BLOOD PRESSURE AND YOUR PUMP-AND-PIPES SYSTEM

The pressure in any pump-pipes system can shift with changes in any one or a combination of three things: pumping intensity, rate, and output; fluid volume of the system; and resistance on the pipes. Here’s how these factors correspond to the pressure of blood in your own pump-and-pipes system.
Pumping intensity, rate, and outputThe more intense or rapid the heartbeat, the greater the volume of blood pumped out of the heart with each beat (known as cardiac output) and the higher the blood pressure throughout the system. Stress or exercise, for example, prompts the adrenal glands to secrete hormones that speed up heart rate and cardiac output. This in turn elevates blood pressure.
Fluid volumeThe more blood in the system, the greater the pressure against the blood vessel walls. Blood volume increases – and blood pressure rises – when sodium levels increase and cause water to be retained by the body. This results from dietary indiscretions and mineral imbalances.
Resistance on the pipesAs blood flows through the vessels, it encounters friction or a phenomenon known as peripheral resistance (because the greatest friction is in the peripheral arterioles, away from the heart). Three things contribute to peripheral resistance. One is blood viscosity, or thickness. The thicker the blood, the less easily it flows and the higher the blood pressure. Excess fat in the diet may contribute to increased blood viscosity. Another contributor to peripheral resistance is total blood vessel length – the longer the length, the greater the resistance. Every extra pound on your body requires additional blood vessels to sustain it, and this is one reason why weight gain is associated with increases in blood pressure.The third and perhaps most significant cause of peripheral resistance and increased blood pressure is decreased diameter and responsiveness of the arteries and arterioles. The muscular walls of your arteries and arterioles enable them to constrict and expand to divert blood to various areas, depending on your body’s needs. When they constrict and become smaller – decreasing the diameter of the pipes – blood pressure goes up. The arteries and arterioles constrict in response to hormones and other chemical messengers associated with stress, exercise, and other factors, as well as to mineral imbalances at the cellular level. In addition, arteriosclerosis (stiffening and thickening of the arteries) and atherosclerosis (buildup of plaque in the arteries) also decrease the diameter and flexibility of the arteries, thus contributing to peripheral resistance and higher blood pressure.*12/313/5*