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This article aims to examine the normal blood pressure and explain in simple terms what is normal and why. It also provides a definition of high blood pressure and what the dangers of suffering from high blood pressure are. The article then goes onto outline low blood pressure, what it is and examples of the causes.

The systemic arterial blood pressure or more commonly just blood pressure is caused partly by contraction of the left ventricle in the heart, otherwise known as "systole" or "systolic blood pressure." The left ventricle pushes blood into the aorta, the walls of which then stretch. The wave of high pressure generated continues through the arterial system creating the systolic blood pressure which in an adult averages at 120mmHg (millimetres of mercury) in the major systemic arteries in adults. The pressure falls as blood is distributed through the arterial system and capillaries.

Once the left ventricle has ejected it's blood into the aorta it is relaxed and continues to fill with blood (diastole/diastolic). This creates a lower pressure in the systemic arteries which in an adult is on average 80-90mmolHg. The average adult blood pressure is therefore 120/90 mmolHg - this is usually referred to as 120 over 90 with the systolic reading being the first and top number and the diastolic being the bottom or second number.
Therefore in short the systolic reading represents the heart when it is contracting and pumping blood around the body and the diatolic represents the heart during it's relaxtion phase.

Abnormal blood pressures
Hypertension is an example of an abnormal blood pressure in which the pressure is too high. In general a guide to what is low or high is 100mmHg. If the diastolic pressure excedes this figure hypertension is suggested. Although blood pressure can rise with age chronic hypertension can damage organs and tissues especially the heart itself and blood vessels.
There are three types of hypertension:- essential hypertension; secondary hypertension and malignant hypertension.

1.Essential hypertension has no identifiable cause but it does result in sodium and water retention which in turn increases the blood pressure.
2.Secondary hypertension follows on from another pathology particularly chronic renal disease but also tumours of the pituitary and adrenal glands.
3.Malignant hypertension is a diatolic of over 130mmHg. It may be irreversible and can cause renal injury leading to kidney failure and death within

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