The causes and mechanisms of hypertension

This sheet is about hypertension defined as essential or primary, that is, that which is not a consequence of other diseases This, on the other hand, is called secondary. Essential hypertension has no single cause, but is a consequence of several factors, among which there are genetic and environmental ones. The former involve the regulation of the renin-angiotensin-aldosterone system and that of the adrenergic system. Other functions conditioned by genes are the response of the vessels to mediators such as endothelin, the synthesis in the endothelium of molecules such as prostacyclins, and the tendency of the kidneys to eliminate sodium. Wanting to oversimplify the mechanism for the development of hypertension, it could be defined as an imbalance between the resistance that the vessels offer to blood flow and the cardiac output, which, in turn, depends on the systolic output and the rate of contraction of the heart. The mechanisms that maintain normal pressure act on precisely these functions. In particular, peripheral vessel resistances are regulated mainly by the sympathetic nervous system, which also modulates heart rate. Systolic output is affected by cardiac muscle contraction force and preload, and this, in turn, depends on volaemia. In addition, regulatory systems are divided into those with a short-term effect and those with a medium- and long-term effect. Among the former is precisely the sympathetic nervous system, which, based on information it receives from chemoreceptors and baroreceptors, modifies its tone. Among the medium-term modulating systems is the one called renin-angiotensin-aldosterone, which has less rapid response times. Among those that provide long-term regulation is renal function, on which blood volume depends. The development of hypertension can result from the disruption of each of these regulatory systems, but more often it depends on the disruption of more than one of them.

One factor that has always been invoked in the development of hypertension is excessive sodium intake. It causes an increase in blood volume and reflexes in peripheral vessel tone that increase blood pressure. On the other hand, clinical studies have shown that only in 20-30% of hypertensives is an appreciable reduction in blood pressure values achieved by decreasing salt intake. The endothelium plays an important role in protecting the vessels by releasing molecules, such as nitric oxide, prostacyclins, and EDRF (Endothelium-Derived Relaxing Factor), which result in vasodilation and substances that counteract thrombus formation. Factors related to lifestyle habits, such as smoking and diabetes, damage the endothelium, promoting inflammation that causes oxidative stress. This, in turn, alters the endothelium and limits its ability to release protective substances. Hypertension itself also subjects the endothelium to severe stress, which damages the endothelium itself, fueling a vicious cycle.

See also in the section Hypertension

Sources

  • M Volpe e S Sciarretta. Capitolo 45 L’ipertensione arteriosa. In: Manuale di malattie Cardiovascolari della Società Italiana di Cardiologia.
  • PK Whelton e coll. 2017 ACC/AHA/AAPA/ABC/ACPM/AGS/APhA/ASH/ASPC/NMA/PCNA Guideline for the Prevention, Detection, Evaluation, and Management of High Blood Pressure in Adults: Executive Summary. Hypertension. 2018;71:1269-1324.
  • LJ Visseren e coll. 2021 ESC Guidelines on cardiovascular disease prevention in clinical practice. European Heart Journal 2021; 00, 1-111.

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