If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

Main content
Current time:0:00Total duration:10:56

Video transcript

hormones those things that make teenagers moody miserable and they cause growth spurts and acne that make perfectly normal student totally obsessed with his algebra teacher not that I have any you know real boots-on-the-ground experience with our last one but all that mayhem it's 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 and insects there what stimuli plans 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 endocrine keep the Cribs which is Greek for secretions in and your glands are all over the frickin 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 within 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 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 mono amines 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 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 wilden's 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 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 two lobes which are actually two different glands fused together 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 the way that it interacts for 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 thyroids thermostat it can read how much thyroid hormone is in your bloodstream and when it's levels are low it spits out a tiny bit of thyroid stimulating hormone or TSH which travels to the thyroid the thyroid and turn'd 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 sue 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 I 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 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 I 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 all right 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 to 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 Arlie 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 could you know 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 you know muscular men let's uh let's get back to everybody's favorite topic the gonads sex glands come in two different flavor is not the right word flavors that's bad ok whatever we're just going to go with it where there's the testes and there's the ovaries they get instructions from the pituitary gland to make sex hormones so testes make androgens the main one of these being testosterone which helps with sperm making among other things ovaries make estrogens and progestin to 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 like 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 and someone give 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 are a French embryologist in the 1940s apparently he wondered whether the hormone 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 yeah 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 momma rabbit what jaws 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 pea pea in 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 alert in boys telling the testes to make a whole lot of androgens like testosterone that lower the voice and make a bunch of hair increase muscle and bone mass and encouraged people to do stupid stunts and post them on YouTube and girls estrogens the most important ones being estradiol and progesterone kick off the process of menstruation and breast growth and all that good stuff largely helping the female body get ready to grow in nurse a baby but what we still don't understand very well as 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 Astra Jen 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
Biology is brought to you with support from the Amgen Foundation