Sodium intake: synthetic control responses
High sodium suppresses the antidiuretic system and activates the urinary system. As sodium intake increases, the initial sodium output is slightly slower than the amount absorbed.
The integration of various control systems regulating sodium and fluid excretion under normal conditions can be summarized by examining the homeostasis responses to progressive increases in sodium intake. into the. The kidneys have an excellent ability to combine their salt and water excretion into an absorption that can range from as low as 1/10 to 10 times higher than normal.
High sodium suppresses the antidiuretic system and activates the urinary system. As sodium intake increases, the initial sodium output is slightly slower than the amount absorbed. The delay leads to a small increase in sodium accumulation balance, with a slight increase in extracellular fluid volume. It is this small increase in extracellular fluid volume that triggers various mechanisms in the body to increase sodium excretion. These mechanisms include:
1. Activation of the low-pressure receptor reflex originating from the tension receptors of the right atrium and pulmonary blood vessels. Signals from tension receptors travel to the brain stem and there inhibit sympathetic nerve activity to the kidneys to reduce sodium reabsorption in the renal tubules.
This mechanism is most important during the first few hours - or perhaps the first day - after the salt and water intake has been greatly increased.
2. Inhibition of Angiotensin II formation, due to increased arterial pressure and dilated extracellular fluid volume, reduces renal tubular sodium reabsorption by eliminating the normal effect of Angiotensin II to increase reabsorption. sodium. In addition, Angiotensin II reduces aldosterone secretion, thereby reducing renal tubular sodium reabsorption.
3. Stimulates sodium excretion system, especially ANP, contributes to increased sodium excretion.
Therefore, the combination of activating the sodium diuretic system and inhibiting the sodium and water retention system leads to an increase in sodium excretion with an increase in sodium intake. The opposite changes occur when sodium intake falls below normal.
4. Minor arterial hypertension, caused by volumetric expansion, can occur with a large increase in sodium intake; This mechanism increases sodium excretion through pressure sodium diuresis. If neural, hormonal, and endocrine mechanisms are working effectively, a measurable increase in blood pressure may not occur even if sodium intake is elevated for several days. However, when high sodium intake is maintained for months or years, the kidneys can become damaged and less effective at excreting sodium, and it is necessary to increase blood pressure to maintain sodium balance through the elimination mechanism. pressure sodium urinary.