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Adrenal Cortex: Aldosterone and Body Fluid Balance

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  • 0:38 Mineralocorticoids
  • 1:44 Aldosterone
  • 2:29 Renin-Angiotensin System
  • 4:17 Lesson Summary
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Lesson Transcript
Instructor: Rebecca Gillaspy

Dr. Gillaspy has taught health science at University of Phoenix and Ashford University and has a degree from Palmer College of Chiropractic.

Mineralocorticoids are a type of steroid hormone secreted by the adrenal cortex. In this lesson, you will learn about the main mineralocorticoid, aldosterone, and how it regulates your body's salt and water balance.

Adrenal Cortex

The three types of steroid hormones secreted by the adrenal cortex
Adrenal Cortex

On top of your kidneys sit endocrine glands called the adrenal glands. Each gland contains an outer cortex that is referred to as the adrenal cortex. From this cortex, we see the secretion of three different types of steroid hormones: mineralocorticoids, glucocorticoids and sex hormones. In this lesson, we will learn about the main mineralocorticoid called aldosterone and the important role it plays in balancing salt and fluid levels within your body.

Mineralocorticoids

Mineralocorticoids are hormones that help regulate the salt and water balance in the body. The two important salt ions that are involved in this regulation are sodium and potassium. As we often see in biochemistry, where sodium goes, water follows.

When we look at the body, we see that mineralocorticoids target the kidneys and tell them to reabsorb, or hold onto, sodium so it does not leave the body in urine. Because water follows sodium, the body effortlessly reabsorbs water along with the sodium.

Water balance is closely regulated by your body, and it's important that your body keeps a close eye on the amount of fluid it carries around. One reason is because this influences your blood volume and your blood pressure.

We know that the cardiovascular system is a closed system. Therefore, if you have more fluid in your blood, you essentially have more blood in your cardiovascular system. This added volume increases the pressure within your blood vessels, which is measured as your blood pressure.

Aldosterone

The renin-angiotensin system is activated when the kidneys detect low blood pressure.
Renin-Angiotensin System

Aldosterone is the main mineralocorticoid secreted by the adrenal cortex. Your adrenal cortex will release aldosterone when your blood pressure gets too low.

Why does this happen? Well, as we just learned, mineralocorticoids such as aldosterone make your kidneys reabsorb sodium, which causes water to follow. This in turn increases blood volume and blood pressure back to normal. This is yet another example of how your body takes care of you without your conscious awareness. Even when you're tucked away sound asleep in bed at night, this process and many others are at work. It really makes you think about how amazing and smart your body is.

Renin-Angiotensin System

For example, if we take a closer look at the regulation of your blood pressure, we see that your kidneys are able to detect when your blood pressure is low. This triggers the release of a substance that we previously learned about called renin and the start of the renin-angiotensin system. Renin is produced by specialized cells within the kidneys in response to a drop in blood pressure. This initiates the hormonal cascade that leads to the production of angiotensin II. Angiotensin II is a powerful stimulator of aldosterone release. Once the aldosterone is released, blood volume and blood pressure rise.

One additional thing that you may have taken notice to is that your blood normally holds on to a fair amount of sodium. Sodium is used by your body not only in blood pressure regulation but in other functions, such as muscular contractions.

If your blood sodium level drops, this triggers aldosterone release from the adrenal cortex, which causes sodium to be reabsorbed, bringing the level back up to normal. Of course, as we see with many things in health, you can have too much of a good thing. If your body retains too much sodium and water, this can lead to unhealthy conditions, like high blood pressure.

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