Placeholder Image

字幕表 動画を再生する

  • SALMAN KHAN: I'm here at Stanford Medical School

  • with Neil Gesundheit, who's a faculty member here

  • at the med school.

  • NEIL GESUNDHEIT: Hi, Sal.

  • SALMAN KHAN: So, what are we going to talk about?

  • NEIL GESUNDHEIT: Well, the topic for today

  • is endocrinology, which is the study of hormones.

  • And the word hormone is derived from the Greek word

  • which means arouse the activity.

  • 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 to, as suggested,

  • arouse the activity and give function to another organ.

  • SALMAN KHAN: So they're essentially

  • kind of signaling, a way to communicate

  • between one part of the body and the other.

  • NEIL GESUNDHEIT: Exactly.

  • They're very sophisticated communicators.

  • I think that's a perfect term.

  • And I think the other way to think of it

  • is our body communicates in some ways directly.

  • For instance, 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're wireless.

  • They are made at one place.

  • They go into the bloodstream, which is like the airwaves,

  • if you will.

  • And then they work on another part of the body at a distance,

  • without directly connecting to that part of the body

  • mechanically.

  • SALMAN KHAN: And hormones, are they a specific type of protein

  • or a specific type of chemical?

  • Or are they really anything that does what you just described?

  • NEIL GESUNDHEIT: It's pretty much anything,

  • but they fall into two major categories.

  • There are small molecules that typically

  • derive from amino acids.

  • And those molecules are just 300 to 500,

  • at most, daltons, which are molecular mass units, up

  • to large proteins that can be hundreds

  • and hundreds of amino acids in size.

  • SALMAN KHAN: I see.

  • So anything, anything that really has this signaling

  • function.

  • NEIL GESUNDHEIT: That's right, would be considered a hormone.

  • And the other thing is we talk about hormones

  • in three sort of subcategories.

  • We call some of them endocrine hormones,

  • where they really get into the bloodstream

  • and work at a far distance.

  • And we'll give some examples with your diagram

  • right 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, let's say, in one part of the body

  • and work within a small distance of that site of synthesis.

  • And then the third category, which is less common,

  • would be autocrine hormones.

  • And the autocrine hormones are actually

  • made directly at one cell and work on that same cell

  • or in this cell right next door, at a very, very small distance.

  • SALMAN KHAN: I see.

  • So, the endocrine hormones, I think

  • I have a mental model for it.

  • They're kind of released far away in the body someplace.

  • If they're picked up by the right receptor,

  • they'll have the right function.

  • The paracrine hormones, is their effect small

  • because they only are able to travel a small distance?

  • Or is it something else?

  • NEIL GESUNDHEIT: Typically the paracrine hormones

  • do get into the bloodstream, but the concentration

  • of the receptor, the receiving end, as you suggested,

  • is right close by.

  • So what tends to make a paracrine hormone

  • work regionally is that the high concentration of the receptors

  • are very close to the site of synthesis.

  • And the same with autocrine, is often they're made,

  • and there's a very high concentration of the receiving

  • end right at that cell, right next to that cell.

  • SALMAN KHAN: And this might be a silly question,

  • but it's called endocrinology.

  • Are there paracrinologists?

  • NEIL GESUNDHEIT: Well, it's a good point.

  • I don't think so.

  • I think we just, perhaps because the paracrine function

  • of hormones was discovered later,

  • we still carry this all under the umbrella of endocrinology.

  • SALMAN KHAN: Right.

  • So all of hormones is endocrinology,

  • even though endocrine hormones are

  • the ones that act at far distances.

  • NEIL GESUNDHEIT: That's right.

  • I think that's a good way to summarize it.

  • Now I like the diagram that you created here

  • because it illustrates some of the major endocrine organs,

  • the ones we'll be focusing on in later lectures.

  • So the first one that you showed very nicely in the head,

  • at the base of the brain, is that orange structure.

  • And that would be the pituitary gland.

  • That's right.

  • And the pituitary gland is called the master gland

  • because from the pituitary, we make hormones

  • that work on yet other organs.

  • So I'll give you an example.

  • One of the hormones that's made by the pituitary

  • is called thyroid stimulating hormone, or TSH.

  • And after it leaves the pituitary,

  • it goes into the circulation and it

  • acts on the thyroid gland, 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 triodothyronine, T3.

  • Those would be the two main circulating thyroid hormones.

  • SALMAN KHAN: And what do those do?

  • NEIL GESUNDHEIT: Those regulate metabolism,

  • they regulate appetite, they regulate thermogenesis,

  • they regulate muscle function.

  • They have widespread activities on other parts of the body.

  • SALMAN KHAN: But it kind of upregulates or downregulates

  • the entire body and the metabolism.

  • NEIL GESUNDHEIT: That's right.

  • So someone with hyperthyroidism would

  • have very high metabolism.

  • You may know the classic picture someone

  • with a high heart rate, rapid metabolism, weight loss.

  • That would be someone with excess amounts

  • of thyroid hormone.

  • And then you see pretty much the inverse picture

  • when someone has a deficiency of thyroid hormone and someone

  • with hypothyroidism.

  • So it's critical to maintain just the right amount of almost

  • all of these hormones, and the thyroid hormones

  • are good examples of this.

  • But the ultimate regulation is from that pituitary gland.

  • SALMAN KHAN: This is kind of the master one.

  • It sends a signal there, and then that kind of does the--

  • NEIL GESUNDHEIT: That's right.

  • And we'll talk later about feedback loops,

  • because how does the pituitary know when to stop making TSH?

  • And basically, like a thermostat,

  • it can sense the levels of thyroid hormone.

  • And when those levels are just at the right level,

  • and not too high, it'll decrease the amount of TSH it makes.

  • If the levels are too low, it'll increase

  • TSH to try to stimulate the thyroid gland to make yet

  • more thyroid hormone.

  • SALMAN KHAN: Very cool.

  • And what else do we have here?

  • NEIL GESUNDHEIT: OK.

  • So the other hormones, some of the major ones.

  • The pituitary, in addition to making the thyroid stimulating

  • hormones, it makes a hormone called

  • ACTH, adrenal corticotrophic hormone,

  • which acts on the adrenal cortex.

  • And the adrenal is that gland exactly

  • that sits on top of the kidney.

  • And the outer layers of the adrenal gland

  • are the adrenal cortex, and those are stimulated by ACTH.

  • SALMAN KHAN: And they're not related to the kidney.

  • They just sit on top there.

  • They're structurally there.

  • NEIL GESUNDHEIT: Right They're related only in that sense

  • that the blood supply is rich like the kidneys' blood supply,

  • and they happen to sit above the kidney.

  • And they're called adrenal because they're

  • adjacent to the kidney, which is the renal part.

  • SALMAN KHAN: That should have been obvious.

  • I never realized that.

  • NEIL GESUNDHEIT: But they don't per se

  • filter blood or do any of the key functions

  • that the kidney serves.

  • SALMAN KHAN: I see.

  • And what's their role?

  • NEIL GESUNDHEIT: So the adrenal glands

  • make the adrenal hormones like cortisol,

  • which regulates glucose metabolism

  • and is important to maintaining blood pressure and well-being.

  • And then it makes mineralocorticoids

  • like aldosterone, which is important for regulating

  • salt and water balance.

  • You also have adrenal androgens, which are somewhat important.

  • And those three hormones are the main hormones

  • made by the adrenal cortex.

  • 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.

  • SALMAN KHAN: OK And we have a few more organs here.

  • NEIL GESUNDHEIT: Yeah.

  • So Also add out of the pituitary,

  • we make luteinizing hormone and follicle stimulating hormone.

  • Those would be abbreviated LH and FSH.

  • And those act on the gonads.

  • So in the male, it'll act on the testes, and in the female,

  • it'll act on the ovaries to stimulate

  • the development of sperm in the male and oocytes,

  • or eggs in the female, and also the production

  • of gonadal steroids, primarily testosterone in the male

  • and estradiol in the female.

  • SALMAN KHAN: Right And are we missing anything?

  • NEIL GESUNDHEIT: Well, there are two other hormones

  • that also derive from the anterior pituitary.

  • And those would be growth hormone

  • that's critical for optimal growth of long bones.

  • SALMAN KHAN: The pituitary really does do a lot.

  • NEIL GESUNDHEIT: It does.

  • Yeah.

  • SALMAN KHAN: So it's HGH, human growth hormone.

  • NEIL GESUNDHEIT: Yeah.

  • Human growth hormone, and that would act on long bones,

  • for instance.

  • And then we would have prolactin,

  • which is important in women for lactation,

  • being able to breastfeed after delivering a child.

  • SALMAN KHAN: And insulin is?

  • NEIL GESUNDHEIT: Insulin is key, but it

  • doesn't come from the pituitary.

  • So now we're going to work our way down a little bit.

  • We talked about the thyroid gland making thyroid hormone.

  • And then when you get to the pancreas, which

  • is that yellow structure right in the middle,

  • inside 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.

  • The absence of insulin can produce

  • all of the symptoms of diabetes that we'll talk about later.

  • SALMAN KHAN: It seems just structurally, you

  • have the pancreas right here.

  • You have the adrenal glands right there,

  • that they're all near kind of that interchange on the--

  • because they're all so important to get

  • to where they need to get to.

  • NEIL GESUNDHEIT: That's a good observation.

  • They all have a lot of venous drainage from them

  • so that when they make their hormone,

  • it gets into the bloodstream rather quickly because they

  • are vital structures.

  • SALMAN KHAN: Very cool.

  • So I think we can leave it there.

  • And in the next video, you have some pictures

  • that I think will be pretty interesting.

  • NEIL GESUNDHEIT: OK.

  • Yeah.

  • In the next video, we'll talk about how

  • you have to the right amount of the hormone or else things