Hypertension continued

hours with no lasting effects, but may be a warning of an impending, more serious stroke.

Treatment of hypertension varies and may include exercising regularly, controlling 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 urinary excretion of sodium and water, reducing the volume of body fluids. Sympathetic inhibitors block the synthesis of neurotransmit-ters, such as norepinephrine, or block receptor sites of effector cells. Table 15B describes how drugs that treat hypertension work. ■

Risk Factors for Stroke

Risk Factors for Stroke

Alcohol consumption Diabetes

Elevated serum cholesterol

Family history of cardiovascular disease



Transient ischemic attacks

Drugs to Treat Hypertension

Type of Drug

Mechanism of Action

Angiotensin-converting enzyme (ACE) inhibitors

Block formation of angiotensin II, preventing vasoconstriction

Beta blockers

Lower heart rate

Calcium channel blockers

Dilate blood vessels by keeping calcium ions out of muscle cells in vessel walls


Increase urine output, lowering blood volume

Respiratory movements also move venous blood. During inspiration, the pressure within the thoracic cavity is reduced as the diaphragm contracts and the rib cage moves upward and outward. At the same time, the pressure within the abdominal cavity is increased as the diaphragm presses downward on the abdominal viscera. Consequently, blood is squeezed out of the abdominal veins and forced into thoracic veins. During exercise, these respiratory movements act with skeletal muscle contractions to increase return of venous blood to the heart.

The veins also provide a blood reservoir that can adapt its capacity to changes in blood volume (see fig. 15.33). If some blood is lost and blood pressure falls, vein constriction (venoconstriction) can force blood out of this reservoir, returning venous blood to the heart. By maintaining venous return, venoconstriction helps to maintain blood pressure.

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