How do kidneys control blood pressure?

Your kidneys play a major role in controlling your blood pressure. While the heart pumps the blood, the kidneys help manage how much fluid is in your system and how tight or relaxed your blood vessels are. These two factors—fluid volume and vessel tone—have a direct impact on blood pressure.

One way the kidneys help is by regulating the amount of fluid in your blood. When you drink water, the kidneys decide how much to keep and how much to remove. If they hold on to more water, your blood volume increases, and this raises blood pressure. If they remove more water through urine, blood volume drops, and pressure goes down.

The kidneys also release a hormone called renin, which kicks off a chain reaction known as the renin-angiotensin-aldosterone system (RAAS). This system helps the body respond to changes in blood pressure. Renin signals the body to narrow the blood vessels and hold on to salt and water. Both actions raise blood pressure when it drops too low.

Salt plays an important part in this process. When your salt levels rise, your body holds on to more water, which increases blood pressure. The kidneys help manage this by adjusting how much salt they excrete.

So, while it may seem like the heart is the main player in blood pressure, the kidneys are quietly working in the background to keep everything in balance. When they do not work properly, blood pressure can become too high or too low—often without warning.

Understanding how the kidneys influence blood pressure helps explain why kidney health and heart health are closely connected. Keeping your kidneys healthy is one of the best ways to support a stable blood pressure over time.

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