What is the role of kidneys in balancing body fluids?

Your body is made up of about 60 percent water, and keeping that fluid in balance is vital for every cell, tissue, and organ. The kidneys play a central role in this process. They constantly monitor and adjust the amount of fluid in your body by controlling how much water and salt are excreted in the urine.

When you drink more water than your body needs, your kidneys respond by producing more urine to get rid of the excess. When you are dehydrated, they conserve water by concentrating the urine and producing less of it. This automatic adjustment helps maintain the right fluid levels in your blood and tissues.

In addition to water, your kidneys also regulate electrolytes—minerals like sodium, potassium, and calcium—that are dissolved in body fluids. These electrolytes help control everything from nerve signals to muscle contractions. Too much or too little of any of them can disrupt important body functions. The kidneys carefully balance these levels by increasing or decreasing how much is filtered out through urine.

Hormones also help in this process. For example, antidiuretic hormone (ADH) signals the kidneys to hold on to water when your body needs it. Another hormone called aldosterone helps the kidneys retain salt and water, especially when blood pressure or blood volume is low.

The result of all this fine-tuned control is a steady internal environment, even when your fluid intake, weather, or physical activity changes. This balance is called homeostasis, and the kidneys are at the heart of it.

By managing both water and electrolytes, your kidneys help you stay hydrated, maintain stable blood pressure, and support normal body function every day.

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