| Popis: |
The renin-angiotensin system (RAS), one of the oldest hormone systems, is a complex regulatory system with many identifiable actions. However, it may primarily be viewed as a powerful regulatory system for the conservation of salt and blood volume, and the preservation of an adequate blood pressure (BP). To circumvent the major threats of low blood volume and low BP, animals and our ancestors, with a diet relatively poor in sodium, needed powerful mechanisms for salt and water conservation, and their organisms relied heavily on the RAS. Many of the diverse actions of angiotensin II, the major end product of the RAS, can be viewed in a single conceptual framework, as serving to prevent life-threatening shrinkage of intravascular volume (rapid actions of angiotensin, in combination with the sympathetic nervous system), to help maintain volume homeostasis by minimizing the changes in arterial pressure and fluid volumes required to achieve sodium balance (prevention of salt-sensitivity), and to increase the efficiency of cardiovascular dynamics by promoting the growth of the heart and vessels, and sensitizing blood vessels to vasoconstrictor agents (slowest actions of angiotensin). Activation of the RAS is therefore a useful response in many demanding situations. However, an increased activity of the RAS, especially in combination with other cardiovascular risks factors, may lead to a cascade of deleterious effects. Many of these pathophysiological actions of angiotensin II may still be viewed as being homeostatic in principle, but harmful if carried to excess. |
