The kidneys are a pair of small, bean-shaped organs located towards the back of the torso and behind the lower ribs. The functions of the kidneys include filtering wastes from the blood, balancing the body's fluid content, and regulating blood pressure.
Normally, blood enters the kidneys through the renal arteries and then into smaller arterioles, which lead to individual filtering units, called glomeruli.
If a renal artery becomes narrowed due to injury or disease, a condition called renal stenosis, blood flow to the glomeruli will be reduced and the tiny arterioles will sense a decrease in blood pressure.
When this occurs, cells that line the arterioles release a hormone, called renin, into the blood stream. As renin enters the blood stream, it causes arterial constriction not only in the blood vessels of the kidneys, but all over the body--thus increasing the body's blood pressure.
Renovascular hypertension is a serious medical condition. If left untreated it can lead to organ damage, including damage to the heart and the lungs.