In more than 90% of cases, the cause of high blood pressure (hypertension) is unknown but several factors can increase your risk of developing the condition.
Where there is no specific cause, high blood pressure is referred to by doctors as primary or essential hypertension.
Factors that can raise your risk of developing primary hypertension include:
age – the risk of developing high blood pressure increases as you get older
a family history of high blood pressure (the condition seems to run in families)
being of African or Caribbean origin
a high amount of salt in your food
a lack of exercise
being overweight or obese
smoking
drinking large amounts of alcohol
Known causes
About 10% of high blood pressure cases are the result of an underlying condition or cause. These cases are referred to as secondary hypertension.
Source : www.nhs.uk/Conditions/Blood-pressure-%28high%29/Pages/Causes.aspx
How blood pressure is controlled
When the heart contracts, the blood inside the left ventricle is forced out into the aorta and arteries. The blood then enters small vessels with muscular walls, called arterioles. The tone in the muscular walls of the arterioles determines how relaxed or constricted they are. If narrowed, they resist flow.
Reduced flow of blood is detected in the brain, the kidneys and elsewhere. Nerve reflexes are stimulated and hormones are then produced. The heart is induced to beat more forcefully so that blood pressure is maintained at a higher level, to overcome the restricted flow through the arterioles. The achievement of good flow (now at high pressure) eases possible problems for function of the brain and kidneys.
These adjustments occur normally. However, in some people the adjustments become fixed and high blood pressure persists. These people have developed hypertension.
How blood pressure is measured
Hypertension can be mild, moderate or severe. Your blood pressure is naturally higher when you are exerting yourself, such as during physical exercise. It is only a concern if your blood pressure is high when you are at rest, because this means your heart is overworked and your arteries have extra stress in their walls.
Blood pressure readings are a combination of two measurements. These are:
Systolic – is the highest pressure against the arteries as the heart pumps. The normal systolic pressure is usually between 110 and 130mmHg.
Diastolic – is the pressure against the arteries as the heart relaxes and fills with blood. The normal diastolic pressure is usually between 70 and 80mmHg.
Source : www.betterhealth.vic.gov.au/bhcv2/bhcarticles.nsf/pages/hypertension_means_high_blood_pressure
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