Wk 7a Male reproductive system

he male reproductive system in quite a lot of detail. Look at the anatomy and then we'll look at the physiology. So by the end of this session, you should be able to describe the anatomy and physiology of the male reproductive system and the process of male sperm formation. So we're going to look at the A and P of the external genitalia, the A and P of the internal male genitalia, the physiology of erection, ejaculation, resolution and refraction. So in order to study this, you can look at chapter 18 in the Ross and Wilson textbook and then there's some clinical conditions and review and revision questions as well on this topic. So do make sure that you engage with those materials to marry up with what we're learning in this lecture. So there's some different information I'm going to be presenting to you and some stuff in Ross and Wilson that you need to read about. So let's start then with the anatomy of the male reproductive system. We separate it into external and internal parts. So the external genitalia is the penis and scrotum and the internal genitalia is quite complex, lots of tubes. We've got two testes, so plural testes or one testis, including the epididymis, which sits on the top of that. There are two spermatic cords, two ductus deferens, or you may have learned that as the vas deferens, that lead from the testes up into the pelvic cavity. We have two seminal vesicles, two ejaculatory ducts, one prostate gland and one urethra, which of course has dual purpose, both in the urinary and the reproductive systems. So we're going to orientate ourselves to this fairly complex anatomy. So we've seen this image before, just a little reminder of the urinary system in the male. So here is the bladder, sitting in the pelvic cavity usually. And coming from the bladder, you can see that we have the urethra, all right? So this is the urethra. You can also see some of the structures of the reproductive system, which we'll talk about in a minute. But in terms of the urinary system, we've got the bladder, the urethra that passes through the prostate gland, which is here, the urethra that passes through the pelvic floor muscles, which is here. And then we've got the urethra that comes through the base and the body and the shaft of the penis and then out. So we've got two ureters entering the bladder posteriorly, we've got the central bladder and then we've got the long and curved male urethra. So the urethra, therefore, has different sections depending on what it's passing through. So the first part of the urethra, immediately as it leaves the bladder, is the prostatic urethra because it goes straight through the prostate gland. The second part is the membranous urethra, and that's the part that passes straight through these pelvic floor muscles. That's the membranous urethra, and of course that's only a very short distance. Before we get to the spongy urethra, and this is the spongy urethra passing through from the base, through the body and shaft of the penis. So the deep transverse muscle goes from the pubic symphysis to the coccyx. Those are the sort of pelvic floor muscles through which this membranous urethra passes. And I'm making a point of it because this is where urinary control comes in. Conscious urinary control in the male comes through the sphincter here. So it's this pelvic floor muscle that helps maintain the continents of urine in this region. So that's called the external urethral sphincter. So there is the external urethral sphincter, and you might remember that the internal urethral sphincter is actually as it leaves the bladder. So there's internal, there's external. So I think we've covered all of that. That's just to give you a diagram that gives you all the labels in case you missed some of that. So we're going to move on from the male urinary system and now look in detail at the male reproductive system. So the external genitalia, as we mentioned, was the penis and the scrotum. So we've got the sort of shaft of the penis, and we've got the end of the penis known as the glans penis. And that's covered with a sort of a thin skin layer, which is known as the foreskin. And then sitting immediately posterior to that, we have the scrotum or the scrotal sac, and on either side that contains a testes. So these are the external genitalia, the penis and the scrotum. So the testes is the first of the internal genitalia in the male, and it's a homolog of the ovary in the female. So this is where the sperm is produced, and this is the site of testosterone production as well in the testes. And I'm sure you're aware of the fact that the testes have to be outside of the body because in order to maximize sperm production for sort of healthy sperm, you need to have a body temperature or a temperature environment two to three degrees Celsius lower than internal body temperature. So that's the reason as to why the testes are outside, if you like, of the pelvic cavity. Even though they're internal genitalia, they're outside of the pelvic cavity, unlike the ovaries, of course, which we know are sort of much higher up. So beyond the testes, we have this structure known as the epididymis, and you'll see there's a head of the epididymis that sits right on the top of the testes, and the tail of the epididymis comes posteriorly around the back of the testes, and then you'll notice that there's a tube coming directly from that. So the epididymis is like a sort of maturation school for sperm. This is the area where newly made sperm are going to be stored until it's time for them to be ejaculated. So that's the function of the epididymis, is a good site for maturing sperm to be stored prior to ejaculation. And then the connecting tube between the epididymis and the urethra is this very long tube here known as the vas deferens, or the ductus deferens. So this is the ductus deferens, it comes from the tail of the epididymis, and it reaches up through, sort of posteriorly, through the scrotum, and then up into, via the spermatic cord, up into the pelvic cavity, and it carries quite a sort of an arching core, so you'll notice it goes over the top of the ureter, alright, goes over the top of the ureter and to the back of the bladder, where it will then join up with this structure here, which is known as the seminal vesicle. So we have two of those, one on the left, one on the right. So this now is the seminal vesicle. And the two combine at what's called the ejaculatory duct, this is the ejaculatory duct where we have the vas deferens or ductus deferens and seminal vesicle coming together, and then away this goes through the prostate gland, and then we join the urethra at this point. Alright, so as the urethra passes on, so we see the addition of a bulbo urethral gland, so that's sitting within that pelvic floor muscle, and this is glandular tissue that's going to provide sort of mucus, if you like, to lubricate the inner lining of this urethra, and this helps the sperm to sort of project its way rapidly through the urethra and then out. So those are the bulbo urethral glands sitting within that muscular structure there. And then, as we know, that's the external urethral sphincter, and then we move on into the male urethra and then out at the end. So that's sort of, in a nutshell, the male reproductive system that we've seen in that longitudinal section. So there's plenty of new structures and new names to make sure you know the names of the different ducts and the different glands, so there's lots of different things happening at different times, so you need to be able to articulate what those are. So we've learned about the testes, the spermatic cords we'll talk about in a little bit more detail in just a moment, but we learned that the ductus deferens passes through the spermatic cord and into the pelvic cavity. We've learned about the epididymus that sits over the top of the testes, the ductus deferens that goes into the pelvic cavity. We've learned about seminal vesicles, ejaculatory ducts, bulbo urethral glands, the prostate gland, and the urethra. So in your shoes what I would do is, in a couple of days, maybe print this image off or just look at it and see if you can label it for yourself so you're nice and familiar with all those different structures.

If we were to then have a look at the male reproductive tract from behind, this is a posterior view with lots of these sort of external tissues removed, you can see hopefully that we've got the testes here with the epididymus, we've got that ductus deferens, and I'm just showing you again that it goes up and over the front of the ureter before it joins with the seminal vesicle. So this structure at the back of the bladder is really quite complicated. You've got the ductus deferens coming round, you can see it widens a little bit into an ampulla, and then we've got this important tubular connection with the seminal vesicle both on the left and the right side. So you've got lots of ducts all coming together at this one point at this is the ejaculatory duct on the left side and the right side, and then these will feed into the prostatic urethra. So I like this image because it shows you exactly where that connection point is, so it's sort of deep within the prostate gland isn't it? And you see there's a little bit of a broadening of the prostate gland here, so the ureter is a little bit wider here, and so this is where sperm will sit just before it's ejaculated, and then off it goes down through the urethra and out.

Bless you. So this diagram again is just labeling all the structures that we've seen before but we're just looking at it from a different view.

Okay so we're now going to talk about the spermatic cords.

So the spermatic cords are really quite complicated structures, it's essentially the connection from all the things that the testes need to keep them alive and keep them functioning and to support the ductus deferens leaving and the veins leaving and the lymphatics leaving. These are these very sort of complicated structures that help supply the testes with everything they need. And just to remind ourselves that the whole point of having the testes sort of outside of the pelvic cavity is in order to maintain a temperature of around about 34 to 35 degrees celsius, which is unlike core temperature which is about 37 degrees celsius, so it's to keep this cooler.

So the spermatic cords, these are these complex anatomical structures that are suspending the testes in the scrotum. So the scrotum is like a protective covering if you like for these very important testes. And of course the testes need to have an arterial supply so they have a testicular artery, there's what's called a pampiniform plexus which is all imported in helping temperature regulation, I'll show you that in a minute. There are testicular veins, there are lymphatics, there's the deferent duct on the left and on the right and there's the thin muscle known as the cremaster muscle which is striated and so that's able to lift the testes when necessary and it's also covered with connective tissues.

So all of these structures extend through what's called the inguinal canal to attach to the posterior wall of each testes. So in this diagram you can see an intact spermatic cord, this is the spermatic cord with all of those complicated structures within it and you can see that it's sort of wrapped around the testes as it's outside of the body. So this is the inguinal canal and then we've got the spermatic cord that then protrudes through that inguinal canal and down into the scrotum.

On this side some of this tissue has now been removed so that you can see the testes, you can see the head of an artery and the artery is surrounded by these veins known as the Pampiniform plexus and this is a really cool way of cooling the arterial blood so that as the artery passes down the cooler blood coming back from the testes is in direct contact with it and it's going to cool the arterial blood as it gets to the testes. So that's quite a sort of a handy little anatomical design so that even when the blood supplies the testes it's already cooler than it was when it was further up.

All right so those are the spermatic cords and this is the cremaster muscle which is striated so it's under sort of voluntary control.

So the layers of the spermatic cord wall, this is the spermatic cord as we've said.

Here's the scrotal sac, something I didn't mention about the scrotal sac is that you can see a sort of a midline division and that's known as the raffae, the midline division between left and right scrotal sacs with the sorry right and left scrotal sacs and so the spermatic cord is equivalent on both sides on both right and left.

So we have this inguinal canal which is sort of where all of these structures have descended during fetal development.

These start to descend and move down through a deep inguinal ring and then they emerge via this superficial inguinal ring so they move down through here. The spermatic cord itself is this whole structure and then there's this external spermatic fascia which helps to sort of cover it and then there's an internal spermatic fascia which is on the inside of that muscular layer.

So the cremaster muscle is skeletal muscle as we've said it's striated and its job is to lift and lower the testes. There is a dartos muscle which is more superficial to that and the dartos muscle its job is to lift and lower the scrotum all right so there's a bit of a difference you can lift and lower the testes independently and lift and lower the scrotum. So as we've learned the testes they descend during fetal life and usually by about 36 weeks of gestation the testes should be oops the testes should be located down in the scrotal sac outside of this cavity all right so full term for a baby boy is 40 weeks same for baby girl but full term is 40 weeks so about a month before birth these testes should already have descended down here. There are some some infants that are born where the testes are undescended and so they may have to have a small procedure to help bring those down into the scrotal sac.

So in terms of the blood supply let's have a little look at the blood supply now we've mentioned it a little bit but let's start right at the very top you can imagine that there's a central abdominal aorta coming down the back of the abdominal cavity and then it separates doesn't it into two it separates into the common iliac artery on the right and on the left and then that will quite quickly divide into two branches again so we have the internal iliac artery that's going off to the genitalia and the external iliac artery that's going off down to the legs so these are the sort of main branches that are going to supply the male genitalia you will also notice that there's a blood vessel here an artery that's coming alongside here and it's going down into the spermatic cord and that's in the male is the sperm sorry that's the testicular artery and that's a branch that comes directly from the aorta but much higher up all right so that the supply to the testes is different than the supply of the rest of the male genitalia all right so the testes have that gonadal artery that's branched from the aorta so you can call it a gonadal artery and then that's the same in males or females but in the male the gonadal artery is called the testicular artery and it's a direct branch from that aorta we've mentioned about the venous drainage and one of the sort of methods of venous drainage is via this pampiniform plexus and we've learned that this is helpful it's a little plexus a little sort of plait that's what plexus means it's like a little plait of venules and veins that are surrounding that artery to help to cool that blood down all right so the arterial blood reaching reaching the testes is cooler than it would have been and then the testicular vein which comes from this pampiniform plexus that connects directly to the inferior vena cava on the right side on the left side if you think about your anatomy of where the inferior vena cava is is slightly on the right hand side so it feeds into the right atrium of the heart doesn't it so in order to get around that the left testicular vein will drain first into the left renal vein and then into the inferior vena cava all right so that's just a little bit of different anatomy between the left and right sides so we've learned that the the arteries supplying the gonads to the testes they have a direct branch from the abdominal aorta we've learned that venous drainage of the scrotum comes via the pampiniform plexus up to the testicular veins and that the right testicular vein drains into the IVC and the left testicular vein drains into the left renal vein first and then into the IVC so this is different to the arterial blood supply to the penis which comes via the pudendal artery and the internal iliac artery so i showed you where that internal iliac artery was that then branches into the pudendal artery and that supplies blood to the penis and penile drainage with veins is different too and that's via the deep dorsal veins and superficial dorsal veins of the penis so we'll we'll have a look at that a bit later on there's also lymphatics and the lymphatics in the spermatic cord they're going to drain upwards and away towards the aorta so now we can talk a bit more about the scrotum so this is a pouch of pigmented skin with a covering of hair so that's homologous to the labia majora in women it's situated below the symphysis pubis which as you remember is where the two pubic bones join right at the front and the scrotum sit directly in front of the anterior thigh and directly behind the penis that raffae is an important sort of central dividing line separating right from left and it has a thin layer of fibrous and connective tissue with a small amount of involuntary smooth muscle and that's known as the dartos muscle and there's lots and very tender and exposed area there are two compartments left and right each containing a testis the left scrotum and testis in men is usually slightly lower than the right and it's thought that that venous connection to the real artery first and then going across to the IVC creates a bit more a backlog if you like of blood which is what causes that scrotum and testis to be slightly lower on the left and the right but it's it's not essential general sensory innovation scrotal sensation comes from the sacral nerves s3 and s4 in terms of sympathetic innovation the sympathetic nerves are controlling that dartos muscle so they are controlling the smooth muscle of the scrotum and this is important for temperature control so for example if a man goes swimming in really really cold water you want to protect the testis from that that cold shock so it will be the sympathetic innovation via the dartos muscle that will elevate the scrotum in that situation if it's if the situation is too hot the dartos muscle will be relaxed and therefore this the testis will drop or the scrotum will drop down further to help keep it cool so we can move on now to the testis or singular testis and we're going to spend a bit of time on this because this is kind of like the business end if you like these are the male reproductive glands they're equivalent to the ovary in the female and these are oval shaped and they sit within the scrotum relatively small they weigh about 10 to 12 grams they're about four centimeters by two centimeters by two and a half centimeters the right testis is often slightly larger than the left i've got no real reason for that and they're surrounded by three tissue layers so at and after puberty the testis are the site of production of testosterone they're producing lots of testosterone during puberty and from there on in the testis of course also the site of sperm production so the sperm have to be produced and they have to mature and they are stored all in the testis all right so we'll learn a little bit about that in just a minute so remember that testis are all about sperm production and that goes that's continuous sperm maturation so in order for sperm to mature properly so that they're good swimmers they have to have a period of time within the epididymis to mature and then they're stored in that epididymis before they are ejaculated or reabsorbed in terms of innovation the testis has a motor nerve supply and so does the scrotum so in sort of general motor innovation it's the chromastomuscle that is important because it's supplied by l1 and l2 it's important for the elevation of the testis this time so chromastomuscle is all about testicular elevation whereas dartos was about scrotal sac elevation so this is involuntary and voluntary control so things like fear and arousal causes contraction and therefore elevation of the testis and we've already talked about the dartos which is different because that is involuntary smooth muscle of the scrotum so this is more about temperature regulation the dartos muscle temperature regulation of the testis so it relaxes when hot and contracts when cold there is parasympathetic innovation too and that's via the pudendal nerve s2 to s4 to the testis and this brings about arousal and erection and we'll talk about that in more detail a bit later on the sympathetic innovation to the testis this is controlling the glandular secretions it also controls ejaculation and orgasm and the dartos muscle for temperature control and again we'll talk about that when we discuss physiology so there's motor parasympathetic and sympathetic innovation as well as sensory innovation to this area so in terms of sensory innovation you may not have seen the skin hence the word dermatome and it's like a little map so the nerves that are detecting sensations around this region have come from t10 so come from the thoracic vertebra t10 just underneath that this area has come from t11 this has come from t12 l1 and so on so in terms of scrotal sensation it's from the sacral nerves in the region of s3 and s4 but the testis sensation is coming from t10 and t11 and so that gives us this sort of sense sensations coming from different nerves and different regions all right so for the scrotum it's sacral and for the testis it's t10 and t11 so much higher up and so that's why sort of kicking the balls for once of a better expression can give abdominal pain because that's coming from much much higher up okay so let's have a look at the testis now we're going to take a testis we're looking at it in cross section we're going to unravel what's going on within the testis themselves and how sperm are produced so the testis are covered in three different layers and they're clinically relevant so from outside to inside we have this tunica vasculosa which sits on the outside and that's got a capillary network and connective tissue to support the testis itself we then have a two layered tunica vaginalis and that's derived from peritoneum of the abdominal cavity and we've got a visceral layer and a parietal layer it's a bit like with lungs you know with the lungs you it's like a balloon being sort of or a fist being pushed into a balloon it creates an outside and an inner layer it's just the same so the visceral layer is closest to the testis the parietal layer is further away from the testis and then we have this all important tunica albuminear so this is the the really important thick white fibrous layer and that's thickest at the back that's known as the mediastinum testis and that brings in the blood vessels the ducts the lymphatics and some nerves they will all enter the testis at this mediastinum testis at the back and this tunica albuminear is going to help sort of the tunica vasculosa is not shown in this diagram but that was the outermost layer then we've got the tunica vaginalis it's got this outer parietal layer then you can see it folds in on itself and that then becomes the tunica vaginalis the inner visceral layer that surrounds the testis itself and then you can see this tunica albuminear that white layer that sits over the top of the testis protecting this incredible tubular network within it so if we have a little look this tunica albuminear not only surrounds the whole testis but it creates these pockets a bit like a segments of an orange i suppose creates these pockets where all these tubular structures are housed and protected and then you'll notice that there's this little connection between all of this busy area here and then this network and then these structures that feed into the epididymis so this structure is really important for developing new sperm and then getting those sperm to the epididymis where they're going to be stored and if we have a look at the architecture of the epididymis you can see this is really really tightly coiled tubes and all those maturing sperm are going to be stored okay so those are the three layers of the testis so we've learned that this tunica albuminear is a really important structure because it's surrounding the testis giving it some support and it's projecting internally separating those little tubules into various septa all right so these septa subdivide the space into about 250 lobules so each one of these is a lobule this is a septa it's a dividing wall isn't it so each lobule contains up to four convoluted seminiferous tubules and it creates a protective blood testis barrier so that's protecting these all important very delicate sperm from the man's protects from any toxins in the blood etc and it modifies how much glucose is made available to the cells so it's really creating a protective environment for sperm production so we can move on then and just have a little look at some of the labels we've seen there's a septa in the tunica albuminear we've seen that the testis themselves are divided into about 250 different lobules and these little tubules are known as seminiferous tubules within the testis and this is where sperm is produced you'll notice the link between the seminiferous tubule and beyond that's known as a straight tubule that's a very good name because it's very straight and then the middle bit is known as the mediastinum testis so we talked about things entering and leaving the testis this is the point where that happens at the mediastinum testis and then we see these efferent ductules efferent means going off going away and so the efferent ductules are going to feed into the epididymus the epididymus and so the head is at the top over like that and then the tail comes around the back of the testis like that so here's the head here's the tail and you can see this tubule then becomes continuous with the vas deferens which is now going to leave in this very complicated spermatic cord all right so we've got the nerves coming in we've got the artery coming into the testicle we've got the pampiniform plexus and we've got the other veins leaving as well as lymphatics and then the all-important vas deferens there too so I think that's quite an important slide to understand helps to explain the spermatic cord quite nicely as well okay so we've talked about the head of epididymus body of epididymus tail of epididymus and the ductus deferens which is continuous with that tube okay so there are in fact three cell types within the testis so the reason why we're paying a lot of attention to the testis is because this is where sperm is produced so you need to understand where are those sperm cells coming from how are they supported and how do they mature so those little tubules all those wiggly lines deep within the lobules of the testis they've got two cell types they've got the sustentacular cells also called sotoli or nurse cells and these cells are sustaining if you like the sperm the developing sperm so they are the ones that are looking after that's why they're called nurse cells they're looking after the developing sperm so just for the moment we need to just believe that they produce inhibin and androgen binding pro protein i like the name of both of those substances because they'd explain what they do we'll come back to that in a minute the all-important germ cells they are here too all right so we've got the germ cells which are producing sperm cells from puberty the production of sperm will start and so the germ cells are the site of continuous sperm production so unlike what we saw in the female where we get this sort of cyclical development of just one oocyte eventually that gets ovulated in men we have germ cells that are continuously producing new sperm and then there are the interstitial cells the interstitial cells or the laodig cells and you might be confused by the fact i've used the word two here because the interstitial cells are located outside of the seminiferous tubules so i've put them here so that you've got the list of all three but these two are inside the seminiferous tubules these interstitial cells otherwise known as laodig cells they're outside of the seminiferous tubules and they're really important because they're the guys that produce testosterone all right so make sure you understand that it's laodig cells producing testosterone and that's outside of the seminiferous tubule inside the seminiferous tubule it's all about nurturing developing germ cells or developing sperm cells so some hormones that will be familiar to you we've got the interstitial cells or laodig cells producing androgens like testosterone but this is under the influence of luteinizing hormone and if you remember luteinizing hormone comes from the anterior pituitary do you remember that of course you do yep so this is the histology of what we've just talked about so this is the wall of the seminiferous tubule and we've got some cells outside of that wall all right so they must be the laodig cells or interstitial cells and those are the guys are making the testosterone all right so testosterone is produced outside of the seminiferous tubule inside the seminiferous tubule you can see how busy it is but if you look really closely you can see that we've got almost sort of like columns or stripes and then in the lumen in the space of that tubule if you look really closely you can start to see things that look a little bit like sperm shapes all right so look at that one that one looks very sperm shaped and is there another one hmm that was the best one i think that's the best one that one looks sperm shaped as well and then you can see all of these tails in the lumen all right so we've got something going on here in this seminiferous tubule where we've got cells turning into sperm in this point so the laodig cells they're the ones outside of secreting testosterone then we've got the sustentacular cells producing androgen binding protein that's these big guys and they are supporting the developing sperm right so you can call them nurse cells as well and what androgen binding protein does is it gets that testosterone that's produced outside and it holds it it binds it so there's plenty of testosterone in the testes at any one point so it doesn't all float off into the bloodstream so we need testosterone for this process then of course we've got the all-important germ cells and we have the sort of original the sort of um what's it the stem cell if you like the spermatogonia they are the source of the sperm to begin with and those cells need to divide into two one's going to stay like a stem cell the other one is then going to differentiate into a fully mature sperm so that you've got a constant supply of new um new sperm cells so the germ cells start off as spermatogonia and then they will subdivide and i'll show you that in just a minute so spermatogonia if they are going to differentiate into sperm they become spermatids first and then they eventually become sperm that will then head off through this tubule lumen through this straight structure and into the epididymus where they're fully mature so i'll keep going for about another five minutes and then i'll give you a break so we'll just get through this sort of physiology and then we'll we'll stop for a minute so in terms of the hormones you'll have heard of all of these before so in the male uh the hypothalamus is producing gonadotrophin releasing hormone at puberty in those pulses and then we get to follicle stimulating hormone and luteinizing hormone both of those are produced in the anterior pituitary and then these are going to be acting in the male in different ways but when we get to the testes as you know we get the production of testosterone by those ladig or inter interstitial cells so what's going on first of all we get GNRH secreted by the hypothalamus which will stimulate the anterior pituitary to secrete LH and FSH so that's a familiar story isn't it it happens the same in the female but in the male the luteinizing hormone is going to stimulate those interstitial cells or ladig cells and tell them to secrete testosterone that is the message all right so LH is stimulating interstitial cells to secrete testosterone and that gives the male secondary sexual characteristics the libido the sex drive and that maintains that sort of maleness if you like throughout life FSH does something different and again remember follicle stimulating hormone in women that's the one one that's causes those primordial germ cells to mature and eventually create an oocyte that gets ovulated FSH in the male stimulates the sustentacular cells to secrete androgen binding protein which keeps those testosterone levels high in the testes and it's the testosterone in the testes that stimulates spermatogenesis it also when when we got the right amount of that it will have a negative feedback to inhibit GNRH secretion and quieten the anterior pituitary sensitivity to that GNRH so it's the presence of testosterone that gives us that negative feedback on top of that we see that when the sperm count starts to rise the sustentics sorry sustentacular cells will secrete inhibin and inhibin will further inhibit FSH secretion as well so that means that we don't overproduce or underproduce sperm we've got this constant negative feedback and when levels drop that negative feedback is lost and up it goes again negative feedback quietens it down so we see this sort of oscillation of testosterone and inhibin so that's it for the the male in terms of that hormonal control that's what i want you to know if we now go back to the testes and now we're inside that seminiferous tubule you can see we've taken those uh sort of cross-section through this here are the ladyg cells hope you're all saying well those are the ones producing testosterone because they're and now we're going to see sperm production so we start off with that kind of uh like stem cell that first germ cell known as a spermatogonium so the germ cells are the origin of sperm they're diploid so they've got their 23 pairs of chromosomes and they're called spermatogonia spermatogonia so what happens is one spermatogonium divides into two and there'll be one with the star shape here that one is going to be a committed cell and sorry no that one's the committed cell and this one is going to be the new germ cell all right so this one will stay looking like that one and it will be the source of the next generation this one is now going to commit to being a primary spermatocyte and as we know it's still diploid all right so we've got 23 pairs lost my mouse 23 pairs here those are going to replicate 23 pairs here 23 pairs here this one is now going to further divide and that's going to undergo meiosis one and make haploid cells so these are now secondary spermatocytes so instead of 23 pairs there's 23 chromosomes in each all right so those have been separated out and then the haploid secondary spermatocytes will undergo meiosis two resulting in these known as spermatids and these are all haploid cells of 23 chromosomes all right so these are haploid but what they've done because they're going to divide they've copied all their DNA their genetic material and then they've divided into two so you've got four haploid cells now so we've got that one spermatogonia that's then created a committed cell which now has four offspring and at this point we're going to divide we're going to have an x chromosome and a y chromosome all right so the future sex of the baby if one of these sperm were to fertilize the uocyte this is decided at this point all right as to whether this is carries an x chromosome or a y chromosome and then of course there are about 800 million up to 800 million sperm in an ejaculate and only one of those could fertilize an egg so that whatever that sperm was carrying is going to determine the sex of that embryo and then finally we have these spermatids undergoing what's called morphologic changes in shape and that's what they need in order to form mature sperm known as spermatozoans that are fully motile so the ability to swim is critically important so this stage of morphogenesis is called spermiogenesis all right the production of mature sperm so you can see they go from looking like this to looking like this when they're fully mature so spermiogenesis is where we have this nucleus which is the important bit lots of cytoplasm lots of mitochondria but essentially what we're going to end up with is the sort of head of the sperm is going to change shape and the cytoplasm is going to change shape as well and most of it's going to be lost but we're going to get this flagellum a motile flagellum that is going to start to develop all of the mitochondria here as you know they produce energy the mitochondria are going to sit around the head of this tail so they're providing energy for motility for swimming so we can now see that the nucleus is kind of covered with this little swimming hat and then we've got the tail coming off at the back which is providing motile force the mitochondria have now lined up either side at the top of the tail and there the guys are going to give the energy to this flagellum to swim so this is what a mature spermatozoan looks like and the acrosome cap some of you may know that there are some important enzymes in there that enable the sperm to once it's attached to the egg to sort of bury its way through to reach into the cytoplasm of the oocyte and that's known as the acrosomal reaction so that's the mature spermatozoan and all of that is going on in the testes and in the epididymis so if you wanted to know your genetic numbers this slide just shows you how we go from 46 chromosomes or rather 23 pairs to another primary spermatocyte that has 23 pairs then we have 23 chromosomes not pairs so these are haploid 23 single chromosomes here and haploid 23 chromosomes here but these the differences that they're now motile they can swim okay so i'm going to stop there it's nearly 12 o'clock so i'm going to start again at 10 past 12 if you've got any questions do come down to the front and i will put the QR code up again the epididymis is where sperm is produced stored and matured all right so we've got sperm moving across from these seminiferous tubules into the epididymis the main reason why we have the epididymis is for sort of final production storage and maturation of sperm so we can think of it as having a sort of an internal being an internal duct with an external covering of connective tissue and it's remarkable but the duct of the epididymis is four to five meters in length and i've brought a very handy shoelace here which is that's about a meter all right so four to five of those tucked away in each epididymis that's quite impressive isn't it so that's how convoluted that tubule is we've already talked about where the head the body and the tail are and the fact that the epididymis is where the sperm are stored while they mature and when fully mature that means they're their best swimming capability and it takes about two weeks for sperm to sit in the epididymis and really get that swimming ability under wraps so any un-ejaculated sperm those will be reabsorbed by the cells lining the duct so they never leave the testes or i will never leave the epididymis and then the other important thing oh we'll say talk about that later but essentially if a couple are trying to conceive then it's important that the man doesn't ejaculate too frequently because the the number the sperm count will go down because sperm production is fairly consistent so if there's sort of too many ejaculations if you like the sperm count will drop so that's just something to be aware of we can move on to the ductus deferens now that tube its job is to carry ejaculated sperm from the epididymis right the way around to those ejaculatory ducts it's a thick walled tube of about 45 centimeters in length so the ductus deferens is about that long all right so that's not short is it that tube will go from the tail of the epididymis into the spermatic cord through that inguinal canal we talked about and entering the pelvic cavity and there it will pass posteriorly along the urinary bladder and then it will it will basically pass inferiorly and enlarged to form the ampulla so there's widened bits of the ductus on the back of the bladder and from that point they will join with the seminal vesicle and form an ejaculatory duct okay so the ductus deferens is that long tube that essentially links the testes with the ejaculatory duct yeah we've seen where it terminates close to the region where the bladder and the prostate meet so i think yeah i did put the diagram in so here's our ductus deferens up it goes and then remember this is a posterior view so it goes in front of the ureter and then it widens to this ampulla down it comes and it joins the seminal vesicle to make these two ejaculatory ducts which then feed into the urethra all right so this is where sperm will move through on ejaculation so we can now talk about the seminal vesicles these are these giant structures that sit immediately inferior to the ampulla of the ductus deferens and the seminal vesicles job is to secrete a thick white yellow alkaline fluid to add to the sperm so what's coming through the ductus deferens is predominantly sperm and then we need this seminal fluid which contains fructose and prostaglandins to really give the sperm sort of energy in order to increase their motility so this is the viscous whitest yellow fluid and this is alkaline and so they're paired we've got left and right and they are on the posterior surface of the urinary bladder and they are lateral to the ampulla of the ductus deferens they're about five to eight centimeters long so they're surprisingly big and they're hollow so they've got this hollow tube in the middle which is where that fluid will pass down and so it will mix with the sperm in the ejaculatory duct and then end up in this prostatic urethra here so the ejaculatory ducts are merely like little drain pipes if you like they're just conducting the sperm and the seminal fluid together into the prostatic urethra so they're only one to two centimeters long they're quite short but it's really important that this gets funneled to the right place to this prostatic urethra so we can move on to the prostate gland you'll have heard of the prostate gland because men often get a bit of trouble with their prostate gland as they get older they might get benign prostate hypertrophy where it just gets bigger or of course there is prostate cancer which can be quite problematic for many men as they get older in particular so the prostate gland as we can see is sitting right immediately inferior to the bladder it has the urethra the prostatic urethra passing through it and now we know it has these two ejaculatory ducts that feed into it as well so its job is to secrete a complex milky fluid which is added to the sperm as they pass out of the ejaculatory duct so it's the sperm and seminal fluid really as they pass out to the ejaculatory ducts the gland itself is around about 20 grams it's compact it's quite dense and it's got a capsule around it so its sort of size is sort of maintained it's about the size of a walnut two by three by four and the main two glandular tissues which will open directly into the prostatic urethra we have submucosal glands from the prostate and tubular alveolar glands from the prostate so the submucosal glands are producing mucin so that's like a sort of watery mucus layer to aid with lubrication the tubular alveolar glands are producing important substances from the prostate so the important substances are citric acid seminal plasmin and prostate specific antigen we sometimes use this as a test to see if the it's overgrown so citric acid is like a nutrient for sperm helps get more life and motility seminal plasmin is antimicrobial so that helps to prevent infection and prostate specific antigen is an important enzyme and its job is to liquefy semen at ejaculation so it becomes much much thinner than it was just with the seminal fluid all right so it liquefies it so it makes the semen more motile when it's in more of a liquid environment so the pH of prostate secretions is slightly acidic due to the presence of the citric acid but the semen itself remains alkaline and it needs to remain alkaline because of the fairly hostile environment of the more acidic vaginal environment all right so again protects the sperm we mustn't forget the little bulbo urethral glands those are sitting in the pelvic floor and their job is to produce a clear mucus for lubrication specifically of the urethra so that when these fluids are passing through the urethral wall the lining of the urethra doesn't get damaged so these bulbo urethral glands produce that mucus for lubrication of the urethra during sex and they're sort of p shaped and sized and they sit within those pelvic floor muscles those are known as bulbo urethral glands so their secretion is clear and it's fairly thick mucin to create this kind of mucus coat and lubricate the urethra for eventually the passage of sperm and in older textbooks they're urethral glands now that's quite helpful because they're shaped a bit like a light bulb and they are there to lubricate the urethra so that's a kinder label I guess.

And then finally the semen and ejaculate we've had all of these different secretions added to it so semen is the term we use for this combination of seminal fluid and the sperm combined so it's all of these different additions that make the mature semen 10% of semen is sperm 60% is seminal fluid which came from the seminal vesicles 30% is prostatic fluid and then we've got some urethral mucus from those bulbo urethral glands so semen should be cloudy sort of milk white in color and if ph testing it slightly alkaline and the word ejaculate is the sort of clinical term for semen released during sex or orgasm and on average for men it's about three to five mils per ejaculation and then this figure is truly staggering there's between 80 million and 500 million sperm per ejaculation that's a normal sperm count all right 80 million to 500 million per ejaculate and for the average sexually active male it takes about two weeks from production to ejaculation and something I mentioned earlier that highly sexually active men may have a lower sperm count due to a dilution effect and that's because the volume of the ejaculate remains fairly constant but and the sperm production rate remains fairly constant and so that means that the sperm count will come down so I thought it'd be nice to stop talking for one minute and 40 seconds and we'll watch a little video to remind ourselves of the anatomy let's hope it works whoops don't know if that's going to work no that's not one either sorry folks let's just uh I think I clicked something okay we'll have to have it in silence it's just labeling all the structures showing you in 3D these are all the structures that we've seen it's really complicated tubular network isn't it so this is showing the passage of urine from the bladder and then it's showing you an erect penis and it'll show you the passage of semen and sperm so there it goes through the vas deferens joined with fluid from the seminal vesicle together they go through the ejaculatory duct into the prostate which will add some more fluid and then hopefully yep so it sits as a bolus there and then it's ejaculated out through the urethra so I think that's it so I've put that up for you so that you can watch that again as a separate thing on blackboard so hopefully you'll be able to hear it as well don't know why the sound didn't work but I think that's actually a very good little video because many men and women don't fully understand the anatomy of the male reproductive system and all the tubular networks and how it all works so if somebody was to get erectile dysfunction or a problem with their prostate many people don't know what their prostate does or how an erection comes about all of those things so starting off with a little video like that for patients is actually quite a helpful thing to do so what we're going to do now is move on to the anatomy of the penis and then here we've got the anatomy where we want to remind ourselves that we've got the urethra that's passing through the pelvic floor that will go through the shaft and the body of the penis and it will come out it should come out right at the tip of the glands known as the external urethral orifice we now need to recognize that the structure of the penis revolves three erectile bodies so we have these two paired columns here and then we have this central more ventral column here all right so this is called the bulb of the penis where we've got this central column here where essentially this structure known as the corpus spongiosum will expand at the end and that's continuous with the glands so it starts off within the pelvic cavity that's where it's kind of anchored and then it goes outside and then ends at the glands penis and then either side we've got these other two columns of erectile tissue so that was the corpus spongiosum sorry then we've got these other two columns of tissue and these are in sort of attached if you like to the pelvic bone on the inside they follow the pelvic bone on either side this is called the crust or cross of the penis and then that makes the pain oil shaft on the top and these are called the corpus cavernosa so you've got one on the left and one on the right so that makes up the three erectile bodies of the penis and when it's in its flaccid state these are sort of sort of spongy muscular tissue so the penis and the scrotum are the external genitalia in the male as we've seen and the root of the penis is attached via what we've seen as the bulb and the crust so the bulb is attaching the bulbospongiosis muscle found in the urogenital triangle so that attaches that part of the penis to this muscle and the crust on either side attaches the penis to the pubic arch so alongside those two pubic bones the body of the penis is also known as the shaft and that's the sort of elongated movable part and the glands penis is the extended tip with the external urethral orifice right at the end and that's continuous with that other erectile body known as the corpus spongiosum so there's one corpus spongiosum which is ventral and then we've got the two corpus cavernosa on either side left and right in terms of blood supply it's the internal pudendal artery which is giving the main blood supply to the penis and that's a branch of the internal iliac artery so that internal pudendal artery will branch become in the common penile artery distally and that then branches three times into a dorsal artery a bulbo urethral artery which supplies the corpus spongiosum and the cavernous arteries which will supply both corpus cavernosa and then the arteries within there known as helicon arteries venous drainage is of the penis is via the internal pudendal veins and the dorsal veins of the penis so if we have a little look at a transverse section through that you can see this is the corpus spongiosum which is ventral and then we've got the corpus cavernosa on the right and on the left and you can see these are these are kind of cavities as well as being sort of structures they've got cavities so they've got the capacity to sort of fill with blood or engorge with blood so within the penile shaft we've learned there are three cylindrical erectile bodies the two corpora cavernosa or a singular corpus cavernosum that are located dorsolaterally and these will end at the end of the shaft and then we've got one corpus spongiosum in the midline which is ventral and that contains the spongy urethra so this structure here is actually the urethra where urine and sperm pass through and this will end at an expansion called the glans penis which is this area here so we can think of the three erectile bodies essentially as cylindrical chambers and they're made up of sinusoids which are like little rivers of capillaries and smooth muscle networks so there's smooth muscle in here as well and there are veins that are helping to drain those important sinusoids so we've got those three erectile bodies making up the cylindrical chambers so again that's just showing it in more detail the corpus cavernosa on the left and the right and then the corpus spongiosum which is that more ventral structure with the urethra in the middle and you can see that there's an artery coming in to supply all of these three structures and importantly it's got within the corpora cavernosa we've got these venous spaces and we've got an artery running through the middle the spongiosum has also got these venous spaces but instead of having an artery running through the middle it's got the urethra this is called a tunica albuginea not to be muddled up with the tunica albuginea of the testes this is like a covering that provides sort of support and also confines the shaft of the penis so that's continuous ring that goes around these structures and that's really important for maintaining an erection all right because that is confining the blood that's going to fill these these cylindrical chambers and then this is supported by deep and superficial fascia as well so this is not stretchy all right so these are able to confine these tissues and then right at the very end the clinical term for a foreskin is the prepus and that's the skin covering the entire penis sorry that's the skin at the distal end that's attached to the raised edge of the glans penis causing it to form a prepus or a foreskin and this can be removed surgically often in infancy and is known as a circumcision so we're now going to move on to the physiology of the male reproductive system so of course the male reproductive system is to produce the male hormones specifically testosterone and to give male secondary sexual characteristics another function of the male reproductive system is to produce mature and to store fully developed sperm and for that we need testosterone and then finally the physiology of the male reproductive system is all about that transference of mature sperm in a biological sense into the female reproductive tract that's known as ejaculation for fertilization and the production of a genetically unique new human life and for this to happen an erection is essential so the clinical term for erection is either erection or tumescence you may see that word used and for that it requires intact neuronal connections and control over the blood supply and that's what we're going to talk about now so the male sexual response has four stages to it the first one is arousal and excitement in order for the male to get an erection and for that we need the parasympathetic nervous system we'll talk about that in just a minute so it's the parasympathetic nervous system that brings about erection for emission and expulsion i.e ejaculation that requires the sympathetic and to a lesser extent the somatic nervous system so this is really unusual in sort of human biology where you've got the autonomic nervous system working almost at the same time parasympathetic and sympathetic parasympathetic to bring about erection sympathetic to bring about ejaculation then after that is the process of resolution where the penis has got to return back to its flaccid state and then there's a refractive period which is an inability for a man to attain another erection for a certain period of time so in order to remember it's a classic point is parasympathetic so that's an erection and then shoot is sympathetic so the s marries up with sympathetic that way you won't get those muddled up so point is for erection shoot is for ejaculation so let's have a look at the physiology then of an erection so it occurs due to simultaneously what how does an erection even happen biologically it's due to the fact that the arteries supplying the penis will dilate and that means that blood will rush into the penis and then venous occlusion the outflow the blood going out those veins will start to shut down and therefore you've got a good inflow but no outflow and so that means that therefore the blood is going to engorge the tissues of the penis so blood is entering those three erectile bodies and it can't flow out and the blood flow is increased up to 20 or 40 times the normal amount and so it will fill all the sinusoids all of those little rivers of blood within the penis all of those erectile bodies will fill with blood so they will therefore expand and harden the erection is maintained because that blood can't escape at this stage so it can't flow out so that's how the penis remains erect and as we've learned that requires parasympathetic activation it's the parasympathetic nerves that open up the arteries and then muscular contraction back at the root of the penis is going to strengthen that erection so in terms of arousal and excitement we've learned it's the parasympathetic nerves via pelvic splanknic nerves sacred nerves s2 and s3 causing the erectile bodies of the penis to engorge with blood and what are the parasympathetic nerves doing ultimately nerve signaling triggers nitric oxide release in response to arousal and you may or may not know that nitric oxide is a potent vasodilator so it causes smooth muscle relaxation so it's this nitric oxide that acts on the penile artery smooth muscle and causes it to dilate nitric oxide will also activate GTP to CGMP and there's some notes on my slides just to explain what those are if you don't know and again that will relax the smooth muscle within the erectile bodies so we've got lots of relaxation going on which is what the parasympathetic nervous system is all about and that means that blood can flow in to the three erectile bodies as they fill up they compress the veins that usually drain blood away from the penis therefore the spaces in the penis will fill with blood and that blood cannot leave and that results in an erection so then we get to the ejaculation stage this stage is not the parasympathetic nervous system it's now the sympathetic nervous system and these come from what we call lumbar splanknic nerves ultimately it leads to the ejaculation of the semen that we've talked about through the glands and that comes via rhythmic contraction of smooth muscles in the walls of both the ductus deferens and the urethra to a lesser extent the prostate itself as well so we've got contraction of the ductus deferens and we've got contraction in the urethra and some contraction here at the prostate so the ductus deferens undergoes peristalsis smooth muscle contraction to move the sperm up and around through that duct all the accessory glands that we've talked about they're going to release their secretions into the tubular system therefore mixing the sperm with liquids to form semen as we talked about earlier the internal urethra so where the urethra and the bladder meet that will close so urine cannot be expelled during ejaculation and then constriction of the urethra all the way along here helps to sort of narrow that tube if you like and that then causes propulsion of the ejaculate rather than it coming out slowly it comes out quickly so that's known that first phase is known as emission and emission requires as we've seen sympathetic nerve activation so the sympathetic nervous system is stimulating smooth muscles in the epididymis the vas deferens the seminal vesicles and the prostate glands so there's neuronal control over all of this the smooth muscles will then contract moving the sperm from the epididymis and the seminal fluids from the seminal vesicles and the prostate into the urethra and at this point the semen and all of those secretions is going to collect in the prostate in the urethra of the prostate in preparation for expulsion all right so it's going to just sit there just for a minute and then the distension of the prostatic urethra by the presence of this kind of bolus of seminal fluid and sperm stimulates an important reflex arc and that leads to expulsion so the pudendal nerve that reflex arc involves a pudendal nerve which is part of the somatic nervous system rather than autonomic so this pudendal nerve it's signaling muscular contraction of both bulbospongiosis and ischocabinosis muscles of the pelvic floor which undergo rhythmic involuntary contraction and then these contractions will forcibly eject semen along the urethra and out of the body and that goes via that urethra and out via the glands all right so expulsion is where we get this kind of reflex arc muscular contraction of all the muscles in the pelvic floor and around the pelvic floor and that's then going to push the semen out of the urethra so with that we call that sort of orgasm and that culminates in intense feelings of pleasure release of tension and forcible expulsion of semen and then after that phase we get to what's called post-ejaculation resolution and refraction so the resolution phase is where the sympathetic nerves here cause that central artery to contract so sympathetic nerves cause central artery to contract and as well as the smooth muscles around the penis so this is a way of sort of squeezing out if you like the engorged blood that was within those erectile bodies.

Rejection in autonomic activity as a whole after ejaculation reduces the blood flow to the penis so that shunts most of the blood away from that area and that means the penis should return to its flaccid state so it's no longer erect and then a man will have what's called a refractory period so that's where another erection can't be attained during that stage and for some men it's minutes and for other men it can be hours and it's known that the duration of this refractory period lengthens as men get older.

Okay so let's say the sperm has ended up in the female reproductive tract and this is our last slide set all right so sperm are going to travel through the female reproductive tract and it should arrive high in the vagina and go throughout the uterus and eventually swim into the uterine tubes both on the left and the right and we know that sperm will remain viable it'll stay alive in the female reproductive tract for up to three to five days all right so viable means these sperm are actually able to penetrate the ovum only one of those sperm as you know is able to fertilize an ovum and that's provided ovulation has occurred within 24 hours so sperm can kind of hang around for a while but it's got to coincide with the presence of an oocyte that's younger than 24 hours since it's been ovulated because an ovum cannot be fertilized more than 24 hours after ovulation so I thought it'd be good to watch a little experiment of how sperm once it's kind of swum through the female reproductive tract what sperm does when it's approaching an an oocyte or an egg and this is a really short video that hopefully it can show you how how it changes so luckily there's um it's we've got a professor of food science used chambers to observe to shift in sperm behavior known as hyperactivation so sperm normally swimming nice and straight that's to get them into the female reproductive tract then they've added a load of calcium and sperm start swimming round and rounded circles and it's thought that this emulates what happens when they get close to an egg instead of swimming straight past they kind of circle and then they can get to the oocyte so the idea is is that that will help with in vitro fertilization that's it very quick video but it's always nice to have a little video I think at the end okay let's go back to here so it's a bit of an abrupt ending but um we're out of time and we've covered everything that I wanted to cover lots and lots of information I hope you found it interesting I think your attention has been amazing and I didn't go red once which I normally do but I've managed not to go red so hopefully you're a bit more familiar now with the AMP of external internal genitalia in the male and then go through those slides a bit more slowly than I did to go through the physiology of erection and ejaculation and then puberty is quite well covered in Ross and Wilson so do have a look at that and I'll see you all for your um seminar workshops thank you for your attention