When the heart contracts, the blood is pumped from your heart through the arteries into your body. The blood puts a force against the blood vessel (or artery) walls. This pressure is known as systolic blood pressure. When the heart is relaxing before it contracts again, the existing pressure in the arteries is known as the diastolic blood pressure. Your blood pressure is a reading of this pressure. When that reading goes above a certain point, it is called high blood pressure or 'hypertension'. When you have high blood pressure, it is partly because your blood vessels become narrower, and more constricted forcing your heart to pump harder to move blood through your body. These changes cause the blood to press on the artery vessels walls with greater force.

Why is high blood pressure dangerous?
High blood pressure is also called the " silent killer " because it usually has no symptoms. If not controlled over time, high blood pressure can affect not only your heart and blood vessels but also other organs, making them function not as well as they should.

The effects of uncontrolled high blood pressure include:

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  Stroke
  High blood pressure is the most important risk factor for stroke. High blood pressure can cause a break in a weakened blood vessel in the brain. This can cause bleeding in the brain, which is a stroke. If a blood clot blocks a narrowed blood vessel, it can also cause another type of stroke.
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  Impaired vision
  Blood vessels in the eye can, in time, burst or bleed due to high blood pressure. Vision can become blurred or impaired which can result in blindness.
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  Kidney damage
  Kidneys are the marvellous filters of the body. The kidneys filter wastes from our bodies. Over time, high blood pressure can narrow and thicken the blood vessels of the kidneys. Thus, the kidneys cannot do their job well, and wastes build up in the blood.
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  Heart attack
  High blood pressure is a major risk factor for heart attacks. If the heart cannot get enough oxygen because of narrowed or hardened arteries, chest pain (angina) can occur. If the flow of blood is blocked, a heart attack results.
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  Congestive heart failure
  High blood pressure is the number one risk factor for congestive heart failure, a serious condition where, the heart gets so tired of beating harder and harder that it is not able to pump enough blood to meet the body's needs.
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  Vascular dementia
  Overtime, the brain gets less and less blood supply and persons intelligent faculties go down.
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  Peripheral blood vessel disease
  The circulation to the feet may get hampered which may give rise to pain and other problems and even at times gangrene.
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  Aortic aneurysm
  The first big artery where the heart pumps all the blood, over time, at a certain location, may start ballooning; if this balloon bursts it can be life threatening.