The Endocrine System – Biological Bases of Behavior (PSY, BIO)

00:01 Okay. So why don’t we start moving on to the endocrine system.

00:05 This is a really unique system that has wide ranging effects.

00:09 Now, what are some of the components of an endocrine system? But first off is that it’s a collection of ductless glands which release hormones directly into the circulatory system.

00:18 So it’s got this cascading effect, which is what sets it apart from some of the other systems that we’ve talked about so far.

00:25 So the effects are slow to initiate, but they’re prolonged in their response and they activate distant targets lasting a long period of time.

00:33 So as opposed to the quickness and the agility that was mentioned with our central nervous system and the peripheral nervous system and that we detect a sensory stimulus and we respond very quickly, the idea here is we don’t always need these superfast signals.

00:47 Sometimes we need something that’s low and slow and this is exactly the system that does that.

00:53 There are effects at several organs at the same time, there are things that can last for a long period of time, and the idea is the signals actually originated from the brain, but then they impact sort of the rest of your body.

01:06 So, that ability to communicate throughout is really, really useful and necessary.

01:12 So some of the endocrine glands that are important that you should know include, I’m just going to highlight some of them and we can’t go through all of them, but things like the pineal gland, the pituitary gland, the pancreas, the ovaries, testes, thyroid gland, we have the parathyroid gland, the hypothalamus, the GI tract, adrenal glands.

01:33 So you can see it’s pretty expansive and there’s a lot of components involved and they’re all related.

01:38 But we’re going to highlight on a few of these, okay? So the hypothalamus is the primary coordinator of the endocrine system and it activates the sort of the star of the show, which is the pituitary gland.

01:47 And the pituitary gland secretes hormones and neurotransmitters for growth, deals with reproduction and mental development.

01:54 So it’s causing the release of these transmitters that do a lot of really important things and it’s also known as the hypophysis.

02:01 Now, if you look at this diagram you can notice its location and notice its size.

02:06 It’s really, really small.

02:07 It’s not a big structure but it has really wide ranging effects.

02:13 The thyroid is another one that we want to talk about and this is located at the front of a neck and it regulates metabolism end energy use.

02:19 So you may have heard people mention before, “Oh, I’m slightly overweight because I have a thyroid problem.” That’s because as we just said right now it’s part of its function is to regulate metabolism and energy use, so if there are deficiencies or problems there, it can impact your ability to metabolize food and the amount of energy that you end up using.

02:40 The parathyroid is located behind the thyroid and it regulates calcium levels in blood and it impacts bone development.

02:47 So we should remember that parathyroid equals calcium in the blood and bone development, but that’s of importance a little bit later on.

02:55 Now, let’s take a deeper look at the adrenal glands and there are different components of it.

03:00 So the adrenal gland as a whole releases epinephrine and adrenaline which we’ve talked about pretty much almost in every lecture, which activates our fight or flight response and many other regulatory hormones such as cortisol which is important for during the fight or flight response, it’s important in terms of sleep, aldosterone, and other sex hormones.

03:18 The pancreas releases insulin and glucagon which is what allows us to modulate our levels of blood sugar and deficiencies in insulin where this can lead to things like diabetes, so extremely relevant.

03:31 And we have reproductive glands, which are testes and ovaries, and they release good old sex hormones, so also very, very important for things like the initiation of -- sorry, the expression of puberty and as part of modulating our sex drive.

03:47 So speaking of hormones let’s get into different class -- two different classes of hormones.

03:52 So the name is linked and based upon their felicity or their water-loving/water-hating relationship.

04:00 So the first class is hydrophilic, which is peptides and amino-acid derivatives, and we have hydrophobic, which is steroid hormones.

04:07 And if you want to try to remember which is what, you know people have phobias, meaning they’re afraid of things.

04:12 Well, hydrophobic means afraid of water, loosely put, so it means the opposite of wanting to be around water, whereas hydrophilic is water-loving.

04:21 So we’re referring to sort of their water solubility, and the hydrophilic ones are little more water soluble versus the hydrophobic, which are not.

04:28 They’re water-hating or water-afraid.

04:30 So peptide hormones, they bind to receptors on cell surface and they’re stored in vesicles until they’re needed, a lot like the transmitters, and their action is more rapid and short-lived.

04:39 For an example, insulin, they communicate with the interior of the target of the cell by way of secondary messenger. So it’s a cascade effect.

04:47 So as opposed to a transmitter binding to a receptor site, that would be very fast, that’s called ligand-gated, and ligand refers to the transmitter, and secondary messengers or things using G-coupled proteins are a little bit slower and here’s an example of that.

05:06 It’s composed of small to large amino acid chains and these are collectively referred to as polypeptide.

05:12 So the poly refers to more than one, and peptide is referring to the fact that we’re talking about amino acids here.

05:18 Steroid hormones are synthesized from cholesterol only when they’re needed and can pass pass through a membrane.

05:25 And part of the reason why they’re able to pass through membrane is again looking at their lipid solubility.

05:30 So the more lipid soluble something is the easier it is for it to move through membranes because membranes are primarily composed of phospholipids.

05:39 Steroid hormones bind to the cytoplasmic receptor and they enter the nucleus and then go on to alter gene expression by regulating DNA transcription.

05:46 So that’s a lot of stuff that we just threw out there and were involving some biology and genetics, but what we’re saying simply is that steroid hormones have this ability to have long-lasting effects in terms of gene expression and regulating DNA transcription which can then go on to actually impact protein expression.

06:08 So the idea is that these hormones can have these dramatic long-lasting changes and effects.

06:14 So the effects are slower to initiate but are longer-lasting.

06:17 So that’s a key point to remember when we’re talking about hormones and when we’re talking about the endocrine system as a whole.

06:25 Tyrosine derivatives include two classes of hormones including the thyroid hormone and also catecholamines.

06:32 So the thyroid hormone is produced in the thyroid, thus, the name, and increases overall metabolic rate and body temperature.

06:39 And in children, it actually stimulates growth and the two that you want to be aware of are T3 and T4.

06:45 Catecholamines include a lot of things we’ve already talked about, the transmitters including epinephrine and norepinephrine, adrenaline and noradrenaline is another name for them.

06:55 So let’s take a look at the autocrine versus paracrine versus the endocrine systems and this something that might also come up in your MCAT because they’re going to want you to understand and appreciate the differences and a good to remember is the names.

07:10 So the endocrine you should know because we talked about it and we said that it’s low and slow.

07:14 The autocrine system and the autocrine signaling is a form of self-signaling in which the cell secretes a hormone or chemical messenger called an autocrine agent that binds to an autocrine receptor that is on the same cell.

07:27 So it leads to changes in that specific cell.

07:29 So almost like an autoreceptor.

07:32 So it’s causing impact upon itself.

07:34 So it’s sort of proximity of effect is pretty small, it’s just a cell that it’s communicating with.

07:39 Then you have the paracrine signaling which is a form of cell-to-cell communication in which a cell produces a signal to induce changes in nearby cells altering the behavior of or differentiation of those cells.

07:51 So it’s cell-to-cell communication.

07:53 And endocrine is that broader, longer-lasting, more diffuse activation.

08:00 So how do we control or stop or modulate secretion of these different things? Well, it goes through a process, using the HPA axis is a great example of looking at all the different components of the endocrine system and how they actually feedback upon themselves and this a primary example of a process called negative feedback.

08:21 And we’ve mentioned this in a couple of the other modules so this might be repeat, but I think it’s really important that we still look at it again.

08:29 This is collectively known as the HPA axis.

08:32 So we start with the hypothalamus.

08:33 The hypothalamus releases something called CRH or corticotropin-releasing hormone, and then it goes on to activate the anterior pituitary gland, which goes on to release adrenocorticotropic hormone or ACTH, and that goes on to activate the adrenal cortex, and the adrenal cortex releases cortisol.

08:53 And cortisol levels are detected and what happens is when we achieve the appropriate level of cortisol, there are receptors that detect that and send the signal back to the hypothalamus saying “You know what, I don’t think we need any more CRH because we have enough cortisol,” and it sends a similar signal to anterior pituitary to say, “We got enough ACTH because we don’t need any more ACTH because we have enough cortisol.” So we call that overall process of aligned going positive, release, release, release, and then sending a signal back saying, “I think we’re good we have enough,” as negative feedback because we’re causing release positive, causing release that’s positive, causing release that’s positive, and then we’re needing to turn that off and that’s the negative off signal or the negative feedback.

09:40 Okay. Let’s take a look at the endocrine system on behavior.

09:43 We know that both the nervous system which is quite fast and the endocrine system which is low and slow respond to both internal and external stimulus.

09:51 So it’s not that the nervous system is the only way we see a response, the endocrine system is involved and it’s like I said usually longer-lasting and long-term responses.

10:00 So the short-term and long-term response can stimulate both direct effects, so we need the fast stuff which is the nervous system, the slow stuff which is the endocrine system, collectively together will impact behavior, the behavioral response and can also impact behavioral modification.

10:19 Now, the release of adrenaline is an important point as well, and that’s done by the adrenal medulla which is activated by the hypothalamus.

10:27 And we know that processes like behavioral modification or CBT, cognitive behavioral therapy, employ changes in this process in order to modify our behavior.

10:38 So that’s a really, really cool thing.

10:39 So you’re actually using your ability to cognitively shift changes in activation in order to impact your behavior.

10:49 So here we’re seeing a link between physiology, psychology, and behavior pretty much the scope of this course.