What really is hypertension? (here's an explanation from wikipedia)
Hypertension, also referred to as high blood pressure, HTN or HPN, is a medical condition in which the blood pressure is chronically elevated. In current usage, the word "hypertension" without a qualifier normally refers to systemic, arterial hypertension.Hypertension can be classified either essential (primary) or secondary. Essential hypertension indicates that no specific medical cause can be found to explain a patient's condition. Secondary hypertension indicates that the high blood pressure is a result of (i.e., secondary to) another condition, such as kidney disease or tumours (pheochromocytoma and paraganglioma). Persistent hypertension is one of the risk factors for strokes, heart attacks, heart failure and arterial aneurysm, and is a leading cause of chronic renal failure. Even moderate elevation of arterial blood pressure leads to shortened life expectancy. At severely high pressures, defined as mean arterial pressures 50% or more above average, a person can expect to live no more than a few years unless appropriately treated.
Causes of Hypertension
By definition, essential hypertension has no identifiable cause. However, several risk factors have been identified, including obesity, salt sensitivity, renin homeostasis, insulin resistance, genetics, and age.
The risk of hypertension is 5 times higher in the obese as compared to those of normal weight and up to two-thirds of cases can be attributed to excess weight. More than 85% of cases occur in those with a Body mass index greater than 25.
Sodium is an environmental factor that has received the greatest attention. Approximately one third of the essential hypertensive population is responsive to sodium intake.This is due to the fact that increasing amounts of salt in a person's bloodstream causes cells to release water (due to osmotic pressure) to equilibrate the concentration gradient between the cells and the bloodstream, thereby increasing the pressure within the blood vessel walls. The inceased Na+ stimulates ADH and thirst mechanisms, leading to a concentrated urine and the kidneys holding onto water along with the person increasing the intake of water. Also, the water movement between cells and the interstitium plays a minor role compared to this.
Hypertension is one of the most common complex disorders, with genetic heritability averaging 30%. Data supporting this view emerge from animal studies as well as in population studies in humans. Most of these studies support the concept that the inheritance is probably multifactorial or that a number of different genetic defects each have an elevated blood pressure as one of their phenotypic expressions.
More than 50 genes have been examined in association studies with hypertension, and the number is constantly growing.
Over time, the number of collagen fibers in artery and arteriole walls increases, making blood vessels stiffer. With the reduced elasticity comes a smaller cross-sectional area in systole, and so a raised mean arterial blood pressure.