High Blood Pressure or Hypertension is a measure of the force your heart uses to pump blood throughout the body and the ability of your blood vessels to deal with that force.
If your vessels become narrowed, your heart has to pump harder to maintain circulation, thus exerting more pressure against the vessel walls. Eventually, this high pressure will increase your risk of developing heart disease and stroke

Causes

Some people develop high blood pressure during pregnancy or because of hormone imbalances or an illness such as kidney disease. But for most people, hypertension can't be traced to a single cause. A family history of hypertension doubles your chances of having it. High blood pressure is also more common in older people. Anyone who doesn't exercise, is overweight, drinks too much alcohol, or, in some cases, eats too much salt is at the risk of developing hypertension.
About 90% to 95% of hypertension cases, called primary, or essential hypertension, have no known cause. Primary hypertension may be influenced by factors such as genetic makeup, weight, or salt intake.
Secondary hypertension is hypertension that is caused by an underlying medical condition. Secondary hypertension is the name given to high blood pressure that has a specific cause, such as a thyroid or a kidney problem. The most common cause of secondary hypertension is kidney disease.

Symptoms

People with primary high blood pressure usually do not have any symptoms. Some people with hypertension experience occasional headaches; however, headaches are very common and can be caused by various other factors.

Most people with high blood pressure feel fine and only find out they have high blood pressure during a routine examination or a doctor visit for another problem.
 It is important to have your blood pressure checked, even if you don't have any symptoms. If untreated, slowly rising blood pressure can damage your brain, heart, kidneys, or arteries, and could lead to heart attacks, strokes, or kidney failure.

Treatment

Treatment for high blood pressure depends on the severity of the disease and whether you have other health problems, such as heart failure or diabetes, or you are pregnant.
If your blood pressure crosses the line into hypertension, your doctor will probably add medication to the treatment plan. However, you may be able to get results with less medication if you continue to follow the lifestyle changes intended to lower your blood pressure. Medication is generally prescribed right away for patients whose blood pressure is high normal but who also have heart failure, kidney failure, or diabetes.

Lifestyle changes that may reduce blood pressure include:

• Low salt diet
• reducing fat intake
• losing weight
• getting regular exercise
• Quit smoking.
• Reduce alcohol consumption.
• Get adequate dietary calcium.
• Control your stress.

If lifestyle changes do not lower your blood pressure enough, the doctor will begin drug therapy.

• Diuretics or "water pills" (thiazide, hydrochlorothiazide, chlorathalidone and indapamide) increase the elimination of salt and water through urination, thereby lessening blood volume and pressure.
• Beta-blockers (such as propranolol, atenolol, nadolol, pindolol and labetolol) lower blood pressure by reducing the amount of blood pumped by the heart.

• Angiotensin converting enzyme (ACE) inhibitors (captopril, enalapril and lisinopril) lower blood pressure by blocking the production of a hormone known as angiotensin, which increases blood pressure.

• Centrally acting drugs (clonidine and guanabenz) block the transmission of nerve impulses with the autonomic nervous system, which controls the involuntary action of the heart and blood vessels among other organs.

• Calcium-channel blockers (nifedipine, nicardipine, verapamil and diltiazem) relax blood-vessel walls, thereby lowering pressure.

• Vasodilators (hydralazine and minoxidil) relax the smooth muscle of the peripheral arteries, which causes them to dilate and so reduce the resistance to blood flow.

• Alpha-adrenergic antagonists can cause blood pressure to drop drastically when standing up. It helps in men with benign prostatic hyperplasia (big prostates), and is often used in men with both High Blood Pressure and Enlarged Prostates.

• Angiotensin II receptor antagonists -- similar to ACE inhibitors but with fewer side effects. This class of medicine should not be used in pregnancy since it may cause fetal abnormalities and death.
  Centrally acting -- most commonly used is Clonidine. Clonidine's biggest danger is that missing doses can cause severe "rebound" hypertension.