Great Glands – Your Endocrine System: CrashCourse Biology #33

Great Glands – Your Endocrine System: CrashCourse Biology #33


Hormones! Those things that make
teenagers moody and miserable, and they cause growth spurts
and acne, and they can make a perfectly normal student totally
obsessed with his algebra teacher. Not that I have any real, boots-on-the-ground
experience with that last one. But all that mayhem is just
the handiwork of your sex hormones. The fact is that there
are more than 50 different kinds of hormones coursing
through you right now, and all multicellular organisms
produce one kind or another. For instance, hormones regulate
the process of metamorphosis in insects, and they’re what
stimulate plants to grow and fruits to ripen. In animals, the network that
makes and releases hormones, your endocrine system,
is one of the two ways, along with the nervous system,
that important information is communicated from one
part of your body to another. Right now, your endocrine
system is spraying hormones into your bloodstream that
are doing all kinds of things all over your body:
giving instructions to other glands, regulating the levels of salt,
sugar and water in your blood, telling your heart to beat faster, and, yes, they’re partly
responsible for that daydream you may or may not be having
about Taylor Lautner right now. But keep your eye on the prize here! We’re doing science! Pay attention! The endocrine system and the
nervous systems both carry information around the body,
but while the nervous system carries information really
quickly and the responses are usually short-lived,
endocrine responses take a while to get going, but their effects
can last for hours or even weeks. The word hormone comes from the
Greek for “to arouse activity,” and they’re secreted
by endocrine glands, the series of organs
that also manufacture them. In addition to endocrine glands,
you also have exocrine glands like salivary glands
and sweat glands, and as you can tell by the name,
they send stuff outside the body, whereas endocrines
keep the “-crines,” which is Greek for “secretions,” in. And your glands are all
over the freakin’ place: Some of the heaviest hitters
are in your brain, but you also have them in your
throat, right over your kidneys, right below your stomach, and of
course in your baby-making areas. All glands have blood vessels
coming from them so that hormones that they release can get
into the bloodstream fast. And many of your hormones
circulate through your whole body, only binding to the
cells that have the right receptor proteins that fit them. But there are some
hormone-driven messaging systems that are more localized. For instance, paracrine signaling
releases hormone molecules that degrade really quickly
and are only received within a small region in the body. Example: testosterone, manufactured
by the testes, tells the testes how many sperm they need to
be making right this second. And to see hormones work
on an even smaller scale, get a load of autocrine signaling, which sends chemical
messages within a cell, or from one cell to the
adjacent cell, at most. This is what happens in your
immune system when a single T-cell realizes it needs to
start cloning itself so it can fight off a virus. Your cells receive hormones
through signal receptors, but how and where a
hormone binds to its receptor depends on what kind
of hormone it is. There are three different types:
steroids, which do a lot more than make your muscles big and
get you all angry and stuff. Steroids are derived from cholesterol and there’s a bunch of
different types of them. There are peptides, which are
just chains of amino acids. And monoamines, which are based
on a single amino acid. The only really important thing we
need to keep straight about these is that peptide and amine
hormones are water-soluble and don’t dissolve in lipids. And since cell membranes
are made of lipids, those hormones can’t
pass into a cell. Instead, they bind with receptors that are on the surface of the cell. But steroids are lipid-soluble,
so they’re able to penetrate the membrane and bind with
receptors in the cell’s nucleus. Using these methods, the endocrine
system sends out all kinds of important chemical bulletins,
many of which start up in the brain, in a tiny gland about
the size of a pea. The pituitary gland. The pituitary gland,
it’s the master gland, the Napoleon of the endocrine system. Except that Napoleon actually
wasn’t very small, that’s a myth, but you get what I’m saying. The pituitary gland makes
hormones that instruct other glands to make other hormones, and those hormones actually
get the real leg work done. The pituitary is connected
to the hypothalamus, the part of the brain
that acts as a liaison between the nervous system
and the endocrine system. So a big part of its job is to
tell your glands what to do based on information it gets from your
senses and other nerve functions. For example, breastfeeding women
will start releasing milk when their baby starts crying. Sensory information,
in this case auditory, comes to the hypothalamus from
the nervous system telling it that there’s a little snuggle of
baby nearby that might be hungry. This causes the hypothalamus
to nudge the pituitary gland, which in turn releases hormones that stimulate milk production
and secretion. Pretty cool! The pituitary gland sits directly
underneath the hypothalamus and has 2 lobes, which are actually two
different glands fused together. The posterior pituitary is an
extension of the hypothalamus and it secretes two hormones that are
actually made by the hypothalamus. On of them is oxytocin, which
stimulates contraction of the uterus during childbirth and
helps with breastfeeding, but it probably also has a role
in things like social recognition, pair bonding, orgasms, and anxiety.
Which is interesting and weird. And the other hormone secreted by
the posterior pituitary is antidiuretic hormone, which tells
the kidneys to retain water. The anterior pituitary on the
other hand both manufactures and secretes a
whole battery of hormones and one of the places these
hormones end up is the thyroid. The thyroid regulates your
metabolism, your appetite, muscle function, blood pressure,
heart rate, among other things, and the way it interacts with
the pituitary is a good example of a negative feedback loop, a method
of communication that’s common all over the body, and especially
in the endocrine system. Basically, the pituitary is
like the thyroid’s thermostat. It can read how much thyroid
hormone is in your bloodstream, and when its levels are low,
it spits out a tiny bit of thyroid-stimulating hormone,
or TSH, which travels to the thyroid. The thyroid, in turn,
secretes thyroid hormone which boosts our metabolism. And that increase in
metabolism tells the pituitary to stop sending out TSH. So the effect of the
pituitary’s secretion is a signal to secrete less of it,
and that’s the negative feedback. Other glands that are
controlled by His Royal Highness the Pituitary Gland
include adrenal glands. These guys sit right on top of
the kidneys and are in charge of making hormones that help the
kidneys maintain the level of salt and water in your
body, but they also, you may have heard,
respond to stress. Wanna see how it works? Well, let’s say you’re walking
down the street minding your own business and you get
hit in the face by an angry duck. Let’s say that this
is unusual for you, and you don’t know what’s going on, just that you’re being
attacked by something. As soon as the sympathetic
nervous system senses that something potentially
dangerous is happening, the hypothalamus tells the
pituitary gland to secrete adrenocorticotropic hormone,
or ACTH for those of us who don’t have all freakin’ day. This stimulates the adrenal
glands to make epinephrine, also known as adrenaline. Now, the epinephrine in your
bloodstream will tell a bunch of different organs to do a bunch
of different things, all at once: cut off blood supply to your
digestive system, send a bunch of blood to your lungs and muscles,
and speed up your heart rate. All to help you on your quest
to vanquish this dastardly drake. Unlike pretty much every other
muscle contraction in your body, your heart is controlled
by the endocrine system, as well as your nervous system! You may have noticed
that after a scare, your heart races for a
couple of minutes afterwards? That’s because the epinephrine
is still in your bloodstream, telling your heart
to race like crazy, even after you’re no longer
in mortal danger or whatever. Alright, I know you’re wondering when
we’re going to get to the gonads. But let me warm you up first
with the function of your pancreas. Super sexy gland,
the biggest in the body. I’ve mentioned a couple of times
that glands regulate the balance of solutes in your blood: This is one of the most
important things that the endocrine system does, and no one
does it better than your pancreas. Because its job is to regulate the
levels of glucose in your blood, and since glucose is
what makes cellular respiration, and therefore, your life,
possible, this is important. When the concentration
of blood glucose rises, say after you eat a
couple of Ho Ho’s, the pancreas secretes
insulin into the blood. The insulin then
travels around your body and stimulates pretty much every
type of body cell to absorb glucose. Liver and muscle cells convert
the glucose to glycogen for storage, and other cells
in the connective tissue called adipose cells
convert the glucose into fat. But if your blood sugar is too low, your pancreas has got
your back there, too. Say you’re in a pushup
contest with, Christian Bale. You’re going to lose,
but you’re going to try. And trying, is going to
require quite a lot of energy. Your friendly pancreas will
release another hormone, glucagon, which stimulates the liver
and muscles to start the process that breaks up the glycogen
and fat to release the glucose, so that you can lose
to Christian Bale. But you know, losing to
Christian Bale is better than winning against most people. Alright, so now that
we’re back to muscular men, let’s get back to everybody’s
favorite topic. The gonads! Sex glands come in
two different flav- That’s not the right word. Flavors? That’s bad. Ok. Whatever.
We’re just going to go with it. There’s the testes and
there’s the ovaries. They get instructions from the
pituitary gland to make sex hormones. The testes make androgens, the main
one of these being testosterone, which helps with sperm-making,
among other things. Ovaries make estrogens and
progestins which stimulate the growth of the uterine lining
and some other stuff. Like what other stuff? Well, you might think that your
biological sex is determined by the parts that you have.
But that’s only kind of true. It turns out that why we’re
either male or female has a lot to do with hormones. Someone get me a chair.
so I can tell you how we know that. Back in the 1940’s French
embryologist Alfred Jost was studying sex differentiation in bunnies
because that’s what you do when you’re a French embryologist
in the 1940’s, apparently. He wondered whether the
hormones secreted by the gonads during embryonic development
had anything to do with whether a bunny embryo turned out
to be a boy or a girl. So he very carefully,
very, very carefully, and this is a little disturbing, removed bunny embryos
from their mother, and then, also very carefully, removed the part that would
become the ovaries or the testes from the bunny embryos,
and then, also very carefully, he put the embryos back
in the mama rabbit. What Jost found after the
bunnies were born was that the ones that he performed the
surgery on turned out to be girls. So, in the absence of gonads,
and therefore hormones that specifically instructed
the development of testes and the growth of a peepee
and a deep bunny voice, he discovered that
the default setting for mammalian embryos
is Make it Female. So, sex hormones are hard at
work even during fetal development to make us who we are. But they’re SUPER hard at
work during puberty, when the pituitary gland puts
the gonads on red alert, in boys telling the testes to
make a whole lot of androgens like testosterone that lower the
voice, make a bunch of hair, increase muscle and bone mass, and encourage people to do stupid
stunts and post them on Youtube. In girls, estrogens, the most
important one being estradiol and progestins, like progesterone,
kick off the process of menstruation and breast growth
and all that good stuff, largely helping the female body get
ready to grow and nurse a baby. But what we still don’t
understand very well is how sex hormones affect our emotions. We do know that, for instance,
that estrogen is required for the manufacture of serotonin,
the neurotransmitter that gives us a sense of calm and well-being. So when estrogen levels
drop quickly during a woman’s menstrual cycle,
it can make her feel off kilter. But the effects of sex hormones,
not just on our bodies, but our minds remains
a significant mystery. Which is good, because I
don’t want to even go there. Thank you for watching this
episode of Crash Course Biology. Table of contents over there
if you want to revisit anything. Thanks to everyone who helped
put this episode together. And if you have any questions
for us, there’s Facebook, there’s Twitter, and of course,
there’s the comments below.

100 Replies to “Great Glands – Your Endocrine System: CrashCourse Biology #33”

  1. LOL, This is my first time commenting on a youtube video, I just couldnt let it go.

    I watched this video out of interest, I have got to say this guy is the funniest lecturer I have never ever ever ever ever met. you too good man, I got myself watching this whole video even though I am writting an entirely whole lot different module exam tomorrow. BIG UP

  2. Your videos are the best! I'm in pharmacy school and it's my for sure go to when I don't understand something with A and P. Thanks

  3. this is the greatest thing ever. I love learning about the body. And this does it so fast, so succinctly, and so clearly.

  4. Explanation stays in mind for long time if we read the once nd take notes once it will be enough such a effective video this is nd vry informative v can implement these teaching methods and gestures thank you

  5. @crashcourse do you plan on redoing these videos once the pop culture references become obsolete? like maybe now?

  6. Epinephrine/adrenaline release from the adrenal glands during a 'fight or flight' situation isn't mediated by ACTH (this would take far too long for it to be effective). The message comes via the sympathetic nervous system which directly innervates the adrenal medulla. Once a dangerous situation is detected by the brain, impulses travel through the SNS straight to the adrenal medulla which then releases a heap of adrenaline into the bloodstream. Resulting in an almost immeadiate response – increased heart rate/respiration rate/blood pressure, dilation of the pupils etc.

  7. you know how he said that the mother hears the baby crying? what if the mother is deaf and/or blind??

  8. Hank, you're the funniest, most entertaining and information loaded teacher ever ๐Ÿ˜‚๐Ÿ˜๐Ÿ˜๐Ÿ˜

  9. I mean, he kinda gets on my nerves but at least he gives examples of a function or type of tissue unlike many teachers in this dingus field. ๐Ÿ˜š

  10. So without the presence of testosterones or removal of male gonad making cells at embryonic stage, a being can become female, despite having XY chromosomes?

  11. Hey Hank, what happens when there is something wrong with the pituitary gland? For instance it isn't receiving all the commands it's given?

  12. At the end when he was talking about how woman are moody during their menstrual cycle i was like "yeah I wouldn't suggest messing with a woman that's on her period, it's a bad idea"

  13. all this… and cant even figure out why people go bald aside from genetics lol. seriously though.. wonderful crash course!!!!

  14. 3:36 ุดูˆ ุจูŠุนู†ูŠ ู‡ุงู†ูƒ ๐Ÿ˜…

  15. Table of Contents

    1) Signalling Systems 2:07
    2) Pituitary 3:19
    3) Hypothalamus 4:17
    4) Thyroid 4:52
    5) Adrenal 5:38
    6) Pancreas 6:51
    7) Biolography 8:49

  16. okay so here 's the thing
    we have test every week and so the first 2 weeks i studied notes and powerpoints and almost failed the test.
    but than the 3rd week i only watched crashcourse videos and got 90%.

  17. Good video; could have used a half-sentence shoutout to the existence of intersex people when discussing sex organs, but it's a short video so the lack is certainly understandable

  18. People who make this videos are illuminatis the title four kingdoms mean the idol that showed up in Kingโ€™s dream in the Bible, they represent this world, opposite from the kingdom of God.

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