Great glands – Your endocrine system | Crash Course biology | Khan Academy

– Hormones, those things that make teenagers moody and miserable and they cause growth spurts and acne and they 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 multi-cellular organisms produce one kind or another. For instance, hormones regulate
the process of metamorphosis in insects, 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 and 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 system 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. As you can tell by the name, they send stuff outside of the body, whereas endocrines keep the crines, which is Greek for secretions, in. And your glands are all
over the freaking 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 the 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 in a
small region of 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 signals 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. There’s the 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 the
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 the 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, 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 legwork done. The pituitary is connected
to the hypothalamus, the part of the brain
that acts as the 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 two 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. One 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 that 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 secretion is a signal to secrete less of it, and that’s a 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. Want to 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 freaking 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. And like 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 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 gonna 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 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 Hos, 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’s too low, your pancreas has got your back there too. Say you’re in a push-up
contest with Christian Bale, you’re going to lose,
but you’re going to try. And the 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
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 fla, that’s not the right
word, flavors, that’s bad. Okay, whatever, we’re
just gonna 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 does 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 kinda true. It turns out that why
we’re either male or female has a lot to do with hormones. And someone get me a chair so I can tell you how we know that. Back in the 1940s, French
embryologist Alfred Jost was studying sex
differentiation in bunnies because that’s what you do when you’re a French embryologist
in the 1940s 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 pee-pee
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 ones 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, for example,
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.

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