Blood pressure is the force or pressure that the blood exerts on the walls of the blood vessels. Systemic arterial blood pressure maintains the essential flow of blood into and out of the organs of the body. Keeping blood pressure within normal limits is very important. If it becomes too high,blood vessels can be damaged,causing clots or bleeding from sites of blood vessel rupture. If it falls too low,then blood flow through tissue beds may be inadequate. This is particularly dangerous for such essential organs as the heart,brain or kidneys.
The systemic arterial blood pressure,usually called simply arterial blood pressure,is the result of the discharge of blood from the left ventricle into the already full aorta.
Blood pressure varies according to the time of day,the posture,gender and age of the individual. Blood pressure falls at rest and during sleep. It increases with age.
Systolic and diastolic pressure. When the left ventricle contracts and pushes blood into the aorta,the pressure produced within the arterial system is called the systolic blood pressure.
When complete cardiac diastole occurs and the heart is resting following the ejection of blood,the pressure within the arteries is much lower and is called diastole blood pressure. The difference between systolic and diastolic blood pressures is the pulse pressure.
Elasticity of arterial walls. There is a considerable amount of elastic tissue in the arterial walls,especially in large arterials. Therefore,when the left ventricle ejects blood into the already full aorta,the aorta expands to accommodate it,and then recoils because of the elastic tissue in the wall. This pushes the blood forwards,into the systematic circulation. This detension and recoil occurs through out the arterial system. During cardiac diastole the elastic recoils of the arteries maintains the diastolic pressure.
