The Cardiovascular System
The cardiovascular system delivers oxygen, hormones, nutrients, and white blood cells throughout the body by circulating blood. The heart, a fist-sized series of muscles that is nothing more than a pump, powers everything. As we alerted you in the previous chapter, just like any mechanical device, the heart has a finite lifespan—80 years, more or less, which is pretty good for any pump. Depending on how hard and how fast it is required to run, under what conditions it is forced to operate, and how it is cared for, it can last significantly shorter or longer than its advertised specifications. Unlike most other pumps, the heart is subject to both automatic and manual operation. It can be speeded up or slowed down at will, just by thinking about an image of a South Pacific beach, an impending deadline, or an attractive classmate. The heart is also capable of independent action as it continues to beat steadily, thumping away when you are awake or asleep.
As you learned earlier, one immediate response to a stressor is accelerated heart rate and increased blood pressure. To accelerate the cardiovascular system, the body cranks up the sympathetic nervous system to release epinephrine and norepinephrine and causes the adrenal glands to secrete more glucocorticoids and mineralocorticoids. In addition, the thyroid gland gets into the act, teaming up to help increase blood pressure and heart rate. At the same time, the kidneys decrease urine production, thereby increasing the blood volume. During stress reactions, blood thickens and clots tend to form more easily, resulting in increased likelihood of strokes.
When the stressful situation is over, the parasympathetic system is activated to bring the metabolic rate down through lowering the heart rate, dilating blood vessels, and returning more blood to the gut. Yet, when you experience chronic stress, the cardiovascular system is kept working overtime without regular breaks, creating a condition of hypertension, or chronically elevated blood pressure. It is estimated that 15% to 20% of the adult population is faced with this disease.
Elevated blood pressure is harmful to the heart and the blood vessels in a number of ways. When blood is returning to your heart with greater force, it makes a stronger landing on the muscle, causing a thickening and enlargement over time. Once this occurs, the heart requires more blood than the coronary arteries can supply.
The connecting places where large vessels branch into smaller vessels bear the brunt of the increased blood pressure. Repeated crushing against these spots causes wear and tear, eventually leading to tissue damage. Once the smooth lining of the vessel begins to form little craters of damage, inflammation results. These craters become a gathering site for circulating platelets, fats, cholesterol, glucose, and other material in the body. Over time, the blood vessels will become fragile and clotted, leading to arteriosclerosis (heart disease). As the vessels become further infused with plaque, calcium, and other fatty acids, they harden and lose elasticity. Coronary events (as heart attacks are called) may soon follow.
High blood pressure combined with arteriosclerosis (plaque/cholesterol) is very dangerous. Greater force is pushing blood through pipes that are on the verge of rupture. When the rupture occurs in the brain, it is a cerebral hemorrhage leading to a stroke or apoplexy. When a coronary artery ruptures, a heart attack or a myocardial infarction occurs, because a part of the heart dies from lack of oxygen. Scientists have learned that many factors contribute to the development of arteriosclerosis and hypertension. High saturated fats in diet provide a significant source of bad cholesterol. Lack of exercise, and little time for relaxation, further increase the allostatic load on the body. Other contributing factors include smoking, heredity, and diabetes. Yet more than anything else it is often psychological factors that predispose some people to have fatal heart attacks: half of all such victims did not have elevated cholesterol but rather manifested certain behavioral and attitudinal traits that are associated with chronic stress (Underwood, 2005).
Let’s review to this point: the heart is a pump; the arteries and veins are pipes. Stress increases the fluid pressure within this circulatory system, over and over, straining the walls, the valves and seals. Stressed blood is thicker with platelets that are needed to provide emergency clotting and with fatty nutrients needed for energy. This leaves behind deposits (called plaque) in its wake, creating weakening in the linings, inflammation, and higher concentrations of cholesterol. Where does all this lead? Stress increases the risk of heart disease, stroke, and high blood pressure. No matter how much you control your diet or take drugs, stress leaves behind a combination of chemicals that clog your arteries and slowly restrict the functioning of the pipe system. That means your heart now has to work even harder to deliver the necessary oxygen and nutrients to other areas. And what do you think that does to its longevity?
Perhaps you recognize that this is all very much like a sump pump located in the basement of a building. The pump is activated only when the water level rises to a predetermined level, then it whirrs into operation until the level is brought down, returning to a resting state. When such a pump malfunctions, or when the water keeps flooding in faster than the pump can operate, the mechanical parts wear out—stress fractures its weakest parts. This is what happens to your heart during prolonged stress.
Sumber : Kottler, Jeffrey A. 2011. Stress Management & Prevention. New York : Routledge
Published at : Updated