Blood pressure set point.

This paper has two main purposes: A) to emphasize the role of the kidney in setting peripheral resistance, thus arterial blood pressure and flow distribution since birth to full grown; and B) to bring attention to the role that changes in pulse pressure and pulse velocity may have in the genesis of aging hypertension. A) According to the tonus regulation at basal steady conditions, the arterial system may be divided into three areas: I) the skin, in which the vascular tonus is regulated by heat; II) the kidney, whose vessels are regulated by glomerulo-tubular balance; and III) the rest of organs and tissues of the body, whose tonus is regulated according to the oxygen the cell needs to maintain its energetic equilibrium (ATP/ADP relationship). As area III has the higher flow and lowest equivalent resistance, the kidney is--hemodynamically--the organ that sets arterial blood pressure during life. Nevertheless, since birth to full grown, the kidney must progressively adjust the peripheral resistance of area III, in order to allow arterial blood pressure and renal distribution to match glomerular filtration with the increasing body metabolism. The tool that the kidney uses to adjust resistance of area III, thence arterial blood pressure and blood distribution, is the renin-angiotensin system. B) Aging decreases vascular distensibility. Lower distensibility of the arterial tree results in a progressive increase in amplitude and velocity of the pulse wave, then in its potency. Small resistance vessels must increase Bayliss response in order to reduce pulse impact on the precapillarial arteries. Structural changes in the resistance vessels, as well as in preglomerular arteries, should establish a feed-back mechanism responsible for the evolution of arterial blood pressure.