Biological basis of behavior: Nervous system
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Endocrine system and influence on behavior - Part 1
Voiceover: I want you to imagine with me that you're a cell in the brain. Let's say you're a member of the hypothalamus right here. As a part of the hypothalamus one of your jobs is to regulate how much fluid is in the blood volume at any given time. You just got informed by another part of the brain that your body cell down in the kidneys right here has been making urine like a madman all day, and now the fluid volume in the blood is a little bit low. You want to tell him to stop but how do you go about doing that? I mean one way the body communicates is through the nervous system and sending messages down the hardwired, prelaid tracks of the nervous system through nerves but there isn't really an established connection between you and him. What you decide to do is you decide to put a message in a bottle of sorts and float it down the bloodstream to him and hope that it gets there. You send that message his way and he receives it. He opens that message and he sees that you want him to close the permeability to water and he does that and fluid volume begins to be restored again. That process of sending a message from one part of the body to another part of the body through the bloodstream forms the basis of the endocrine system. The endocrine system. The endocrine system is a system of glands that produce chemical messages called hormones that travel from one part of the body to another part of the body through the blood in order to elicit an effect. In order to make a change in what's going on in a different part of the body. In the effects that are caused by the endocrine system cooperate with the nervous system in order to control the body's internal environment and homeostasis. The endocrine system and the nervous system are really related. They're almost like cousins. They're really similar but they're kind of unique. The nervous system is kind of like the hare in the children's story with the tortoise and the hare and the endocrine system would be the tortoise. The nervous system is really, really fast and you see results in milliseconds. The endocrine system in comparison is fairly slow and it might take minutes to even days or weeks to see the effects of these hormones. Like the children's story with the tortoise and with the hare, the tortoise as fast as he go he runs out of steam pretty quickly and the endocrine system as it goes a little bit slower but it will last longer. The effects while slower had a more lasting effect in the body with the endocrine system. Anyway, the chemical messages called hormones that the endocrine system utilizes they can be broken down into three distinct classes. First you have proteins and polypeptides. Proteins and polypeptide hormones like any other proteins in the body are made up of amino acids and they can be really small. As small as three or so amino acids which is pretty tiny when you think about it because an amino acid is a fairly small collection of atoms and if you're talking about three amino acids that's only a few atoms all the way up to hundreds and hundreds of amino acids in a polypeptide chain. Typically after you get about a hundred amino acids in a chain you start calling it a protein and that holds true for hormones as well. The second class after proteins and polypeptides are steroid hormones. Unlike proteins and polypeptides that are made up of amino acids steroid hormones are typically derived from cholesterol which is a lipid. From cholesterol. Steroids are made up of lipids and have lipid-like qualities like they're not charge and they can pass through cell membranes. That might mean the receptor instead of being on the outside of the cell it's on the inside of the cell. You've got proteins and you've got steroids and then you've got a class called tyrosine derivatives. Tyrosine is an amino acid and this class of hormones, the reasons it's separate is that they're derived from tyrosine. Tyrosine can be manipulated in order to make a couple different hormones. The two main classes of tyrosine derivatives are thyroid hormones and catecholamines. Catecholamines, I hope I spelled that right. Catecholamines. Catecholamines are the hormones that are made in the adrenal medulla and they include epinephrine and nor epinephrine. A little bit more common name outside of the medical community for epinephrine is adrenaline. Adrenaline is a little bit more familiar because we hear it when you're really excited and your fight or flight response. These are the three main classes of hormones and we see that they're classified by structure but they're also classified by function in a separate system. Even though all these hormones are functioning in the endocrine system not all of them have endocrine function. There's a class of hormones that are considered to have autocrine function and these are hormones that elicit a response at the cell that they're made or the cell immediately next to the cell that makes the hormone. In addition to autocrine signalling there's paracrine signals. This is more the regional effect. One example of paracrine signals are between the hypothalamus and the pituitary gland which I'll show you in a second. Those are really close. Yeah, there's not a hard line that gets drawn with where paracrine signal function ends but generally these are regionally acting signals. Then the last class are the endocrine signals. Those are the classic hormones that are set to function at a distance in the body and their response is elicited somewhere far away. Let's say the pituitary gland traveling all the way down to the gonads. That's a pretty long distance in terms of hormone size and blood vessel length. Those are called endocrine glands. Now that we've covered how hormones are classified I want to talk about the main organs of the endocrine system that use these hormones to communicate. I went ahead and pre wrote out to save a little bit of time. The first organ that I want to talk about in the endocrine system is the hypothalamus. The hypothalamus is a member of the endocrine system but it's also a member of the nervous system. It's right here in the brain. It's about the size of a grape. As a member of the nervous system it's taking in the signals that are being stimulated by the sensory nerves. It takes those signals and it kind of funnels them into the endocrine system through the pituitary gland by controlling the pituitary gland. The pituitary gland is often known as the master gland. It's situated right here below the hypothalamus and if the hypothalamus is about the size of a grape in the body, the pituitary gland is about the size of a green pea and it's tiny but it's role is huge in that it is principally involved in stimulating the other endocrine glands which are ultimately gonna cause any of the effects that are happening in the body. The first organ that it stimulates going down the list here is the thyroid gland. It stimulates the thyroid gland through thyroid stimulating hormone. The thyroid gland is a gland that wraps around the trachea which is your windpipe and you can feel it when you swallow, but the thyroid gland's main role is regulating our body's metabolism. Up regulating or down regulating the entire body and it does that through the thyroid hormones T3 and T4. Another name for T3 is triiodothyronine and another name for T4 is thyroxine, but those are the thyroid hormones that are a member of the thyrosine derivatives that I was talking about a little bit earlier. Behind the thyroid gland are four spots that are kind of collectively known as the parathyroid gland. I'm drawing them on the front but I want to be clear that these spots are on the back of the thyroid gland and the parathyroid gland is principally or chiefly involved in regulating our body's calcium levels. It does that through its hormone parathyroid hormone. Moving down the list we have the adrenal glands right here on top of the kidneys. They're called adrenal glands because they're adjacent to the kidneys and another name for the kidneys are the, the whole kidney system is the renal system. The adrenal glands are stimulated by the pituitary's release of adrenocorticotropic hormone and then they ultimately release their hormones. There are two separate areas of the adrenal glands. You've got the cortex of the adrenal glands which is the outside and the medulla which is the inside of the adrenal glands. The cortex is where the adrenal steroid hormones come from and so you got your glucocorticosteroids and your mineralocorticosteroids and those are things like cortisol and aldosterone. Those have a lot of functions in the body as far as regulating fluid volume and the stress response and in the medulla that's where the catecholamine hormones are made. Again, those catecholamines were the second class of thyrosine derivatives that I mentioned earlier. Moving down the list even further we have the gonads. In females those are your ovaries. In males your testes. The gonads are stimulated by the pituitary's release of FSH and LH which is follicle stimulating hormone and luteinizing hormone. The gonads then take that stimulation and release their hormones, the sex hormones. In ladies that's mostly progesterone and estrogen and in males testosterone. Those are your gonads. Outside of that pituitary signalling system is the pancreas right here. The pancreas isn't stimulated by the pituitary gland directly but it does release some pretty important hormones insulin and glucagon which function to regulate the blood sugar level. Again, the blood sugar level is pretty tied into the metabolism as glucose is kind of the backbone molecule that we get all of our energy from.