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In this lesson, we’ll go over the main differences between ADH and aldosterone, including where they originate in the body, their functions, and their mechanisms.

Definitions of ADH and Aldosterone

Picture a hot summer day. Your heart is pounding as you finish your afternoon run. Your mouth is dry and your skin is soaked with sweat. The bright sun beats down on your shoulders, and you’re desperate for a nice cool drink.

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What really causes you to feel thirst? How does your body know it’s time for an icy lemonade?The answer comes down to the chemicals in your body called hormones. Hormones are secreted by glands and organs, and they tell your body what to do or how to feel. When you’ve lost too much water, hormones play an important part in communicating your thirst to the rest of the body.

Two hormones have very specific jobs of controlling the kidneys, the bean-shaped organs in the back of your abdomen responsible for managing water balance. Antidiuretic hormone (or ADH) and aldosterone tell the kidneys to hold onto water if you become too dehydrated. Before we explore the differences between these two hormones, let’s look at some basic kidney anatomy.

Kidney Anatomy and Function

Your kidneys are important organs for maintaining the right amount of water in your body. When there’s too much water, it’s released as urine. If you don’t have enough water, your kidneys help hold onto it, so you urinate less.

The kidneys function in these ways through little compartments made of tiny tubules called nephrons. The tubules are responsible for reabsorbing water and salt when the body needs it, and carrying anything the body doesn’t need to the bladder as urine. The liquid inside the tubules is called filtrate, and that’s what will become urine. The liquid outside the tubules is called the interstitial fluid and will eventually go back into the blood. The tubules wind through the nephron, collecting water and salt.

ADH and aldosterone work mainly in the last part of the tubule, the collecting duct.

ADH vs. Aldosterone

Now that we know where these hormones work in the kidney, let’s hone in on the differences between the two: where they’re made, their structures, and their mechanisms.

Where They Are Made

ADH is a hormone made in the hypothalamus, the part of the brain responsible for a wide variety of the body’s metabolic processes. ADH is moved to the posterior pituitary gland just beneath the hypothalamus, where it is secreted into the blood.

Aldosterone, on the other hand, is made right on top of the kidney in a tissue called the adrenal gland. The adrenal gland also releases aldosterone into the blood, much like the posterior pituitary releases ADH. Now let’s take a closer look at the structure of both ADH and of aldosterone.

Structure

ADH is a peptide made up of nine amino acids: tyrosine, phenylalanine, glutamine, asparagine, proline, arginine, glycine, and two instances of cysteine. Aldosterone, on the other hand, is a mineralocorticoid, which is a corticosteroid made of cholesterol. Mineralocorticoid is similar in structure to sex hormones like estrogen, and it’s much smaller than ADH.

Mechanisms

As we discussed, both hormones work in the collecting duct of the kidney. But how, precisely, do they function within the collecting ducts? Let’s explore. First, we’ll take a closer look at the mechanisms ADH possesses, followed by a closer look at those possessed by aldosterone.

ADH tells the kidney cells to transport more proteins called aquaporins, which let water back into the blood. The aquaporins are already made inside the cell, and the ADH just tells the cell to move them to the surface of the tubule for transport into the blood. These proteins are essentially holes that let water escape its fate as urine and go back to the blood, thereby keeping the body more hydrated. You can remember this by remembering that aqua means water and porin refers to holes.Aldosterone also helps to prevent dehydration, but it does so by prompting the blood to take up more salt. This might sound counterintuitive since salt makes you thirsty, but that’s actually just the point. Water likes to follow salt to make sure your body stays in balance.

If there is more salt on one side of the cell, water follows. So, when cells in the collecting duct push salt out into the blood, water leaves the filtrate to follow the salt. The result is more water in the blood. Think of water like a puppy and salt like the owner – wherever the salt goes, the water is sure to follow.Unlike ADH, which causes pre-made proteins to go to the surface, aldosterone prompts the creation of new proteins that move the salt. The aldosterone enters the nucleus, or brain of the cell, and tells it to make proteins that help move salt back into the blood.

Think of ADH like a prefab clothing store where pre-made outfits are ready to go, and think of aldosterone like a tailor who only makes custom suits.

Lesson Summary

Let’s review all that we’ve learned. In summary, the kidney is an organ that filters your blood, keeping water in balance in your body. Nephrons are the working units of the kidney and are made of tubules designed to reabsorb salt and water. Antidiuretic hormone (ADH) and aldosterone are hormones that tell your kidney to put water back in the blood. ADH is a hormone made in the hypothalamus, the part of the brain responsible for a wide variety of the body’s metabolic processes, while aldosterone is made right on top of the kidney in a tissue called the adrenal gland.

Also remember that hormones are chemical messengers secreted by various organs and glands that communicate with different parts of the body. Both work in the collecting duct – ADH causes it to take up water, whereas aldosterone causes it to take up salt and, in turn, causes water to follow. ADH is a peptide hormone made in the brain, and aldosterone is a corticosteroid made in the adrenal glands.

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