Regulation of sodium in your body requires tight controls of the amounts of fluid in your body. Your body has a number of "sensors" that detect your overall sodium level, many of which are in the kidneys. When your sodium levels are too high, hormones can set off a number of reactions that cause your body to retain fluid. The reverse is true when sodium levels are low, so your body fluids are not too diluted because sodium is required to maintain balance in your cells.
Renin
Three major hormones are involved in managing sodium levels in the kidneys: renin, angiotensin and aldosterone. Together they make the renin-angiotensin-aldosterone system, which is a chainlike reaction to managing sodium intake and release. The kidneys produce renin, an enzyme that signals the formation of angiotensin in the body. Renin also prevents sodium from reaching the distal tubules in the kidneys. When sodium reaches these tubules, the kidneys signal the body to release sodium and fluids. By preventing sodium from reaching the tubules, your body will hold on to sodium.
Angiotensin
When the kidneys release renin, it acts as a puzzle piece, meeting with angiotensinogen. When the two combine, they form angiotensin I. Next, angiotensin I is converted into angiotensin II from enzymes present in the lungs. This hormone has several actions, including stimulating the uptake of sodium and fluid in the body and the release of the next hormone that affects your kidneys: aldosterone.
Aldosterone
Aldosterone is the major regulator of sodium in your kidneys. This hormone is produced in your adrenal glands, which are located just above the kidneys. When stimulated by angiotensin-aldosterone system, aldosterone opens the channels in the kidneys, telling them to absorb sodium. This hormone helps to "save sodium," increasing the concentration of sodium in your blood if your blood is becoming too diluted.
Atrial Natriuretic Peptide
Atrial natriuretic peptide, also known as ANP, is another hormone responsible for regulating sodium levels in the body. This hormone is present in the cells of the heart and acts as a measurement of your overall blood volume. If the plasma walls become distended because your blood volume increases, ANP is released. ANP signals your kidneys to increase the rate of fluid release and minimizes how much sodium was absorbed. In this manner, ANP works in opposition to the renin-angiotensin-aldosteron system because it releases sodium.
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