Blood Pressure
Blood Pressure, pressure of circulating blood against the walls of the arteries (blood vessels that carry blood from the heart to the rest of the body). Blood pressure is an important indicator of the health of the circulatory system . Any condition that dilates or contracts the arteries or affects their elasticity, or any disease of the heart that interferes with its pumping power, affects blood pressure. In a healthy human being, blood pressure remains within a certain average range. The complex nervous system mechanisms that balance and coordinate the activity of the heart and arterial muscles permit great local variation in the rate of blood flow without disturbing the general blood pressure. Hemoglobin , the iron-protein compound that gives blood its red color, also plays a role in regulating local variation in blood pressure. Hemoglobin carries nitric oxide, a gas that relaxes the blood vessel walls. Hemoglobin controls the expansion and contraction of blood vessels, and thus