What happens inside your body if high blood pressure is not controlled?

You've probably heard that high blood pressure can contribute to heart disease, stroke and kidney failure. You may understand the risk better if you can visualize what's going on inside your body.
Simply put, when your blood pressure is high, your heart has to work harder than normal, which puts both the heart and the arteries under a greater strain.

Your heart

If you work hard lifting weights, your arm muscles will enlarge. In the same way, when the heart has to work harder for an extended time, it tends to enlarge. When your blood pressure is too high, your heart has to work progressively harder to pump enough blood and oxygen to your body's organs and tissues to meet their needs. The heart muscle stretches and thickens, and the heart stops functioning properly. A significantly enlarged heart has a hard time meeting the demands put on it and can fail.

Your arteries

Arteries are the vessels which carry blood throughout your body. When your blood pressure is too high, the arteries become scarred, hardened and less elastic. This occurs to some degree in all of us as we age, but elevated blood pressure speeds this process, which is called 'hardening of the arteries' or atherosclerosis.

Hardened or narrowed arteries may be unable to supply the amount of blood the body's organs need. If the organs don't get enough oxygen and nutrients, they can't function properly. There is also a risk that a blood clot may lodge in an artery narrowed by atherosclerosis, depriving part of the body of its normal blood supply.

If the arteries that supply blood to the heart become clogged, blood flow to parts of the heart is slowed. When one vessel is completely closed off, blood ceases to flow to part of the heart, and portions of the heart muscle are damaged. This is a heart attack.
Narrowing of the arteries may also cause chest pain, called angina pectoris. Narrowing of the arteries in the legs causes cramping and pain because the tissues are not getting enough oxygen.

Your brain

Stroke may be caused by the progressive narrowing of the blood vessels in the brain. When blood flow becomes inadequate, brain cells are robbed of oxygen, and they die. Narrowing of the vessels also leads to a situation where a blood clot cannot move through the arteries; it blocks the flow of blood and deprives the tissue beyond of oxygen. About 80% of strokes are caused by the blockage of an artery in the neck or brain.

People who suffer a stroke often are left with paralysis on one side of the body and loss of speech.
A stroke is an emergency just as is a heart attack. Its symptoms are:

Weakness, numbness or paralysis of the face, arm or leg – particularly on one side of the body

Difficulty speaking or understanding simple statements

Blurred or decreased vision in one or both eyes

Sudden, unexplainable and intense headache

Dizziness, loss of balance or loss of coordination, especially when combined with another symptom

Sudden nausea, fever and vomiting – distinguished from a viral illness by the speed of onset (minutes or hours vs. several days)

Brief loss of consciousness or period of decreased consciousness (fainting, confusion, convulsions or coma).

Your kidneys

High blood pressure can cause narrowing of the arteries in the kidneys – just as in other parts of your body – which can lead to kidney failure.
The primary function of the kidneys is to filter toxic chemicals from your blood. This process is accomplished in specialized structures inside the kidneys. The blood pressure of the vessels inside these filtering structures is critical for their proper functioning.

When the arteries are narrowed and thickened by high blood pressure, blood flow to the filtering structures is reduced, and they cease to function properly. The amount of fluid that the kidneys can filter is reduced, leading to kidney failure. Toxic materials build up in the body. People with kidney failure need to undergo dialysis – use of a machine as an artificial kidney – and may ultimately need a kidney transplant.

The kidney has its own feedback mechanism to maintain optimum blood pressure to assure its proper functioning. When this internal mechanism senses that blood pressure is too low, it tries to compensate by raising blood pressure, which begins a deadly spiral of higher and higher pressure.

Your eyes

As in other parts of your body, the blood vessels inside your eyes may also narrow and harden due to uncontrolled high blood pressure. This can cause clot formation and bleeding inside the eye, which leads to vision impairment and even blindness.