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Endocrine System

Teacher/Instructor Patrick Roisen
Patrick Roisen

M.Ed., Stanford University
Winner of multiple teaching awards

Patrick has been teaching AP Biology for 14 years and is the winner of multiple teaching awards.

The endocrine system signals information to help the body function. Each gland in the endocrine system produces a different type of hormone to regulate all the different types of functions in the body. The endocrine system is different from the nervous system because messages travel much more slowly but responses last much longer.

When I tell students that we're going to be working on the endocrine system they look at me like "aah what?" When I tell them that we're going to be studying hormones they go ooh they know what that is. The endocrine system is the proper name for the hormone system and the endocrine system along with the nervous system controls and coordinates the activities of the body and helps maintain homeostasis. Now the endocrine system tends to focus more on all body longer term regulation regulating things such as growth, functioning of the immune system things like that as opposed to the nervous system which is more specific like move this arm, your hormone system doesn't do that.

Now the basic mechanism of how the endocrine system works is that a gland or sometimes individual cells will release a chemical signal called a hormone into the blood stream and when the heartbeat mmh mmh it sends the blood crossing throughout the body so that hormone may go anywhere in the body but ultimately it will bind to a special protein within or on the surface of the target cell and that protein has the right shape to receive that hormone. Then that target cell will carry out whatever response it's supposed to do in response to that particular hormone so one hormone can have differing effects based on what cell it's hitting for example testosterone can cause muscles to grow or hair to fall out but testosterone can cause hair to grow here or it can cause hair to grow far another places.

Now there are several types of hormones. The two basic categories you can put them in to all the ones that are lipids i.e. they're non polar molecules versus the ones that are not po- that are polar molecules so lipids in the most common of this is are the steroid hormones are the ones because they non polar they can pass easily through the cell membrane through the plasma membrane of the cell and get into the actual cell whereas the other ones have to stay on outside. Somewhere within the cell where they're floating around the cytosol or within the actual nucleus they'll bind to a receptor protein then they will activate a gene or in some cases they'll turn off or inhibit a gene and thus causing the response.

The peptides which are chains of the amino acids or the amines which are individual amino acids that have been modified, these typically bind to a receptor on the upper surface of the plasma membrane and when they do that, that protein will cause changes to occur activating other chemicals within the cell that will then carry out that activity. These other chemicals that are created are called second messengers, if the hormone itself is the first messenger they newly created or activated as molecules inside the cell would be the second messenger. One of the most common second messengers is something called Cyclic AMP often written as little c AMP it's created by an enzyme called adenylyl cyclase I'm just tossing that up because if you see that that's cyclic AMP that's the second messenger that's not a steroid hormone. You are very familiar with many of the steroid hormones if you ever see ster in the name of something it's probably a steroid hormone things like testosterone, estrogen, aldosterone which you probably never heard of but it's a steroid hormone. Well these guys couldn't include things such as insulin for example.

Now if we take a look at this diagram over here there are a number of specialized organs in the body that are dedicated towards releasing hormones and we would call these glands but there's a bunch of other organs that do release hormones even though they're not specialized for, your stomach for example can release some hormones. Now the I could go through every gland and through every hormone that they release but that would make this go from a 5 minute video to a 20 minute lecture so I'm just going to focusing in on one that's the pituitary gland. The reason that I'm mentioning the pituitary gland is because the anterior bumper lobe of the pituitary gland is deemed sometimes called master gland of the body because it releases a bunch of tropic hormones that control or regulate the behavior of many of the other glands the for example release a number of gonadotropin or gonado tropic hormones. If you think about that gonad and trop controls gonads! Those are the ones that are regulating the actions of the gonads either the ovaries if you're a girl or testis if you're a guy. They will release a number of different hormones and the pituitary gland releases a ton of them if you see h at the end of one of these that stands for hormone and if you see s that stands for stimulating so if you see for example fsh that's stands for follicle stimulating hormone that stimulates the follicles that are down on the ovaries and helps trigger off the menstrual cycle while tsh for example, as is the thyroid stimulating hormone that triggers the thyroid to start producing it's chemicals so if you want to learn more about this just open up your textbook and go to the page where it has the diagram that explains what each of these hormones do and it's not that hard once you start learning it.