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Intro to the Endocrine System : Basic overview of hormones and the endocrine system
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- I'm here at Stanford Medical School with Neil Gesundheit,
- who is a faculty member here at the Med School.
- NG: Hi.
- SK: So, what are we going to talk about?
- NG: Well, the topic for today is Endocrinology, which is the study of hormones.
- NG: The word hormone is derived from the Greek word which means "arouse the activity."
- N: And what hormones do is they're chemical messengers that are made at one part of the body
- and typically go to another part of the body and, as suggested [by the name],
- "arouse the activity" and give function to another organ.
- S: So they essentially are a kind of signalling,
- a way to communicate between one part of the body and the other.
- N: Exactly. They are very sophisticated communicators,
- I think that's a perfect term.
- Another way to think of it is that our body can communicate directly--e.g., nerves innervate muscle,
- and when you want to contract your muscle you give a signal from your brain,
- it goes down the nerve and it directly attaches to the muscle and causes it to contract--
- Whereas hormones are more like the Wi-Fi of the human body:
- They are wireless. They are made in one place and go into the bloodstream--
- --which are like the airwaves, if you will--
- --and [the hormones] work on another part of the body at a distance,
- without directly, mechanically connecting to that part of the body.
- S: And hormones, are they a specific type of protein or a specific type of chemical,
- or are they pretty much anything that will do what you described?
- N: They are pretty much anything but they fall into two major categories:
- There are small molecules typically derived from amino acids,
- and those molecules are 300-500 daltons--aka, mmu--
- up to large proteins which can be hundreds and hundreds of amino acids in size.
- S: I see, so anything that has a signaling function...
- N: That's right, would be considered a hormone.
- N: And the other thing is, when we talk about hormones, is the three subcategories,
- we call some of them 'endocrine' hormones, where they get in the bloodstream and work at a far distance.
- And we'll give some examples with your diagram there in just a minute.
- But there are others that are called paracrine hormones,
- and paracrine hormones are more regionally active,
- So, they might be made, say, in one part of the body and work within a small distance of that site.
- N: And then the third category, which would be less common, is the autocrine hormones.
- And the autocrine are made directly in one cell and work on that same or the cell right next door,
- at a very small distance.
- S: I see. Are these things--I think I have a mental model for it--endocrine hormones
- are released, and faraway in the body they are picked up by some receptor,
- the paracrine hormones, is their effect small because they are only able to travel small distance?
- N: Typically the paracrine hormones do get into the bloodstream,
- but the concentration of the receptor--the receiving end, is right close by--
- so it tends to make the paracrine hormones work regionally, is the high concentration of
- the receptors is very close to the site of synthesis.
- S: I see.
- N: And the same with autocrine hormones, they are made and there is a very high concentration of
- the receiving end right at that cell.
- S: And, this might be a silly question, there are endocrinologists, are there paracrinologists?
- N: Well, that's a good point, I don't think so.
- I think we just--because the paracrine function of hormones was discovered later--
- we still carry this all under the umbrella of endocrinology.
- S: So all hormones are in endocrinology, the endocrine hormones are those working at far distances.
- N: That's right. I think that's a good way to summarize it.
- I like the diagram you have here because it illustrates some of the major endocrine ogans,
- the ones we'll be focusing on in later lectures. So the first one you showed very nicely,
- in the head, at the base of the brain, is that orange structure--and that would be
- the pituitary gland. The pituitary gland is called the "master gland" because
- from the pituitary gland we make hormones that work on yet other organs.
- So, I'll give you an example, one of the hormones made by the pituitary is called the
- thyroid-stimulating hormone, or the TSH.
- And after it leaves the pituitary, it goes into the circulation, and it acts on the thyroid where
- there are high receptors for TSH on the surface of the thyroid cells,
- and it stimulates the thyroid gland to make thyroid hormone, typically thyroxine (T4), or
- triiodothyronine (T3). Those are the two main circulating thyroid hormones.
- S: And what do those do?
- N: Those regulate metabolism, they regulate appetite, they regulate thermogenesis,
- they regulate muscle function--they have widespread activities on other parts of the body.
- S: They are kinda up-regulates or down-regulates the metabolism of your entire body
- N: That's right. So someone with hyperthyroidism will have very high metabolism,
- you may know the classic picture of someone with the high heart rate, rapid metabolism, weight loss--
- that would be someone with excessive amounts of thyroid hormone.
- And then you see pretty much the inverse picture when someone has a deficiency of thyroid hormone--
- hypothyroidism. So, it's critical to maintain just the right amount of all of these hormones, and
- thyroid hormones is a good example.
- But the ultimate regulation is from that pituitary gland.
- S: Right, this is kinda the master one, it sends a signal there and...
- N: That's right. And we'll talk later about feedback loops, because how does the pituitary know when
- to stop making TSH? Basically, like a thermostat, it can sense the level of thyroid hormone,
- and when those hormones are at just the right level, and not too high, it will decrease the amount of
- TSH it makes, if the levels are too low, it will stimulate production of TSH to make the
- thyroid gland make more thyroid hormone.
- S: Very cool. What else do we have here?
- N: The other hormones, some of the major ones, the pituitary, in addition to making TSH,
- it makes a hormone called ACTH, adrenocorticotrophic hormone, which acts on the adrenal cortex,
- and the adrenal is the gland that sits right on top of the kidney,
- and the outer layers of the adrenal gland are the adrenal cortex,
- and those are stimulated by ACTH.
- S: They are not related to the kidney, they just sit on top there?
- N: Right. They're related only in the sense that the blood supply is rich, like the kidneys' blood supply,
- and they happen to sit above the kidney. They are called 'ADrenal' because they are
- adjacent to the kidney, which is the 'renal' part,
- S: OH! That should've been obvious. X.x
- N: But they don't per se, filter blood or do any of the key functions of the kidneys.
- S: I see 8-) So what's their role?
- N: The adrenal glands make the adrenal hormones like cortisol, which regulates glucose metabolism,
- which maintains blood pressure and well-being,
- and then it makes mineralocorticoids like aldosterone which is important in regulating
- salt-water balance. You also have adrenal androgens, which are somewhat important.
- And those three hormones are the main hormones made by the adrenal cortex.
- S: I see 8-)
- N: The ACTH primarily regulates the cortisol and the adrenal androgens,
- and there's another system that regulates the mineralocorticoids, that we'll talk about later.
- S: Okay. And we have a few more organs here? :-9
- N: Also out of the pituitary we make luteinizing hormone and follicle-stimulating hormone.
- Those are abbreviated LH and FSH.
- And those act on the gonads, so in the male on the testis, and in the female on the ovaries,
- to stimulate development of sperm in the male, and oocytes (eggs) in the female,
- and also the production of gonadosteroids, predominantly testosterone in the male,
- and estradiol in the female.
- S: O.O...how many more...are we missing any thing?
- N: Well, there are two other hormones that are derived from the anterior pituitary,
- and those are the Growth Hormone (GH) which is critical for optimal growth (e.g., of long bones)
- S: Pituitary really does do a whole lot X.X
- N: It does! MUAHAHA!!
- S: hGH, human Growth Hormone?
- N: Right. and that works e.g., on long bones, and we would have prolactin (LTH),
- which in women is important in lactation, being able to breast feed after delivering a child.
- S: And insulin is...
- N: Insulin is key, but it doesn't come from the pituitary. So now we're gonna work our way down a bit,
- we talked about the thyroid gland making the thyroid hormones,
- and when you get to the pancreas, which is that yellow structure right in the middle,
- inside of the pancreas there are small islands called "the islets of Langerhans,"
- and the islets within the pancreas make endocrine hormones, like insulin and glucagon,
- But insulin is vital, without insulin you have diabetes. and without insulin you
- don't transport glucose into muscle, and remove glucose from the bloodstream normally.
- And the absence of insulin can produce all the symptoms of diabetes that we'll talk about later [?! :(
- S: And it seems, just structurally, you have the pancreas right here, you have the adrenal glands right
- there, they're all kinda near that interchange...because they're all so important...
- N: Yeah, that's a good observation. They all have a lot venous drainage from them,
- so when they make their hormones, it gets into the bloodstream rather quickly,
- because they are vital structures.
- S: Very cool 8-). I think we can leave it there, and for the next video you have some pictures which
- look pretty interesting =-D
- N: Okay, in the next video we'll talk about how you have to have the right amount of a hormone,
- or else things go awry.
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