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Endocrine System Intro


Okay, endocrine system, so we're gonna talk about the hormones that are released in our bodies. First, we'll talk about a few types of hormones. We're gonna get very specific, and this is a big, high-yield area. So, we have different types of hormones, we have steroid hormones, and the best thing about these guys is that they're non-polar, and what do we remember about non-polar substances?

They can cross the plasma membrane, so, popular MCAT question would be, steroid hormones, where do you expect them to bind to their receptors? And because they're non-polar and can cross the plasma membrane, they can get into and bind nuclear receptors inside the cell, versus peptide hormones. And we remember that peptides are polymers of amino acids, so they're large, and they're not necessarily nonpolar, unless we got extremely lucky.

So, they're not going to be able to bind to nuclear receptors, they're gonna bind to receptors on the cytoplasm. And a lot of these communicate through the second messenger systems that we discussed earlier, like cycolpain pathway and the IP3 dag pathway and so forth. Amino Acid Derived Hormones include epinfrin, no epinfrin, and these combined either inside or outside of the cell endocrine versus exocrine.

This is an important distinction, so we're gonna talk about the endocrine system, we'll talk about some exocrine stuff in GI. But exocrine stuff travels through ducts in the body, like through our GI tract and other ducts within the body, and they exert their influence close to where they are released. Versus endocrine hormones, which travel in the body through the blood, and go travel long distances to exert an influence off of ROA, and obviously, that's relative.

But the point here, is that endocrine hormones travel through the blood and can go throughout the body to exert their effect. The final definition is that of tropic hormones, which are hormones that stimulate a gland to produce other hormones. So, some hormones have a direct action in the body. Other hormones tell a gland to produce other hormones.

We'll talk about tropic hormones here. All right, this is kind of what I like to think of the centerpiece of this lesson, where we pick up some big MCAT points, by knowing this topic very well. So, we'll talk about the anterior, posterior, pituitary. First, we're gonna do the hormones of the anterior pituitary. You need to know them all, and know who releases them, and know what they do.

So, first hormone, FSH, follicle-stimulating hormone. Next hormone, luteinizing hormone. Next one, ACTH, adrenocorticotropic hormone. Next hormone, thyroid stimulating hormone. Next one is prolactin, and the last one is growth hormone, okay? Now, these are hormones of the anterior pituitary.

Hormones, next of the hypothalamus we're gonna talk about. These stimulate the anterior pituitary to release the hormones we've just discussed. So GNRH can release a hormone, which is released from the hypothalamus that caused the anterior pituitary to release FSH and LH. So obviously, this is a tropic hormone. Corticotropin releasing hormone stimulates interpituitary drugs ACTH, so that is also a tropic hormone.

CRH is because it's stimulating a gland to release another hormone. Next, we have thyroid hormone releasing hormone, also tropic, because it is stimulating interior pituitary. In fact, all of these are, cuz they are all stimulating interior pituitary prolactin to release a hormone. Prolactin luckily is not dopamine, and all of those other things that inhibit insulin and not tested.

And finally, growth hormone releasing hormone. And this thyroid hormone releasing hormone is often just referred to as Thyroid Releasing Hormone. Either definition, or to write it, either way is really fine. Okay, we need to know what each of these hormones of the anterior pituitary do. So, we're gonna discuss FSH and LH separate, so we'll hold off on those.

So now we're gonna talk about ACTH. ACTH comes down and stimulates the adrenal cortex to release a hormone called cortisol. Okay, and cortisol is a stress hormone that its action is to increase blood sugars, amongst other things, and remember, it's a stress hormone. So if you think stress, think cortisols being released.

We release a huge amount of cortisol when we wake up every morning. So, we can go from that nice, relaxed lying down position to deal with the stresses of being on our feet all day. Thyroid stimulating hormone, it acts on thyroid gland. And it causes the thyroid gland to release thyroid hormone. And there's an opportunity to talk about this later in but I'm gonna talk about it now.

Thyroid hormone, you should be familiar with what it does. So, you should think of it as kind of the thermogenic that increases metabolism. So, someone with increased thyroid hormone, they are going to be hot, they're going to have weight loss. They're going to have a lot of energy, they're going to have difficulty sleeping. Those are a few of the things that you should be aware of.

Some with high both iortaism is going to have weight gain. They're gonna be lethargic and. They're going to, or some of the other things we mentioned. So they'll be cold in general. And they'll have difficulty with mentation. They won't be thinking clearly.

Basically, things slow down with low thyroid hormone, and speed up with high thyroid hormone. Prolactin, you should know. So far, these are penthropic hormones, right? Because they act on a gland, in this gland here to cause release of another hormone. Prolactin is not tropic as a direct effect.

You should know that Prolactin causes breast development. And it causes milk production from the mammary glands, okay? And then growth hormone is also not tropic, because it has a direct effect, and it causes growth and development, muscle growth, bone growth, protein synthesis, things I think make sense to us. And another thing it does also, it increases blood sugar, so it makes sugar available in the blood for energy use.

You should also, with relation to growth hormone, be familiar with the terms gigantism and acromegaly. And as we all know, we grew, and grew, and then our growth plates closed, and then we stopped growing. Well, gigantism is an excess of growth hormone, while the growth plates were still open.

So, gigantism makes people be very tall. Acromegaly is an excess of growth hormone when the growth plates have already closed. And what this results in is instead of people being very tall, things grow longitudinally. So, very big boned people, and people who have later on set growth hormone, basically so they have acromegally growth hormone, after the growth plates have closed, their face changes, the bones develop and they kind of have a characteristic face.

So a great example here is the old WWF wrestler, Andre the Giant. Hopefully his memory never dies, so that this example is always pertinent. But he was both very tall, so he had some excess growth hormone. While his growth plates were still open, so before they closed. But he also had growth hormone excess after they closed. So, he had a classic acromegalic face with very large hands, and he was very big-boned throughout.

These people have very sweaty hands as well, so, you should be familiar with the differences between gigantism, acromegaly, specifically, how they relate to the growth plates.

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