Hypertension, or high blood pressure, is persistently elevated arterial pressure. It is one of the more common diseases of the cardiovascular system.

High blood pressure with unknown cause is called essential (also primary or idiopathic) hypertension. Elevated pressure related to another problem, such as arteriosclerosis or kidney disease, is secondary hypertension.

Arteriosclerosis is accompanied by decreased elasticity of the arterial walls and narrowed vessel lumens, which contribute to increased blood pressure. Kidney diseases often produce changes that interfere with blood flow to kidney cells. In response, the affected tissues may release an enzyme called renin what leads to the production of angiotensis II, a powerful vasoconstrictor that increases peripheral resistance in the arterial system, raising arterial pressure. Angiotensin II also stimulates the adrenal cortex to release aldosterone, which stimulates the kidneys to retain sodium ions and water. The resulting increase in blood volume contributes to increased blood pressure.

Normally, this mechanism ensures that a decrease in blood flow to the kidneys is followed by an increase in arterial pressure, which, in turn, restores blood flow to the kidneys. If the decreased blood flow is the result of disease, such as atherosclerosis, the mechanism may cause high blood pressure and promote further deterioration of the arterial system.

In some individuals, high sodium intake leads to vasoconstriction, raising blood pressure. Obesity also is a risk factor for hypertension because it tends to increase peripheral resistance. Psychological stress, which activates sympathetic nerve impulses that cause generalized vasoconstriction, may also lead to hypertension. Yet another cause of hypertension may be an inability of endothelium to respond to a relaxing factor, leading to vasoconstriction.

Hypertension is called a "silent killer" because it may not have direct symptoms yet can set the stage for serious cardiovascular complications. For example, as the left ventricle works overtime to pump enough blood, the myocardium thickens, enlarging the heart. If the coronary blood vessels cannot support this overgrowth, parts of the heart muscle die and become replaced with fibrous tissue. Eventually, the enlarged and weakened heart dies.

Hypertension also contributes to the development of atherosclerosis. As arteries accumulate plaque, a coronary thrombosis or a coronary embolism may occur. Similar changes in the arteries of the brain increase the chances of a cerebral vascular accident (CVA), or stroke, due to a cerebral thrombosis, embolism, or hemorrhage.

When an embolus or hemorrhage causes a stroke, paralysis and other functional losses appear suddenly. A thrombus-caused stroke is slower. It may begin with clumsiness, progress to partial visual loss, then affect speech. One arm becomes paralyzed, then a day later, perhaps an entire side of the body is affected.

A transient ischemic attach (TIA, or ministroke") is a temporary block in a small artery. Symptoms include difficulty in speaking or understanding speech; numbness or weakness in the face, upper limb, lower limb, or one side; dizziness; falling; an unsteady gait; blurred vision; or blindness. These symptoms typically resolve within 24 hours with no lasting effects but may be a warning of an impending, more serious stroke.

Treatment of hypertension varies among patients and may include exercising regularly, controlling body weight, reducing stress, and limiting the diet to foods that are low in sodium. Drugs, such as diuretics and/or inhibitors of sympathetic nerve activity, may help control blood pressure. Diuretics increase urinay excretion of sodium and water, reducing the volume of body fluids. Sympathetic inhibitors block the synthesis of neurotransmitters, such as norepinephrine, or block receptor sites of effector cells.