Blood pressure is defined as ?the pressure of the blood against the walls of the arteries.? Blood pressure comes about as a result of two individual forces. The one force comes about due to the action of the heart as it pumps blood throughout the circulatory system as well as into the arteries. The other force is caused by the pressure of the arteries as they resist the flow of blood.

To explain blood pressure in as simple terms as possible, when the heart does its pumping action, blood is thereby forced through the largest of the arteries and from there to the smaller arteries and finally to the arterioles. It is the job of the arterioles to either expand (in other words, dilate) or contract, and by so doing cause a change to be brought about with regards to the resistance of the blood flow. This plays a role in both blood pressure and the quantity of blood flow. If contraction of the arterioles occurs, then blood flow resistance goes up which in turn decreases blood flow and increases the level of blood pressure. On the other hand, if the arterioles dilate then the opposite occurs (resistance of blood flow goes down, blood flow goes up and blood pressure decreases). Changes that occur in the inner center of the arterioles are vital when it comes to both regulating blood flow as well as making an adequate blood pressure determination. If the arterioles remain in a constricted state for a long period of time, high blood pressure (or hypertension) can take place.

Blood pressure is taken by way of a medical instrument known as a sphygmomanometer. Two measurements are derived from this simple blood pressure test that involves no pain, just pressure on the arm due to a rubber cuff that serves to compress a large artery to stop blood from flowing so measurements can be accurately taken. The two measurements are systolic pressure and diastolic pressure.

Systolic pressure (which is the higher number of the two) represents the blood flow pressure that is taken note of when the heart beats (or is contracting as it pumps blood) while diastolic pressure (the lower number) is the pressure of blood that is noted between individual heart beats (or the pressure when the heart takes time to relax between each heart beat).

Blood pressure is measured by mmHg (or millimeters of mercury). The more work it takes for the blood to flow through the arteries, the higher will both numbers be which is not good for the heath of the individual. The blood pressure measurement always gives the systolic pressure first and the diastolic pressure second, such as 120/80 (or 120 over 80) with 120 being the systolic blood pressure and 80 being the diastolic.