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Transcription de la vidéo
- So let's look at the male reproductive system. And so when we learn about the male reproductive system it's useful to actually look at it from two different points of view and so the first view we'll take a look at is called an anterior view. And what that is is basically we take everything in this box here and so what we'll do is -- it's a little bit tough to see there. This is zoomed out. So we'll blow it up for you and that's basically what you see there. And so that's called an anterior view. Looking at it from the front. And that's sort of the opposite to a posterior view which is looking at it from behind. That would be a posterior view. And so there's two points of views like I mentioned. So the other one is called the sagittal view and what a sagittal view is is let's look at this guy over here. Let's say that this is his left side because this is where his left hand is and this is his right side. And so in a sagittal view what you do is you sort of make a cut right down the middle here and you sort of cut away everything on one side. So in this case it would be the left side that we're cutting away because what we want to do and I'll draw the -- I'll draw a little eye here. What we want to do is look toward the right side toward what's remaining on the right side. So we're seeing this cut surface here. And so what that ends up looking like is something like this here and so this is called a sagittal view and to reorient you this here in the background this is the right leg because remember we're looking -- we're looking this way so this ends up being the right leg. So those are the two views that are important when we're learning about the male reproductive system. And actually it's also important to mention that most of what you see here is actually contained within the body so you don't actually see that when you look from the outside. What you do see is just the penis and the scrotum that contains the testes and we'll come to what all of that is soon. Now that we've taken a look at the two different views let's clear away some of this stuff and meet the organs. So the first set of organs we'll look at they're actually paired organs. They're the testes and they're sort of the key organ in the male reproductive system. I'll just shade them in for you here. And the testes are pretty interesting. What happens in the testes is the process of spermatogenesis and so what spermatogenesis is is the creation of sperm and sperm are the male contribution to a baby. So sperm production in the testes has to happen at a certain temperature. It has to be at a temperature that's a bit lower i.e., a bit colder that core body temperature which is pretty warm. And so the testes have to be kept at a temperature that's a little bit lower than body temperature and they do that by hanging out in this -- this fleshy sac outside of the body called the scrotum. And so I'm just pointing at it now. And so this is called the scrotum and the way that the scrotum regulates the temperature of the testes is by sort of retracting upward toward the body if it gets a little bit cold so that they can stay a bit warmer closer to the body or by descending a little bit if it gets a little bit warm and so it does that -- the retracting upward and the descending via two muscles. The first one is called the cremaster muscle -- cremaster -- and the second one is called the dartos muscle. Kind of a cool name. And so those two muscles help to regulate the temperature of the testes so that sperm can be produced. And interestingly there's something called the cremasteric reflex where if you sort of lightly brush on the -- on the upper and inner part of the thigh here on a male instinctively or reflexively rather the cremaster muscle will contract and pull the testes slightly upward on that side. And that's called the cremasteric reflex. Now the testes also have another really important function besides producing sperm and that's the creation of the major male hormone called testosterone. And the testosterone that you produce in your testes is actually responsible for all of your secondary sexual characteristics and when I say secondary sexual characteristics I mean things like hair growth. So when you hit puberty around 12 or 13 years old and you start to produce testosterone in greater amounts you sort of get an outbreak of body hair. So you get hair on your knuckles and on your arms and on your legs and your face and you'll start to grow pubic hair and so testosterone is the main driver of that hair growth. In addition to that you get sort of muscle growth and you also get a deepening of your voice. And so next up what we have is the epididymis and so I'll just color those in. Those sit right on top of the testes on either side. And so the role of the epididymis is to sort of provide a place for the sperm to sort of hang out and develop and so the epididymis is this really long convoluted really wavy set of tubes that sperm sort of spends a lot of time in before it goes off on its journey. And so if you were going off on a journey you'd sort of pack a few things in preparation and sperm sort of do the same thing. And so when the sperm are hanging out in the epididymis they gain more mitochondria, the organelle in the cell that provides the cell with energy. And so the sperm are about to embark on this huge journey and they have to be ready at basically a moment's notice to sort of shoot out and swim a long way and they're going to need mitochondria because they're going to need a lot of energy. In the epididymis they also develop really long tails called flagella and that sort of helps to propel them on their journey as well. And so from the epididymis sperm sort of drains out of the epididymis and into this tube called the vas deferens and so the vas deferens actually drains the epididymis of sperm and brings the sperm upwards behind the bladder and into the urethra which is the next part of the reproductive tract. Now the vas deferens actually runs within a bundle called the spermatic cord and inside the spermatic cord you actually have an artery that serves the testes and you also have a vein that serves the testes. And so all of that together -- and you have that on either side that's called the spermatic cord and let me just draw one on this side as well. So there's your artery and you've got your vein as well. So before we move on let's just clear off a few things or everything, that's fine too and next we'll talk about the accessory glands. And so what the accessory glands do is basically provide sperm with things that they need along their journey. And so if you were going on a journey you might make a few pit stops at a few shops and pick up some things and that's basically what's happening with sperm. And so I'll point out some accessory glands here but before I do that I'll just orient you to where they are with respect to the bladder. And so this yellow object here is the bladder and you can see it on the sagittal view here. And so the first accessory gland that we're going to mention is called the seminal vesicle and there are actually two of them and I'll shade it in here. So on the sagittal view you can see it behind the bladder quite nicely and on the anterior view you have to sort of imagine that it's behind the bladder in there and about there. And so those are the seminal vesicles. And what they do their contribution to sperm is a lot of fluid and in fact they actually make up 60% of semen volume and just to hammer out some terminology here semen is different from sperm in that semen equals sperm plus the fluid that it picks up on the way from the accessory glands. And so the fluid that the sperm pick up from the seminal vesicles is actually somewhat alkaline. And that's to neutralize the somewhat acidic environments of the male's own urethra and the vagina where the sperm will end up and to be alkaline that just means that your pH is greater than 7 which is what water is. The fluid is also rich in fructose and that's so that the mitochondria have sugar that they can use to produce ATP and ATP is what the sperm use for energy to complete their long journey. Now the other two accessory glands are called the prostate gland and the bulbourethral glands and there are actually two bulbourethral glands, one on either side of the penis. These three glands actually contribute more fluid to semen. The prostate gland actually makes prostatic fluid and that increases the mobility of sperm once it reaches inside the vagina and the bulbourethral gland sort of just makes a thick lubricant for both the urethra and the vagina. Now semen actually travels through a tube called the urethra which you can see here in red to get to the outside of the body and it travels through the urethra through the penis which is here in purple blue and so in reproduction the role of the penis is to actually penetrate the vagina so that sperm can be deposited inside.