When the heart beats, the force of the blood being pumped into the arteries create pressure. This pressure is what keeps the blood vessels inflated so the blood can keep moving through them.
Everyone knows what action a pump has on liquids, expecially those confined in closed vessels. Force is greatest nearest the pump, with less and less force being exerted on the vessel the further away from the pump one goes. In a closed system like the circulatory system, the blood must return to the heart. But, it has no pump to send it back, so it returns under far less pressure.
To determine if the heart is working normally, a blood pressure cuff is placed around the upper arm. It is inflated with air which is then slowly released as a technician listens through a stethoscope to the sounds the blood makes as it travels through the blood vessels. The first reading obtained is the higher systolic pressure of the freshly pumped, oxygenated blood as it leaves our heart and spreads out into the arteries. The second reading is the lower diastolic pressure of the oxygen-depleted blood returning to the heart.
Certain normal blood pressures are acceptable, depending upon your age, gender, and size. If you are above or below the numbers established to be the norm, it's usually a sign that something isn't right and needs to be addressed. If found to excessively high, it can usually be corrected by lower stress, better diet, medication, or increased physical activity.
The force of the blood against the walls of the blood vessels is known as blood pressure and depends on several factors such ads blood volume, blood vessel space, force of the heart beat and blood viscosity etc. Blood pressure varies considerably in different parts of the circulatory system. The maximum pressure is encountered in the aorta where it normally reaches to 140 mm of mercury. Then it gradually decreases in the arteries and arterioles, becoming lower in the capillaries and still lower in the veins.
The arterial blood pressure undergoes a rhythmic change reaching a maximum during ventricular systole when blood is pumped into the arteries and decreasing during ventricular diastole. The former is called systolic pressure and the latter, the diastolic pressure. The normal systolic pressure in man and in most other mammals ranges from about 120 to 140mm of mercury, whereas the diastolic pressure ranges from about 75 to 90 mm of mercury.