Blood pressure regulation: the role of the renal-humoral system
The renal-fluid system in blood pressure control is a fundamental mechanism for long-term blood pressure control. However, through the stages of evolution, many modifications have been made to make this system more precise in performing its role.
The sympathetic nervous system plays a major role in the immediate regulation of blood pressure, through the nervous system's influence on the total vascular resistance of the peripheral circulation, and the carrying capacity and pumping capacity of the heart.
However, there are also powerful mechanisms for regulating arterial blood pressure week to week and month to month. The long-term control of arterial blood pressure is inextricably linked with body fluid equilibrium, which is determined by the balance between fluid intake and output. For long-term survival, fluid intake and output must be perfectly balanced, a task performed by neuroendocrine and endocrine control and by the renal control system, which regulates salt excretion and secretion. country.
This system is slow but powerful and is described as follows: if blood volume is increased and capillary capacity is constant, then blood pressure will increase. High blood pressure causes the kidneys to excrete a large amount of fluid, so blood pressure returns to normal.
In the phylogenetic and evolutionary history of animals, the humoral nervous system that regulates blood pressure has existed since the beginning. It is fully functional even in the most primitive vertebrates such as hagfish. These animals have low blood pressure, only 8-14 mm Hg, and blood pressure increases almost directly in proportion to blood volume. Hagfish continuously drink seawater, which is then absorbed into the bloodstream, increasing blood volume and blood pressure. However, when blood pressure gets too high, the kidneys simply excrete the excess volume into the urine and lower blood pressure. When blood pressure is low, the kidneys excrete less fluid than they take in. Then, due to continued water intake, the extracellular fluid volume, blood volume, and blood pressure increased again.
This primitive mechanism of blood pressure regulation persists through the ages, from hagfish to humans, but humans are more sensitive to blood pressure changes than hagfish. Indeed, an increase in arterial blood pressure of just a few mm Hg can double the amount of water excreted by the kidneys, a phenomenon known as pressure diuresis, as well as double the amount of salt excreted. This is called pressure hypernatremia.
In humans, like hagfish, the renal-fluid system in blood pressure control is a fundamental mechanism for long-term blood pressure control. However, through the stages of evolution, many modifications have been made to make this system more precise in performing its role. A particularly important reinforcement is the renin-angiotensin mechanism.