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I'm here at Stanford Medical School with Neil Gesundheit,

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who is a faculty member here at the Med School.

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NG: Hi.

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SK: So, what are we going to talk about?

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NG: Well, the topic for today is Endocrinology, which is the study of hormones.

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NG: The word hormone is derived from the Greek word which means "arouse the activity."

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N: And what hormones do is they're chemical messengers that are made at one part of the body

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and typically go to another part of the body and, as suggested [by the name],

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"arouse the activity" and give function to another organ.

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S: So they essentially are a kind of signalling,

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a way to communicate between one part of the body and the other.

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N: Exactly. They are very sophisticated communicators,

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I think that's a perfect term.

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Another way to think of it is that our body can communicate directly--e.g., nerves innervate muscle,

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and when you want to contract your muscle you give a signal from your brain,

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it goes down the nerve and it directly attaches to the muscle and causes it to contract--

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Whereas hormones are more like the Wi-Fi of the human body:

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They are wireless. They are made in one place and go into the bloodstream--

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--which are like the airwaves, if you will--

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--and [the hormones] work on another part of the body at a distance,

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without directly, mechanically connecting to that part of the body.

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S: And hormones, are they a specific type of protein or a specific type of chemical,

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or are they pretty much anything that will do what you described?

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N: They are pretty much anything but they fall into two major categories:

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There are small molecules typically derived from amino acids,

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and those molecules are 300-500 daltons--aka, mmu--

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up to large proteins which can be hundreds and hundreds of amino acids in size.

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S: I see, so anything that has a signaling function...

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N: That's right, would be considered a hormone.

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N: And the other thing is, when we talk about hormones, is the three subcategories,

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we call some of them 'endocrine' hormones, where they get in the bloodstream and work at a far distance.

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And we'll give some examples with your diagram there in just a minute.

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But there are others that are called paracrine hormones,

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and paracrine hormones are more regionally active,

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So, they might be made, say, in one part of the body and work within a small distance of that site.

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N: And then the third category, which would be less common, is the autocrine hormones.

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And the autocrine are made directly in one cell and work on that same or the cell right next door,

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at a very small distance.

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S: I see. Are these things--I think I have a mental model for it--endocrine hormones

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are released, and faraway in the body they are picked up by some receptor,

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the paracrine hormones, is their effect small because they are only able to travel small distance?

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N: Typically the paracrine hormones do get into the bloodstream,

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but the concentration of the receptor--the receiving end, is right close by--

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so it tends to make the paracrine hormones work regionally, is the high concentration of

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the receptors is very close to the site of synthesis.

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S: I see.

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N: And the same with autocrine hormones, they are made and there is a very high concentration of

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the receiving end right at that cell.

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S: And, this might be a silly question, there are endocrinologists, are there paracrinologists?

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N: Well, that's a good point, I don't think so.

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I think we just--because the paracrine function of hormones was discovered later--

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we still carry this all under the umbrella of endocrinology.

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S: So all hormones are in endocrinology, the endocrine hormones are those working at far distances.

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N: That's right. I think that's a good way to summarize it.

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I like the diagram you have here because it illustrates some of the major endocrine ogans,

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the ones we'll be focusing on in later lectures. So the first one you showed very nicely,

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in the head, at the base of the brain, is that orange structure--and that would be

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the pituitary gland. The pituitary gland is called the "master gland" because

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from the pituitary gland we make hormones that work on yet other organs.

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So, I'll give you an example, one of the hormones made by the pituitary is called the

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thyroid-stimulating hormone, or the TSH.

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And after it leaves the pituitary, it goes into the circulation, and it acts on the thyroid where

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there are high receptors for TSH on the surface of the thyroid cells,

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and it stimulates the thyroid gland to make thyroid hormone, typically thyroxine (T4), or

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triiodothyronine (T3). Those are the two main circulating thyroid hormones.

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S: And what do those do?

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N: Those regulate metabolism, they regulate appetite, they regulate thermogenesis,

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they regulate muscle function--they have widespread activities on other parts of the body.

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S: They are kinda up-regulates or down-regulates the metabolism of your entire body

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N: That's right. So someone with hyperthyroidism will have very high metabolism,

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you may know the classic picture of someone with the high heart rate, rapid metabolism, weight loss--

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that would be someone with excessive amounts of thyroid hormone.

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And then you see pretty much the inverse picture when someone has a deficiency of thyroid hormone--

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hypothyroidism. So, it's critical to maintain just the right amount of all of these hormones, and

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thyroid hormones is a good example.

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But the ultimate regulation is from that pituitary gland.

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S: Right, this is kinda the master one, it sends a signal there and...

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N: That's right. And we'll talk later about feedback loops, because how does the pituitary know when

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to stop making TSH? Basically, like a thermostat, it can sense the level of thyroid hormone,

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and when those hormones are at just the right level, and not too high, it will decrease the amount of

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TSH it makes, if the levels are too low, it will stimulate production of TSH to make the

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thyroid gland make more thyroid hormone.

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S: Very cool. What else do we have here?

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N: The other hormones, some of the major ones, the pituitary, in addition to making TSH,

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it makes a hormone called ACTH, adrenocorticotrophic hormone, which acts on the adrenal cortex,

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and the adrenal is the gland that sits right on top of the kidney,

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and the outer layers of the adrenal gland are the adrenal cortex,

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and those are stimulated by ACTH.

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S: They are not related to the kidney, they just sit on top there?

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N: Right. They're related only in the sense that the blood supply is rich, like the kidneys' blood supply,

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and they happen to sit above the kidney. They are called 'ADrenal' because they are

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adjacent to the kidney, which is the 'renal' part,

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S: OH! That should've been obvious. X.x

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N: But they don't per se, filter blood or do any of the key functions of the kidneys.

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S: I see 8-) So what's their role?

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N: The adrenal glands make the adrenal hormones like cortisol, which regulates glucose metabolism,

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which maintains blood pressure and well-being,

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and then it makes mineralocorticoids like aldosterone which is important in regulating

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salt-water balance. You also have adrenal androgens, which are somewhat important.

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And those three hormones are the main hormones made by the adrenal cortex.

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S: I see 8-)

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N: The ACTH primarily regulates the cortisol and the adrenal androgens,

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and there's another system that regulates the mineralocorticoids, that we'll talk about later.

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S: Okay. And we have a few more organs here? :-9

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N: Also out of the pituitary we make luteinizing hormone and follicle-stimulating hormone.

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Those are abbreviated LH and FSH.

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And those act on the gonads, so in the male on the testis, and in the female on the ovaries,

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to stimulate development of sperm in the male, and oocytes (eggs) in the female,

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and also the production of gonadosteroids, predominantly testosterone in the male,

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and estradiol in the female.

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S: O.O...how many more...are we missing any thing?

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N: Well, there are two other hormones that are derived from the anterior pituitary,

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and those are the Growth Hormone (GH) which is critical for optimal growth (e.g., of long bones)

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S: Pituitary really does do a whole lot X.X

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N: It does! MUAHAHA!!

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S: hGH, human Growth Hormone?

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N: Right. and that works e.g., on long bones, and we would have prolactin (LTH),

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which in women is important in lactation, being able to breast feed after delivering a child.

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S: And insulin is...

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N: Insulin is key, but it doesn't come from the pituitary. So now we're gonna work our way down a bit,

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we talked about the thyroid gland making the thyroid hormones,

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and when you get to the pancreas, which is that yellow structure right in the middle,

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inside of the pancreas there are small islands called "the islets of Langerhans,"

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and the islets within the pancreas make endocrine hormones, like insulin and glucagon,

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But insulin is vital, without insulin you have diabetes. and without insulin you

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don't transport glucose into muscle, and remove glucose from the bloodstream normally.

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And the absence of insulin can produce all the symptoms of diabetes that we'll talk about later [?! :(

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S: And it seems, just structurally, you have the pancreas right here, you have the adrenal glands right

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there, they're all kinda near that interchange...because they're all so important...

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N: Yeah, that's a good observation. They all have a lot venous drainage from them,

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so when they make their hormones, it gets into the bloodstream rather quickly,

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because they are vital structures.

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S: Very cool 8-). I think we can leave it there, and for the next video you have some pictures which

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look pretty interesting =-D

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N: Okay, in the next video we'll talk about how you have to have the right amount of a hormone,

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or else things go awry.