Hypertension is a consequence of many diseases. Hemodynamically, blood pressure is a function of the amount of blood pumped by the heart and the ease with which the blood flows through the peripheral vasculature (i.e., resistance to blood flow by peripheral blood vessels). Diseases of components of the central and peripheral nervous systems, which regulate blood pressure and abnormalities of the hormonal system, and diseases of the kidney and peripheral vascular network, which affect blood volume, can create a hypertensive state in humans. Hypertension is generally defined as mild when the diastolic pressure is between 90 and 104 mm Hg, moderate when it is 105 to 114 mm Hg, and severe when it is above 115 mm Hg. It is estimated that about 15% of the adult population in the United States (about 40 million) are hypertensive.
Primary (essential) hypertension is the most common form of hypertension. Although advances have been made in the identification and control of primary hypertension, the etiology of this form of hypertension has not yet been resolved. Renal hypertension can be created by experimentally causing renal artery stenosis in animals. Renal artery stenosis also may occur in pathological conditions of the kidney, such as nephritis, renal artery thrombosis, renal artery infarctions, or other conditions that restrict blood flow through the renal artery. Hypertension also may originate from pathological states in the CNS, such as malignancies. Tumors in the adrenal medulla that cause release of large amounts of catecholamines create a hypertensive condition known as pheochromocytoma. Excessive secretion of aldo-sterone by the adrenal cortex, often because of adenomas, also produces hypertensive disorders.
Arterial blood pressure is regulated by several physiological factors, such as heart rate, stroke volume, peripheral vascular network resistance, blood vessel elasticity, blood volume, and viscosity of blood. Endogenous chemicals also play an important part in the regulation of arterial blood pressure. The peripheral vascular system is influenced greatly by the sympathetic-parasympathetic balance of the autonomic nervous system, the control of which originates in the CNS. Enhanced adrenergic activity is a principal contributor to primary (essential) hypertension.
Therapy using antihypertensive agents evolved rapidly between 1950 and 1960. During that time, several drugs for the treatment and control of hypertensive disease were discovered. Despite the many years of experience, treatment remains empiric because the etiology of the principal form of hypertension, primary hypertension, is unknown. The first drugs used to produce symptomatic relief of hypertension were a-adrenergic blocking agents. These drugs had limitations because their duration of action was far too short and side effects precluded long-term therapy. Contemporary therapy of primary hypertension uses one of several drug classes as the first course. These drugs may be diuretics to reduce blood volume, inhibitors of the renin-angiotensin system (ACE inhibitors, Chapter 18), and agents that reduce peripheral vascular resistance (e.g., calcium channel blockers, vasodilators, and sympathetic nervous system depressants). The antihypertensive drug classes discussed in this section include endothelin receptor antagonists, sympathetic nervous system depressants, and vasodilators acting on smooth muscle. Calcium channel blockers and other vasodilators are included in previous discussions in this chapter. Diuretics and renin angiotensin system are discussed in Chapter 18.
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Your heart pumps blood throughout your body using a network of tubing called arteries and capillaries which return the blood back to your heart via your veins. Blood pressure is the force of the blood pushing against the walls of your arteries as your heart beats.Learn more...