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

Testosterone

Created by Vishal Punwani.

Want to join the conversation?

  • spunky sam blue style avatar for user michaelamartinez448
    Which anterior pituitary hormone stimulates the release of testosterone?
    (9 votes)
    Default Khan Academy avatar avatar for user
    • piceratops seedling style avatar for user JP
      After receiving signals from the hypothalamus (GnRH), the anterior pituitary releases FSH and LH; the latter causes the interstitial cells (of Leydig) to release testosterone.
      (1 vote)
  • blobby green style avatar for user Mahmoud Magdy
    Why is testosterone in need of a carrier protein ? I mean isn't it a lipid hormone, it can just diffuse though the cell surface membrane and to the nucleus ?
    (6 votes)
    Default Khan Academy avatar avatar for user
  • male robot hal style avatar for user Olaf Tomala
    What is the role of testosterone in females?
    (5 votes)
    Default Khan Academy avatar avatar for user
    • female robot grace style avatar for user Anna
      Testosterone conveys powerful anti-aging effects. It turns fat into muscle, keeps skin supple, increases bone mineral density, puts women in a positive mood and boosts the ability to handle stress. Testosterone also supports cognitive functioning and keeps the liver and blood vessels clean.

      So testosterone acts sort of like ppar delta which is a molecule that affects the DNA expression inside muscle cells to burn more fat for the same amount of work.

      However there is a bad side to giving females testosterone for these effects. It inhibits female processes like menstruation and ovulation which require estrogen(of which there are 3 types) and progesterone.
      (7 votes)
  • leafers seedling style avatar for user Hetakumari Piludaria
    Females also have testosterone, is this the reason why do some female does possess facial hairs and broad shoulders ?
    Females do not have testis so how come they have testosterone ?
    (2 votes)
    Default Khan Academy avatar avatar for user
  • piceratops seed style avatar for user Ahmed Yasser
    does ejaculating or sex uses testosterone? and will having too many of them will make the body stop producing it or even drop its level severely ?
    (1 vote)
    Default Khan Academy avatar avatar for user
    • piceratops seedling style avatar for user Usama Malik
      There is no relationship between Testosterone and ejaculation. Even though, there have been studies where abstinence does lead to higher testosterone levels, ejaculation does not lead to higher or lower blood testosterone levels. Your body is constantly producing sperm and ejaculation would actually lead to increased spermatogenesis (sperm production). Your body is constantly working to replace old sperm cells by creating new ones.
      (5 votes)
  • leaf green style avatar for user dinesh.c.upreti
    Does testosterone enter through a cell membrane by osmosis ?
    (1 vote)
    Default Khan Academy avatar avatar for user
  • starky sapling style avatar for user barbagewillbebarbage
    Does testosterones in transgender people flow through or travel in the body the same? Whether it be injected or consumed, it begins to do the same thing, right? (Just not being produced from the testes obviously!)
    (2 votes)
    Default Khan Academy avatar avatar for user
  • blobby green style avatar for user 😊
    you say that testostrone are present in both male and female
    what is the function of these harmones in female
    (2 votes)
    Default Khan Academy avatar avatar for user
  • female robot ada style avatar for user jeffviberg
    So if a girl would exercise and you would give them testosterone pillers they will be able to get more muscles ? Or is there any contraindications of taking it ? Just regular Testerone you can buy in a fitness shop.
    (1 vote)
    Default Khan Academy avatar avatar for user
    • male robot johnny style avatar for user Finn
      Exercise stimulus and sufficient protein & energy intake are the biggest factors in developing a muscular physique though androgens, such as testosterone, do promote the process of muscle development in both sexes. Testosterone does not annihilate the female reproductive system reliably and hence does not serve as a contraceptive. Once the breasts have developed the fat tissue may atrophy but they cannot be "lost" completely without surgery as the ducts are distinct, differentiated structures in the subcutaneous layers. Testosterone will not cause significant apoptosis/necrosis of these structures.
      (2 votes)
  • male robot johnny style avatar for user sach10thdecay
    in which area of testis the leydig cell exactly prsent and how the formation of testrosterone goes with in it?
    (1 vote)
    Default Khan Academy avatar avatar for user

Video transcript

- Let's meet testosterone. We produce chemical signals in our bodies that allow one part of our body to communicate with other parts of our bodies, and these signals are called hormones. Testosterone is one of these hormones. So testosterone is produced by our testes here. So let me draw a zoomed in view of one testis. And after the testes make testosterone in cells that they have called Leydig cells, that testosterone is transported to other parts of the body via the bloodstream. So I'm drawing red blood cells in red, and I'll show you the little molecules of testosterone in green. And these blood vessels carry testosterone all over the body so that it can carry out all of its biological functions. So let me just point out that testosterone isn't only produced in men. It's actually produced in men and women, but males past the age of puberty, about 12 or 13 years old, have about seven or eight times the testosterone that women of the same age as them do. So we still refer to it as the primary male sex hormone. And to clarify, I'm just calling it a sex hormone because it's produced primarily by some of the male sexual organs, i.e., the testes. So I've told you that it's made in the testes and that it travels around in the blood vessels to every part of the body, but once it gets to its target, what exactly happens? How does it work? So to show you this, I'll blow up a little cell here in the thigh. So here you have a cell, and up here, or lining the cell or just beside the cell, you have that bloodstream that the testosterone is floating around in. And so I'll draw back in those red blood cells, and let's just say the blood is going that way, and here's our testosterone. So when testosterone sees a cell that it wants to enter, it crosses through the cell membrane, which is sort of the cell's barrier to things outside the cell, almost like a selectively permeable gate, and once the testosterone gets inside the cell, it sort of meets this carrier protein, and the carrier protein is something that will bind the testosterone and take it to its next destination within the cell. So we'll draw that carrier protein as a taxi. We have testosterone sitting right here in the backseat of the taxi, and then that carrier protein just drives it a little short way to something called the nucleus. And the nucleus contains our DNA, and those are the blueprints of how we're made. So in red I drew a specific part of our DNA called a gene, and our DNA is made up of millions of genes. So genes are little segments of the DNA, and some hormones interact with our genes to change our characteristics. So that's exactly what testosterone does. It jumps out of the cab, once it gets into the nucleus, and it sort of binds onto that gene. I'll just label that that's a gene. And when testosterone binds the gene, it's able to influence its function. So, for example, if the gene told the body to make more muscle, then testosterone interacting with that gene would increase the rate of muscle production, and, in fact, that is one of testosterone's functions, and we'll touch on that a little bit later. Now, one more note on this topic. Depending on the type of cell that testosterone enters, it can be converted into a different hormone before going to the nucleus to interact with a gene. So the two possibilities are dihydrotestosterone or DHT and estrogen, and that may sound a little counterintuitive, because I think most people think of estrogen as a female-only hormone, but actually males need estrogen as well, and we have a little bit of it, and it comes from testosterone. And even in the female, testosterone is converted to estrogen, and that's how estrogen is made. It just happens a lot more often in the female. Having said that, in men only about 7% of testosterone is converted to DHT, and less than 1% is converted to estrogen. So it's primarily testosterone that's exerting all of the hormonal effects. You're probably wondering what some of the roles of testosterone are. So let's cover those. So testosterone actually starts working when you're really young, when you're still in development in your mother's womb, and what it does there is it induces your reproductive organs to differentiate into male reproductive organs. Because when males and females start out in development in the womb, they have the same precursor reproductive structures, and so the presence of testosterone actually pushes the reproductive organs to turn into masculine ones. Another really important thing testosterone does is, you remember how we said that testosterone is made in the Leydig cells here, and the Leydig cells are one of the cells in the testes? When testosterone starts to be released in higher quantities from those Leydig cells, once you hit puberty around age 12 or 13, that testosterone signals other cells in the testes to start the process of making sperm, a process called spermatogenesis. After sperm production starts, having a baseline level of testosterone in the testes keeps sperm production going. So these are the major functions that testosterone has on the male reproductive tract. But testosterone actually has a lot of other functions around the body. It's responsible for what we call secondary sex characteristics, and these are just physical traits that we typically think of being masculine or feminine. For example, it stimulates the growth of facial hair, armpit hair, pubic hair, and hair on your arms and legs and your chest, just to name a few areas. It's also responsible for the deepening of your voice that happens as you develop as a male, and that happens because testosterone induces growth of the voice box or the larynx, and some people know that as the Adam's apple. That's why you see a prominent sort of bulge in the throats of males. Another thing it does is it induces male-pattern fat distribution. And so, that's sort of fat distribution around the central part of the body. It also has some structural affects on our bodies. So it stimulates the process of anabolism, and what that means is taking smaller components in our bodies, like proteins, and building them up to bigger components or aggregates of those components, like muscles. So muscles are basically a big aggregate of proteins. That e.g. just means for example. Testosterone also stimulates bone growth. So it'll make your bones bigger in diameter and longer, but it also stimulates the termination of bone growth once your bones can't grow anymore. So those are the major secondary sex characteristics that testosterone stimulate. It affects your behavior, increasing your sex drive, and has been thought to possibly cause higher levels of aggression. Testosterone can increase the number of red blood cells that we have, and it does that by stimulating our kidneys to produce another type of hormone called erythropoietin or EPO, and EPO's role is to cause the creation of more red blood cells. So that all sounds pretty awesome, right? Well, except for maybe the possible link to aggression. But it turns out there's a limit to the testosterone that you want floating around in your blood at any given time. If you have too much, bad things can start to happen. It's been theorized that the prostate has cells that are stimulated by DHT or dihdryotestosterone. Do you remember that metabolite of testosterone we talked about earlier? And so, the idea is that they grow bigger when there's too much DHT around and increases the risk of developing prostate cancer. The jury's still out on that one, though, but one thing we do know is that male-pattern baldness, that is, baldness on the top of the scalp, is actually promoted by excess DHT in the blood. So this tells us that we don't want too little or too much testosterone traveling around in our blood and affecting our cells. So, how do we control how much testosterone is in our body? Well, it turns out that testosterone, to a large extent, self-regulates how much is produced. But how can it do that? It actually does that through something called a feedback loop, and this concept of the feedback loop is by bar how most hormones work. So again, a feedback loop is a method of self-regulation. So an example of a feedback loop would be something like a thermostat. Let's say you set the temperature in your room to a nice 25 degrees Celsius. So let's say it's 20 degrees in the room now. The thermostat will sense the temperature of the current air in the room and heat the room another five degrees, until it gets to 25 degrees. And once it's sensed that 25 degrees has been reached, it will turn off the thermostat. And testosterone in the body's regulated in a similar way. There's a part of the brain called the hypothalamus that acts similar to that thermostat. It's actually sometimes referred to as the body's thermostat, because it regulates most of our feedback loops, and the testosterone feedback loop is one of them. So the hypothalamus will sense the amount of testosterone that's floating through your blood. If it's not enough testosterone, the hypothalamus will send a signal to another gland in the brain, called the anterior pituitary, and that actually just sits right underneath the hypothalamus, and then the anterior pituitary sends more hormones to the testes that increases their testosterone production. Conversely, if there's too much testosterone in the blood, the hypothalamus will sense that, and it will stop sending signals to the anterior pituitary, and then the anterior pituitary will stop sending signals to the testes. And so, when that happens, you actually get a decrease in testosterone. So overall, this negative feedback loop is used to control the amount of testosterone in the blood, and that control of blood testosterone levels is actually referred to as testosterone homeostasis, homeostasis meaning to remain constant. And that's testosterone.