Your Blood pressure (Hypertension) is the force by which your heart pushes blood through your arterial. It keeps blood moving through the body and allows blood to flow not only “downstream” but also “upstream” – as when taken from the feet to the heart. Blood pressure is highest in the arteries, especially in the heart. Therefore, when an artery is cut, blood flows to the surface, as if it had been expelled under intense pressure.

This blood is bright red because red blood cells carry a full load of oxygen from the heart on its way through the arteries. The push in the veins is much lower than in the arterial, so when the vein is cut blood tends to flow slowly from the injuries. This blood is dark purple because the blood now has carbon dioxide instead of oxygen. Blood pressure is in the lowest capillaries. These are so small that one red cell (which is so small that it takes almost 3200 to make an inch) can pass at a time.

Your doctor will measure your blood pressure by tying an airtight bag to your arm and pumping it up. This fills the bag with compressed air. When the pressure of the compressed air has constricted the bag just enough to stop the flow of blood in your hand, your doctor will know that the air pressure in the bag and your body’s blood pressure is the same. By measuring barometric pressure, he can tell what blood pressure is. The air pressure is measured at the height at which it pushes a “liquid metal” called mercury into the pipe. (See the article on compressing air.) Normal blood pressure is enough to send 120 to 150 millimeters of mercury (4Vi to 5 inches of Vi).

If a person’s blood pressure is much higher than that, it can be dangerous. There are several reasons why a person may have this, but the common reason is that his or her blood vessels are narrowed and not as large as they should be. The tiny the blood vessel, the harder the heart has to act to get enough blood. People with high blood pressure should get as much rest as possible so that their bodies do not need as much oxygen as when they are active. In addition, doctors give them special diets and medications that enlarge their blood vessels. High blood pressure usually only bothers elderly people. Children rarely suffer from it.