walled blood vessels that carry oxygen-rich blood from the left side of the heart to all parts of the body. The blood circulating within them is usually moving at high velocities and exerts pressure against the artery walls, creating an expansion of the artery during the contraction of the heart. This expansion, called a pulse, can be palpated in areas where the...
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Disorders and Diseases (Magill’s Medical Guide, Sixth Edition)
When the vascular system is functioning correctly, all the cells of the body are receiving the right amount of blood at all times. Many problems can arise, however, in the complex functioning of the human organism, and the vasculature must have ways of meeting these challenges. Such problems include the obstruction of vital vessels by plaque formation (a buildup of fatty deposits called atherosclerosis), thrombus (blood clot) formation, and vasospasm (a closing down of a blood vessel in response to cold or trauma). Moreover, some organs in the body cannot survive for more than a few minutes without oxygen before damage occurs. For example, the brain can survive for only a few minutes without oxygen, while the cells in the arms and legs can be deprived of oxygen for a matter of hours without irreversible damage. For this reason, whenever there is a problem the vascular system must be able to set priorities about which systems receive blood flow and which systems do not. When there is a life-threatening problem, the vessels in the arms and legs contract, forcing blood out of the extremities; this allows more flow to reach the brain, where it is most urgently needed. When an artery is narrowed by plaque, the vascular system will compensate by enlarging smaller vessels in the area to help maintain flow. If the artery is totally obstructed, this system of collateral vessels takes over.
While these and other mechanisms work...
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Perspective and Prospects (Magill’s Medical Guide, Sixth Edition)
The vasculature of the human body has not always been understood, even in recent times. The ancient Egyptians knew about the importance of the heart and the pulse, but this knowledge was not passed on to more modern civilizations. Hippocrates (c. 460-c. 370 b.c.e.) had serious misconceptions about the functions of the circulatory system: He thought that the pulse was caused by movements of the blood vessels. Other great thinkers such as Aristotle and Galen made similar errors in their study of the vascular system, errors that influenced medicine for many years.
In 1628, a doctor in London named William Harvey published a paper introducing his radical theories about how the blood circulates. He changed the way medical people thought about this system by describing it as a closed circuit, with blood being forced through it via contractions of the heart. He postulated that blood passed from the arteries into the veins at the cellular level. It was not until the 1660’s, when early microscopes were developed, that this theory could be confirmed.
In 1733, a clergyman named Stephen Hales became the first person to measure blood pressure within the arterial system. He inserted a large, hollow glass tube into the neck artery of a horse. To his amazement, the blood rose 9 feet up the tube. This method of measuring blood pressure was not practical, however, and it was not until the late nineteenth century that the...
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For Further Information: (Magill’s Medical Guide, Sixth Edition)
Hershey, Falls B., Robert W. Barnes, and David S. Sumner, eds. Noninvasive Diagnosis of Vascular Disease. Pasadena, Calif.: Appleton Davies, 1984. This book, written for medical personnel, may be difficult reading for the layperson. Nevertheless, it is valuable for its detailed description of the anatomy, physiology, and pathology involved in vascular disease, as well as for its discussion of diagnostic methods.
Loscalzo, Joseph, and Andrew I. Schafer, eds. Thrombosis and Hemorrhage. 3d ed. Philadelphia: Lippincott Williams & Wilkins, 2003. Covers an array of relevant topics, including the basic elements of hemostasis, the normal function and response of platelets, thrombotic disorders, and the management of patients with hemorrhagic and thrombotic conditions.
Milady’s Standard Textbook of Cosmetology. Clifton Park, N.Y.: Thomson/Delmar Learning, 2008. Although this is a cosmetology textbook, it contains a short and concise chapter on arteries, veins, and capillaries that is very clearly written. Written for a lay audience, this work is an excellent source for gaining a better understanding of the basics of circulation.
Mohrman, David E., and Lois Jane Heller. Cardiovascular Physiology. 6th ed. New York: Lange Medical Books/McGraw-Hill, 2006. Provides a thorough overview of the basic concepts of cardiovascular physiology and reviews recent scientific research...
(The entire section is 290 words.)