A healthy person's arteries are muscular and elastic. They stretch or contract when the heart pumps blood through them. The amount of stretching depends on the amount of force blood exerts. When your heart relaxes between beats, your blood pressure decreases. Systolic pressure tells the maximum amount of pressure on your arteries, while diastolic pressure tells the minimum pressure on your arteries.
Arterioles are smaller vessels that branch off from the arteries and regulate blood pressure.
If, for some reason, the arterioles are narrowed, it's harder for the blood to pass through them. When that happens, blood pressure rises and your heart works harder. High blood pressure affects one out of four Americans, with African-Americans being at highest risk. If your parents had high blood pressure you may be at greater risk as well. Gender is a factor, too, since men are more likely to develop hypertension than women.