An irony is continuously happening within the body. We all have an idea of how important the role of sodium when talking about fluid and electrolyte balance but receptors that specifically monitor the levels of sodium in body fluids have yet to be found.
The regulation of sodium and water balance is linked to the volume and pressure of the blood. Furthermore, it also involves a wide variety of hormonal and neural controls. The reabsorption of sodium does not exhibit a maximum and it is amazing to note that all sodium found in the urinary filtrate can be reabsorbed.
Influence of Aldosterone
When talking about the renal regulation of the concentrations of sodium ion in the ECF, the hormone aldosterone has the most influence. Regardless of the presence or absence of aldosterone, close to about 65% of the sodium present in the renal filtrate is being reabsorbed in the proximal tubules and another portion of sodium, about 25% is reclaimed in the Loop of Henle.
An increase in the concentrations of Aldosterone influences the distal convoluted tubules and the collecting ducts to reabsorb the remaining sodium. As sodium is being reabsorbed, water also follows sodium hence aldosterone not only promotes sodium but also constitutes to water retention. Conversely, when there is inhibition in the release of aldosterone, no sodium is reabsorbed beyond the distal tubule.
Influence of Atrial Natriuretic Peptide
It is easy to understand the action of ANP or atrial natriuretic peptide. It inhibits all activities that promote vasoconstriction and also sodium and water retention. With this action, it reduces blood volume and blood pressure.
A vital question to answer now is, where does atrial natriuertic peptide come from? To answer that, you just merely have to look at the first word of ANP. The word atrial signifies that this hormone comes from the heart. As blood pressure moves up, some cells of the heart atria react by releasing ANP. ANP is a potent diuretic and also has natriuretic effects or the ability to excrete salts. By having the ability to inhibit reabsorption of sodium and water, it promotes their excretion. It also has bearing on the suppression of renin, aldosterone and ADH. ANP is able to reduce blood pressure by relaxing smooth muscles, thus causing vasodilation.
Influences of Other Hormones
A close relative of aldosterone, when talking about function, is estrogen. It has the same function of aldosterone which is to enhance the reabsorption of sodium chloride in the tubules. Like what you have read time and again, water follows wherever sodium goes so many women retain fluid especially during menstrual cycle because their estrogen levels rise. This also holds true when talking about edema in pregnant women. On the contrary, progesterone has the opposite effect of estrogen. It blocks the effect of aldosterone in the tubules, thereby limiting and inhibiting the reuptake of sodium.
Hydrocortisol and cortisol are examples of glucocorticoids that enhance the reabsorption of sodium in the tubules. Their presence also increases GFR that may sometimes mask the effects they bring to the tubules.