Hypertension, Hypotension, and Arteriosclerosis Help
Introduction to Hypertension, Hypotension, and Arteriosclerosis
We have been talking about the normal blood pressure, which has an average or set-point level of about 120/80 mmHg. The normal BP can rise to an upper limit of about 140/90 mmHg. And it can fall down to a lower limit of about 100/60 mmHg. The distance between these upper and lower normal readings creates the normal range for blood pressure, a condition that can technically be called normotension ( NOR -moh- TEN -shun). We use this term because blood “pressure” represents the amount of tension exerted against the blood. Figure 16.5 (A) illustrates a state of normotension: that is, a state of relative constancy or homeostasis of blood pressure within its normal range.
Unfortunately, however, blood pressure doesn’t always remain within its normal range. Say that a lumberjack accidentally cuts his brachial artery with a chainsaw while felling a large oak tree. The blood spurts out in hot red jets, resulting in a severe and possibly fatal hemorrhage ( HEM -uh-rij) – a “bursting out” (-orrhage) of “blood” (hem). When so much blood is lost, there isn’t much blood left to press against the arterial wall. Thus, blood pressure steeply declines. It may even reach a state of hypotension ( HIGH -poh- TEN -shun). Hypotension is a condition of “below normal or deficient” (hypo-) blood “pressure” ( tens ). Specifically, hypotension is a blood pressure significantly less than 100/60 mmHg (Figure 16.5, B).
At the opposite extreme lies hypertension ( HIGH -per- TEN -shun) – an “excessive or above normal” (hyper-) blood pressure. Hypertension is a blood pressure significantly above the upper normal limit of approximately 140/90 mmHg (Figure 16.5, C).
“So what if a person has hypotension or hypertension?” a skeptic might inquire. With hypotension, the person may easily faint. And if the condition is severe, there may be circulatory shock or coma, due to a lack of blood pressure pushing blood up to feed the brain. In the case of hypertension, the chronically above-normal pressure may overstretch and thin out the walls of arteries, creating aneurysms ( AN -yuh- riz -ums). Aneurysms are abnormally “widened up” arteries, which are highly susceptible to being ruptured. And when an aneurysm ruptures, there may be a large amount of internal bleeding. Persons suffering a stroke, or cerebrovascular (seh- REE -broh- VAS -kyoo-lar) accident, for instance, may well have experienced a ruptured aneurysm of their cerebral blood vessels covering the brain. Whatever particular body functions the oxygen-and-blood-deprived brain area carried out, are then partially or totally lost.
Closely related to hypertension is the condition called arteriosclerosis (ar- teer -ee-oh-sklair- OH -sis). Arteriosclerosis is “an abnormal condition of” (-osis) “hardening” (scler) of the walls of an “artery” (arteri).
There is a positive feedback relationship between arteriosclerosis and hypertension. You may remember (Chapter 14) that a negative feedback system removes or corrects a particular change. It thus tends to re-establish or maintain a state of Biological Order.
Positive feedback, however, is a system that magnifies or accelerates change in some particular direction. Whatever is happening already, positive feedback makes it even more extreme, or worse. Thus, positive feedback is sometimes referred to as a vicious cycle. It magnifies or accelerates changes that often veer out of control, thereby promoting Biological Disorder.
Consider hypertension and arteriosclerosis (Figure 16.6). When the BP is consistently elevated above its normal range, then it tends to damage the elastic fibers within the arterial walls. [ Study suggestion: Picture a garden hose with an adjustable nozzle at the end. It is attached to a faucet that is left turned on all summer, with the nozzle closed. What will eventually happen to the garden hose?] When the elastic fibers are damaged, the arterial wall gets stiffer, and when the arterial wall gets stiffer, the BP goes up even more. This makes the hypertension worse. And as the hypertension worsens, the elevated pressure damages the elastic fibers to an even greater extent.
Hence, there is a positive feedback relationship (vicious cycle) between hypertension and arteriosclerosis. The worse the hypertension gets, the more the arterial wall hardens, and the more the arterial wall hardens, the worse the hypertension gets. Adding to the damage, calcium ions are pushed out of the bloodstream by the high BP, becoming embedded in the arterial wall. So the once soft, pliable, garden hose-like normal artery progressively transforms into a rock-hard, stiff, calcified ( KAL -sih- feyed ) tube that more resembles a heavily limed-up lead water pipe!
Practice problems for these concepts can be found at: Blood And The Circulatory System Test
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