Arteries . The circulatory system, made up of arteries and veins , is essential for maintaining life. Its function is the delivery of oxygen and nutrients to all cells , as well as the removal of carbon dioxide and waste products, the maintenance of physiological PH, and the mobility of the elements, proteins and cells of the immune system. In developed countries, the two leading causes of death, myocardial infarction and stroke, are both the direct result of the slow and progressive deterioration of the arterial system, a process that can last for years.
Histology
The arteries are membranous, elastic conduits, with divergent branches, responsible for distributing throughout the body the Blood expelled from the ventricular cavities of the Heart at each systole. Each arterial vessel consists of three concentric layers: 1. Internal or intimate: made up of the endothelium (a simple flat epithelium), a basal lamina and a subendothelial conjunctiva layer. The intima is present in all vessels (arteries or veins) and its composition is identical in all. The classification of the vessels therefore depends on the histological description of the other two layers.
2. Medium: composed of smooth muscle fibers arranged concentrically, elastic fibers and collagen fibers, in variable proportions depending on the type of artery. In arteries, the media is a compact-looking layer of regular thickness.
3. External: formed by loose connective tissue, mainly composed of fibroblasts and collagen. In arteries with a diameter greater than 1 mm, the nourishment of these tunics or layers is carried out by the vasa vasorum; its innervation, of the nervi vasorum (vasomotor phenomena).
The boundaries between the three layers are generally well defined in the arteries. The arteries always present an internal elastic lamina separating the intima from the media, and (with the exception of the arterioles) present an external elastic lamina that separates the media from the adventitia. The outer elastic lamina is often continuous with the elastic fibers of the adventitia. In the general or systemic circulation, the Blood that is driven out of the heart passes through a system of arterial vessels of increasingly reduced diameter, until it reaches the Tissues , and then returns to the Heart through the venous system.
Layers
Internal or intimate tunic
It is lined by an epithelium, which rests on a small sheet of loose connective tissue.
Half tunic
It is the thickest of its layers, it contains smooth muscle and elastic tissue.
External or adventitial tunic
It is the strongest of the three layers, rich in elastic collagen fibers. It has small blood vessels called vasa vasorum, autonomic and sensory nerve fibers, some of which are sensitive to painful stimuli.
Structure of blood vessels
Elastic arteries
They make up the great arteries, such as the aorta, pulmonary artery, carotid artery, subclavian artery or the brachiocephalic trunk. In this case, the stocking is formed by a succession of concentric elastic sheets, between which the smooth muscle cells are arranged. The external and internal elastic laminae are more difficult to distinguish than in the muscular arteries, due to the importance of the elastic component of the stocking. The predominance of elastic components is essential for the pulsatile property of the arteries.
Muscular arteries
They constitute the small and medium arteries of the body. The stocking forms a compact, essentially muscular layer with a fine network of elastic sheets. The internal and external elastic blades are well visible. Example: coronary arteries. Most of the blood volume is found in the veins and venules, while the greatest pressure drop occurs in the small arteries and arterioles.
Arterioles
They are the smallest arteries and contribute fundamentally to the regulation of blood pressure, through the variable contraction of the smooth muscle of their walls, and to the regulation of blood supply to the capillaries. In fact, the main regulation of global blood flow and general blood pressure occurs through the collective regulation of the arterioles: they are the main adjustable tubes in the blood system, where the greatest pressure drop takes place. The combination of cardiac output and systemic vascular resistance, which refers to the collective resistance of all arterioles in the body, are the main determinants of blood pressure at any one time.
Capillaries
Capillaries are the regions of the circulatory system where the exchange of substances with adjacent tissues takes place: gases, nutrients or waste materials. To promote exchange, capillaries have a single endothelial cell that separates them from tissues . Also, the capillaries are not surrounded by smooth muscle. The diameter of a capillary is less than the diameter of a red blood cell (which normally measures 7 micrometers in outer diameter), so as they pass through the capillaries, the red blood cells must deform in order to pass through them.
The small diameter of the capillaries provides a large surface area to promote the exchange of substances. In the different organs, the capillaries perform similar functions, but they specialize in one or the other:
- In the lungs , carbon dioxide is exchanged for oxygen
- In tissues , oxygen is exchanged for carbon dioxide and nutrients for waste products.
- In the Kidneys , waste products are released to be eliminated from the Body through urine
- In the intestine , nutrients are collected and waste products are eliminated, which are expelled with the feces.
Blood pressure
The arterial system is the portion of the circulatory system that has the highest pressure. Blood pressure varies between the peak produced during the cardiac contraction, which is called systolic pressure, and a minimum, or diastolic pressure between two contractions, when the heart expands and fills. This variation in pressure in the arteries produces the pulse, which can be seen in any artery, and reflects cardiac activity. The arteries, due to their elastic properties, also help the heart to pump blood , usually oxygenated, to the peripheral tissues.
Story
Among the ancient Greeks, the arteries were considered as “hollow tubes” responsible for the transport of air to the tissues, connected to the trachea. This interpretation is due to the fact that, in dead organisms, the arteries are empty, because all the blood passes into the venous system. In the Middle Ages, it was considered that the arteries carried a fluid, called ” spiritual blood ” or “vital spirit”, different from the content of the veins. This theory dates back to Galen. In the late medieval period, the Trachea , and the ligaments were also called “arteries.”
William Harvey described and popularized the modern concept of the circulatory system and the functions of arteries and veins in the 17th century . Although the Spaniard Miguel Servetus described the pulmonary circulation a quarter of a century before Harvey was born, he wrote it in a theology book (Christianismi Restitutio, published in 1553 ), which was considered heresy and led to the stake. Consequently, almost all copies of it were burned except for three, which were discovered decades later. Alexis Carrel at the beginning of the century XX was the first to describe the technique of suturing vessels and anastomosis, and performed many successful transplants Organs in animals, thus opening the way to modern vascular surgery.
Diseases of the arteries
- Arteriosclerosis
- Giant cell arteritis
- Aneurysm of aorta
References
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3. MOMMA, UR; Jean Hopkins, Charles William McLaughlin, Susan Johnson, Maryanna Quon Warner, David LaHart, Jill D. Wright (1993). Human Biology and Health. Englewood Cliffs, New Jersey: Prentice Hall. ISBN 0-13-981176-1.
4. Oxford English Dictionary.
5. Shakespeare, William. Hamlet Complete, Authoritative Text with Biographical and Historical Contexts, Critical History, and Essays from Five Contemporary Critical Perspectives. Boston: Bedford Books of St. Martins Press, 1994. pg. fifty.
6. Prives M. et al. Human anatomy. Volume I 4th ed. Editorial MIR. USSR 1981