The Heart Essay Research Paper CONTENTS3 — страница 3
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the starvation of oxygen of the heart, which also causes angina. The nerve factor – The arteries are supplied with nerves, which allow them to be controlled directly by the brain, especially the hypothalamus – an area at the centre of the brain which regulates the emotions. The brain controls the expanding and narrowing of the arteries when necessary. The pressures of modern life: aggression, hostility, never-ending deadlines, remorseless, competition, unrest, insecurity and so on, can trigger this control mechanism. When you become emotional, the chemicals that are released, such as adrenaline, noradrenaline, and serotonin, can cause a further constriction of the coronary arteries. The pituitary gland, a small gland at the base of the brain, under the control of the hypothalamus, can signal the adrenal glands to increase the production of stress hormones such as cortisol and adrenaline even further. Coronary spasm – Sudden constrictions of the muscle layer in an artery can cause platelets to stick together, temporarily restricting the flow of flow. This is known as coronary spasm. Platelets are minute particles in the blood, which play an essential role both in the clotting process and in repairing any damaged arterial walls. They tend to clump together more easily when the blood is full of chemicals released during arousal, such as cortisol and others. Coronary spasm causes the platelets to stick together and to the wall of the artery, while substances released by the platelets as they stick together further constrict the blood vessels. If the artery is already narrowed, this can have a devastating effect as it drastically reduces the blood flow. (Fig. 3 – Spasm in a coronary artery) When people are very tense, they usually overbreathe or hold their breath altogether. Shallow, irregular but rapid breathing washes out carbon dioxide from the system and the blood will become over-oxygenated. One might think that the more oxygen in the blood the better, but overloaded blood actually does not give up oxygen as easily, therefore the amount of oxygen available to the heart is reduced. Carbon dioxide is present in the blood in the form of carbonic acid, when there is a loss in carbonic acid, the blood becomes more basic, or alkaline, which leads to spasm of blood vessels, almost certainly in the brain but also in the heart. ATHEROSCLEROSIS The coronary arteries may be clogged with atherosclerotic plaques, thus narrowing the diameter. Plaques are usually collections of connection tissue, fats, and smooth muscle cells. The plaque project into the lumen, the passageway of the artery, and interfere with the flow of blood. In a normal artery, the smooth muscle cells are in the middle layer of the arterial wall; in atherosclerosis they migrate into the inner layer. The reason behind their migration could hold the answers to explain the existence of atherosclerosis. Two theories have been developed for the cause of atherosclerosis. The first theory was suggested by German pathologist Rudolf Virchow over 100 years ago. He proposed that the passage of fatty material into the arterial wall is the initial cause of atherosclerosis. The fatty material, especially cholesterol, acts as an irritant, and the arterial wall respond with an outpouring of cells, creating atherosclerotic plaque. The second theory was developed by Austrian pathologist Karl von Rokitansky in 1852. He suggested that atherosclerotic plaques are aftereffects of blood-clot organization (thrombosis). The clot adheres to the intima and is gradually converted to a mass of tissue, which evolves into a plaque. There are evidences to support the latter theory. It has been found that platelets and fibrin (a protein, the final product in thrombosis) are often found in atherosclerotic plaques, also found are cholesterol crystals and cells which are rich in lipid. The evidence suggests that thrombosis may play a role in atherosclerosis, and in the development of the more complicated atherosclerotic plaque. Though thrombosis may be important in initiating the plaque, an elevated blood lipid level may accelerate arterial narrowing. Plaque Inside the plaque is a yellow, porridge-like substance, consisting of blood lipids, cholesterol and triglycerides. These lipids are found in the bloodstream, they combine with specific proteins to form lipoproteins. All lipoprotein particles contain cholesterol, triglycerides, phospholipids, and proteins, but the proportion varies in different particles. Lipoproteins Lipoproteins all vary in size. The largest lipoproteins are called Chylomicra, and consist mostly of triglycerides. The next in size are the pre-beta-lipoproteins, then the beta lipoproteins.