Alright. In this video, we are going to talk about ADH, or antidiuretic hormone, as well as aldosterone, and then I will take you through the steps in the renin-angiotensin-aldosterone system, or the RAAS system. Let's first talk about ADH. ADH helps to control blood pressure and blood volume in the body by regulating the reabsorption or excretion of water in the kidneys. So if we have more ADH, that's going to cause more reabsorption of water. If we have lower levels of ADH, that's going to cause more excretion of water. ADH is secreted from the posterior pituitary gland, in response to three things.
One is low blood volume. So if we have hypovolemia, which is not enough blood volume, then more ADH will be produced. That will cause more reabsorption of water, which will help to bring up that blood volume. Also, the second thing is if the body senses that blood pressure is low, it will want to bring that up. And the way it does that is it releases ADH, which causes more reabsorption of water at the kidneys, which helps to increase the blood volume, which will increase blood pressure. And then the third thing the body does if it senses hypernatremia. So if we have concentrated blood, so it's concentrated with sodium, we want to try to dilute it. And in order to do that, we release ADH, causes reabsorption of water, and that will help dilute the blood and bring those sodium levels back down to normal. So those are the three things that cause the body to release more ADH from the posterior pituitary gland. And ADH is going to be an important hormone to remember. And we will be talking about different conditions and disorders that cause issues with ADH.
Okay. Now, let's move to aldosterone. Aldosterone is a hormone that increases blood volume and blood pressure by causing kidney reabsorption of both water and sodium. So unlike with ADH, we were just reabsorbing more water, with aldosterone it's both sodium and water. In addition, aldosterone will cause excretion of potassium. So the release of aldosterone is controlled by the renin-angiotensin-aldosterone system, which I will go through those steps now.
So if you're following on the cards, the steps I'm going to go over are on card 9. So the whole system basically kicks off when there is decreased blood flow to the kidneys, which usually means that there is low blood pressure in the body. So when there's this decreased blood flow to the kidneys, the kidneys release renin. Renin in turn activates angiotensinogen into angiotensin I. Angiotensin I is converted in angiotensin II by ACE, which is angiotensin converting enzyme. And that is produced by the lungs. Then angiotensin II causes a number of actions to take place, all of which increase blood pressure in the body. The first thing that angiotensin II does is that is causes vasoconstriction of the afferent arterioles in the nephrons, in the kidneys, which increases sodium and water reabsorption, okay?
The second thing that angiotensin II does is that it causes aldosterone to be released from the adrenal cortex, which, as we talked about, causes the reabsorption of sodium and water at the kidneys, which helps to increase blood pressure and blood volume. Then it also causes vasoconstriction of blood vessels throughout the body. So by constricting those blood vessels, that also helps to bring up that blood pressure. So again, all three of these things that angiotensin II does are all intended to help increase that blood pressure when there is low blood pressure initially.
Alright. In my next video, I will be going over even more endocrine hormones that are important to know. If you find these videos helpful, be sure to like our video here, and leave us a comment and let us know what you think. So take care, and I'll see you in the next video for more hormones!
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