ASRM CELL Module 1: Introduction to Male Reproductive Physiology and Endocrinology

Lecture 1 - Male Reproductive Anatomy and Physiology (PDF) →

Lecture 2 - Hormonal Control of Male Reproduction: Regulation and Clinical Implications (PDF) →

Ah, there we go. Perfect. Very good.

So, we're still three minutes, so we'll wait for other participants, but welcome everybody who's here so far. Thank you. Hi, Leandro.

Welcome. Hello. How are you doing today? Good.

How about you? Doing good. Thank you. So, we'll just wait a couple of minutes, a couple of more minutes for Andrea.

Oh, here she is. And then we'll go ahead and get started. Hi, Andrea.

Can you hear us and see us? Yep, all set. Okay, good. Welcome, guys.

Good evening to good afternoon, depending on where we are. And I would like to do a very, very short introduction in the interest of time, and then we'll go ahead and get started. Just a general housekeeping statement that you have two lectures today, each is about one hour.

I did send some preliminary, some questions that I hoped you will look over and do a little pre-test in the privacy of your own office. So, there is no reason to look up the answers. This is just for you to check your baseline, and then later we will introduce more formal approach, but so to just ease you in into this process.

And then I recommend that you retake the test within 24 hours after your lecture is done, and then just report to us if you improved or, you know, any other comments on that. So, I will introduce our faculty very quickly. So, I am Marina, your Cell Program Director, and our first lecture will be by Kausi Selakanu, Dr. Selakanu.

Kausi has her doctoral degree in human anatomy, so it's a very, very fitting subject for her background, but she's also an ELD and embryologist with a very, you know, long and good experience. And, yeah, I already said she's an ELD. And the second lecture will be by Yining Li.

She is a PhD, HCLD, and her PhD is in reproductive biology, so also very apropos to our today's theme. And now I want to, our scholars, to introduce yourselves, like very, very briefly, basically of, you know, your highest educational degree and your years in the embryology lab, and very briefly your skill set, so the faculty will know how to moderate their material based on the audience. So, I'll start with you, Leandro.

You are first on the screen. I'm not singling you out. All right.

So, my name is Leandro. So, I'm an embryologist with a post degree in biotechnology. I'm in the embryology field for about 13 years.

10 years of those are in the animal field, and then I did my transition to the human side. And I'm located in Florida with IVFMD. Sounds great.

And then who is next? Andrea? Hi, yes. I have my bachelor's in microbiology, and then I started working in the embryology lab right out of college, and I've been there for three and a half, almost four years now. Okay.

And then Joseph, you do go by Joseph or? Yeah, Joseph is fine. Okay, good. So, I have a medical degree and then did residency in obstetrics and gynecology, and now practicing in a REI practice, relatively new to the laboratory side, but a little bit stronger background in the clinical side of this process.

Okay. Sounds good. And so, your goal is to become hands-on, fully trained embryologists? That's my goal.

And to include an HCLD at some point, right? Yeah. The goal is to get the technical skills to make the transition at some point to HCLD. Sounds very good.

And I see that Stephanie, my partner in crime and developing cell program, just joined. Thank you, Marina. So, I just introduced Kausi and Yining, and I don't know if you met them in person, but you for sure know about them? Oh, for sure.

Yes. Okay. So, we'll just go ahead and get started now.

We just did the introductions, and Stephanie is at Yale University. She's a scientific director there, and she's fabulous. Marina, thank you very much, as are you, of course.

You guys, we're very excited for everybody. I can't wait to kind of get started. I will say that I also reviewed the questions that Marina sent out, and I thought, ooh, I need a review as well.

I know. Don't we all? I mean, it helps. Why not? And it's fun.

Excited for tonight. I mean, studying is forever, as far as I'm concerned. Yes, it never ends.

It never ends. So, I'm going to mute myself now. And myself, yes.

Don't let me unmute myself. And happy work. All right.

Can everybody see my screen? Yes. Okay. Perfect.

Thank you. Thank you for that introduction, Marina. I'm going to quickly start with our first lecture of this inaugural series of this initiative by ASRM.

So, for want of time, let's get quickly started. All right. So, over the next few weeks, as Marina mentioned, you're going to listen to a lot of experts from the IVF field and embryology, and these lectures are designed to make us think beyond what we do in the embryology lab, what we do at the bench, kind of give us an understanding of what happens in the background, more understanding about the male and the female infertility.

So, we're starting off the series with the male reproductive system, and this is a two-part lecture. So, the first hour, I will be focusing on the anatomy of the male reproductive system, understanding spermatogenesis a little bit more, and part two of this lecture will be given by my good friend and colleague, Yining, and she will focus more on how the male reproductive system is regulated, particularly the hormonal control. Okay.

So, the learning objectives for this first hour of the session is by the end of the first hour, I would like you guys to be able to understand the origins and the development of the male reproductive tract, identify parts of the male reproductive tract, and understand the microanatomy of the testis, what exactly happens inside the testis, and the function of the blood testis barrier, and understand the process of spermatogenesis, and discuss the semen composition, and finally, the clinical implications of all of this and its applications in reproductive medicine. So, let's get started with the embryological development. This is probably not new to you, Joseph, but to give a brief overview to the other students as well.

So, up until the sixth week of gestation, the development of the embryo is a common pathway, regardless of whether the embryo is an XX embryo or a XY embryo, and from sixth week onwards is when the differentiation starts to happen, whether it's a male or a female. So, in the beginning, there is a structure called the bi-potential gonad, as you can see here. So, this bi-potential gonad eventually forms in the male, the testis, and in the female, the ovary, and along with the bi-potential gonad, you have the two ductal systems.

The one in red is the mesonephric duct that's right next to the bi-potential gonad, and this mesonephric duct is also called the wolfian duct, and right next to the wolfian duct in blue is the paramesonephric duct, para meaning lying next to. So, the paramesonephric duct lies next to the mesonephric duct, and it's also called the malaria duct. So, I'm going to keep repeating mesonephric and wolfian and paramesonephric and the malaria again and again, so it kind of ingrains into our brain that the mesonephric duct, also called the wolfian duct, gives rise to the male reproductive system, and the paramesonephric duct, or the malaria duct, gives rise to the female reproductive system, which we will learn about in the next lecture.

And then you also have an endodermal primordial derivative called the urogenital sinus, that's in yellow over there, and that will give rise to the rest of the parts of the reproductive system, namely the prostate gland, the prostatic part of the urethra, the bulbo-urethral glands, and also gives rise to part of the urinary system, the bladder. So, now let's take it back a little bit more further. So, before six weeks, let's say about two to three weeks of intrauterine gestation, the embryo is in, is my cursor, are you able to see my cursor? Yes? Okay.

So, at two weeks, around two weeks of gestation, so you have the embryo, you have the head pole and the end tail pole, also called the caudal pole, and then you have two primary structures called the yolk sac and amniotic sac. Now, around the second or the third week of gestation, there are some specialized cells that are developing along the walls of the yolk sac. So, right here, close to the caudal end of the embryo, close to the allantois, you have these specialized germ cells called the primordial germ cells that are forming.

And these primordial germ cells in the future are the spermatogonia in case of male and the oogonia in case of the female. Now, these primordial germ cells are being formed in the walls of the yolk sac, but they need to migrate into the body cavity of the embryo to reach their final destination, namely the gonads. Okay, so eventually, so they start migrating into the body cavity along the walls of the embryo.

So, they split into two populations behind the hindgut. So, hindgut is something that will give rise to the intestines in the future. So, they split into two populations, one to the right side and one to the left side, and they go behind the hindgut along the mesentery and then reach their final destination called the genital ridge.

So, you're able to see here in this view, the cursor that I'm pointing out, that's the genital ridge. And you see that this is the final destination for the primordial germ cells. Now, once the primordial germ cells reach their final position near the specialized structure, that's the genital ridge, eventually, based on whether the embryo is XY embryo or the XX embryo, that's when the differentiation starts to happen.

Now, if it's an XY embryo, there is a region on the Y chromosome called the SRY gene, SRY standing for the sex determining region of the Y chromosome. So, the presence of the SRY gene now pushes this bi-potential gonad into forming the testis in case of the male. And the absence of the SRY gene in case of an XX embryo pushes the gonad towards forming the ovary or the female gonad in case of the female.

So, now that for our purposes, let's assume this is our XY embryo and because we have the SRY gene, now this primitive gonad starts forming into the testis. So, the epithelium that's surrounding this genital ridge starts to thicken. So, you can see this brown thickening.

So, it starts to thicken and it protrudes into the substance of this primordial gonad or the primitive gonad and it starts to form primitive sex cords. As you can see here, it starts protruding into the cortex of the gonad and it forms the primitive sex cords. Now, these primitive sex cords eventually form the testicular cords and then in the future, they canalize to form the seminiferous tubules.

So, as you can see here in this diagram here, they start forming elongated testicular cords and these testicular cords eventually canalize to form our future seminiferous tubules with the primordial germ cells lining the seminiferous tubules and eventually forming the spermatogonia. Now, along when this is happening, the mesenchyme or the surrounding matrix of this primitive gonad, it has these mesenchymal matrix which will give rise to the future sertoli cells and the larynx cells. Now, the SRY gene also helps in the differentiation of the sertoli cells and the sertoli cells has two functions.

One, it helps in the differentiation of another set of specialized cells called the larynx cells which in turn produce the fetal testosterone and the other function of the sertoli cells is itself to secrete something called the anti-mullerian hormone because you don't want the mullerian ducts to be differentiating in a male embryo because the mullerian duct, as I mentioned earlier, also called the paramycinephric duct, gives rise to the female internal reproductive tract whereas the mesonephric duct or the wolfian duct is what we need in terms of the male reproductive system. So just to give a brief summary again of what I just said in the past few minutes, so the genital ridge is a specialized structure that's forming in the intermediate mesoderm of an early embryo and it gives rise to the somatic testicular cells, somatic meaning it's the non-germ cells meaning the sertoli cells and the larynx cells. The primordial germ cells are not formed inside the gonad but they are formed in the yolk sac and then they migrate to the gonad, so migrate from the yolk sac to the genital ridge and then as I mentioned the presence of the SRY gene helps in the sertoli cell differentiation and then the sertoli cells in turn helps in the orchestration of the entire testicular formation.

And the larynx cells, they arise from the mesenchymal cells surrounding this primitive testicular cords that I mentioned and eventually they help in secretion of the fetal testosterone and this testosterone is very important in the further development and the differentiation of the internal reproductive system of the male. Then as I mentioned the testicular cords or the 71st cords give rise to the 71st tubules in the future embryo or postnatally. So now that we know how the testis is formed we are now moving into how the internal reproductive ducts are formed.

So as I mentioned in the undifferentiated stage you have two ductal systems, the mesonephric duct or the Wolffian duct and the paramesonephric duct or the Mullerian duct and for the male we need the mesonephric duct or the Wolffian duct to develop and for this development you need testosterone and where this testosterone comes from? It comes from this newly formed larynx cells in your primitive gonad. In case of females the paramesonephric duct regresses or the Mullerian duct regresses, I'm sorry in case of the females the Mullerian duct is formed and in the males you don't want the Mullerian duct so that Mullerian duct regression is caused by the anti-Mullerian hormone that's secreted again by our newly formed sertoli cells. So this is another diagram where it shows the simultaneous development of the gonad and the internal reproductive duct system.

So as you can see here this is the developing testis, it has the testicular cords which are canalizing to form the semeniferous tubules and the semeniferous tubules in turn make a connection with the primitive mesonephric duct which is the Wolffian duct as I mentioned and then eventually this Wolffian duct forms the male reproductive tract starting from the epididymis, the vas deferens and the seminal vesicle which eventually forms a combined duct called the ejaculatory duct. Now as you can see here initially the gonad is inside the body cavity of the developing embryo and in case of females the ovary is inside the body but the testis is outside the body. So eventually when the testis is formed it needs to descend, it needs to descend down and come to its final location which is inside the scrotum that's outside of the body cavity and why this is important we will learn about this in the next few slides.

But just remember unlike the ovary the testis needs to descend and come outside of the body cavity for spermatogenesis to happen. So again a quick recap of what we just talked about. So the mesonephric duct or the Wolffian duct gives rise to the epididymis, vas deferens, seminal vesicles and the ejaculatory duct and the development of the internal reproductive ducts in the male requires testosterone and testosterone is secreted by the lytic cells and then the paramesonephric or the Mullerian duct needs to regress and this is done by the anti-Mullerian hormone which is again secreted by the sertoli cells.

So now we've discussed the gonad formation and the ducts formation now we need to know how the external genitalia is formed. So again for the external genitalia I'm going to be very brief it has a lot of technical terms you need to remember three important structures. So the genital tubercle and then you have the urogenital fold which is medial to the midline and then just lateral to it you have the labioscrotal swelling.

So you need to remember these three structures. In case of male the genital tubercle elongates to form the body shaft of the penis and also the glans penis. The urogenital fold gives rise to the penile part of the urethra so it kind of folds upon itself and it closes to form a canalized opening which forms the urethra and then you have the labioscrotal swelling on either sides of the urogenital fold which enlarge come together in the midline and they fuse to form the scrotum.

So these are the three important structures you need to remember and the female counterparts in case of the urogenital tubercle it forms the clitoris and then you have the labia minora and you have the labia majora. So the recap again recap is very important. So genital tubercle gives rise to the penis, urogenital folds gives rise to the urethra so as you can see here it kind of folds upon itself and eventually forms a canalized tubular structure which is the urethra which is present inside the penis it's called the penile part of the urethra and the labioscrotal swellings gives rise to the test the scrotum.

Now unlike the internal reproductive duct system of the male the external genitalia is hugely dependent on dihydrotestosterone and not the testosterone. So the internal reproductive ducts like the epididymis and the vas deferens they need testosterone secreted by the lady excels for their development and differentiation versus the external genitalia is highly dependent on dihydrotestosterone which is also a form of androgen but it's more potent and more stronger than testosterone. It is the derivative of testosterone.

Testosterone gets converted to a dihydrotestosterone by the enzyme 5 alpha reductase so this is the very important difference you should remember between the internal reproductive system and the external which we will read further about in the disorders of sex development in the lectures. So as I mentioned the clinical relevance of the development of the male reproductive system anything that can happen from what we mentioned either the problem with gonadal development or internal reproductive ducts or the external reproductive they all come under the category of disorders of sex development and they fall in the spectrum of infertility they can lead to infertility. It could be a gonadal dysgenesis or it could be a malformed duct system or it could be an ambiguous genitalia they all fall under the spectrum of infertility.

Infertility can be a symptom of disorders of sex development so it's important to have a brief understanding of how the male reproductive system is developed. Now that we have seen the embryology of the system we are moving on to the actual anatomy proper so an overview of the male reproductive system so we can divide it into two external reproductive structures that's outside the body cavity and then the internal reproductive structures. So the external reproductive structures as you can see in this picture here so you have the penis and then you have this crotum.

The internal reproductive structures can be divided into the gonad as such which is the testis and then the ductal system. So the ductal system begins with the epididymis right next to the testis and then you have the vas deferens and then you have the seminal vesicle which is actually the accessory sex gland. So the vas deferens continues as the ejaculatory duct which you cannot see this in this picture so basically what happens is the vas deferens combines with the duct of the seminal vesicle to form a combined duct called the ejaculatory duct which opens into the urethra over here.

Now urethra itself is a long tubular structure which has three parts to it as you can see this part is enclosed by the prostate gland which is called the prosthetic part of the urethra. Then you have part of the urethra that traverses the urogenital diaphragm and that's called the membranous part of the urethra and then you have the part of the urethra that is traversing the penis which is also called the penile part of the urethra. So the duct system as I mentioned starts with the epididymis vas deferens combines with the duct of the seminal gland to form the ejaculatory duct that opens into the prosthetic part of the urethra.

Next comes the accessory sex glands so the accessory sex glands one you have the seminal vesicle the seminal vesicles are paired structures they are on the right and the left hand side so the right seminal vesicle combines with the right vas deferens to form the right ejaculatory duct and then the left similarly the left ejaculatory duct. The next accessory sex gland is the prostate gland. Prostate gland is a single midline structure it surrounds the prosthetic part of the urethra and next you have tiny bulbourethral glands which are important for mucus secretion they're also called Cowper's gland and they are present right next to the urogenital diaphragm which you cannot see in this picture but I will show it to you in the following pictures.

So this is an overview of the parts of the male reproductive tract or the system. Let's go into a little bit detail about each part of the male reproductive system starting off with the external genitalia so the first organ we are discussing is the penis there's a function of the penis it acts as an organ of copulation so it helps to deposit that semen that's produced within the male reproductive system and deposits into the vaginal tract of the female reproductive system and it not only acts as a conduit for semen it also it's a common conduit for semen and urine so it's also part of the urinary system. So when if we are to describe the structure of the penis anatomically we divide it into three parts called the crust the body and the glans penis so if you can see in this picture here so this picture here if you were to straighten out the penis and view the penis from underneath which is the ventral aspect of the penis starting from the base you have the two crusts or the crura and the main function of the crura of the penis is to anchor it to the pelvic bone and provides support and stability to the penis especially during erection.

Next coming to the body of the penis the body of the penis is also called the shaft of the penis and the cross-sectional view of the body of the penis you have three specialized erectile tissue as you can see here the corpora cavernosa which is a paired structure it's on the dorsal aspect and then you have a single corpus spongiosum that's on the ventral aspect so the corpora cavernosa it's a vascular space it has a lot of empty space it can get filled with blood so erection is a vascular event so it's able to fill rapidly with blood and this and prevents the blood from escaping out and helps to form the rigidity of the penis during erection. The corpus spongiosum is another erectile tissue it's in the ventral aspect it's a single midline structure and it encloses the penile part of the urethra so as you can see here this opening in here is the penile part of the urethra unlike the corpora cavernosa the corpus spongiosum does it does get filled with blood but not to the extent of corpora cavernosa because it needs to keep the urethra patent it needs to keep the urethra open for during the process of ejaculation for the semen to go out okay so that's the body of the penis main thing you have to remember is the erectile tissue the corpora cavernosa which is responsible for erection it's a vascular event gets filled with blood and the to keep the urethra patent. The last structure of the penis is the glans penis so the glans penis is actually a continuation of the corpus spongiosum and it's a highly innervated structure its main function is it plays an important role in sexual arousal it's highly sensitive and it also has the the external opening of the urethral meatus through which semen or urine is delivered out.

Next moving on to the next external genitalia structure is the scrotum so the scrotum as you can see here in this picture it's it lies beneath the penis it's a pouch of skin and muscle and it helps to house the testis and the scrotum itself is divided into two compartments the right and the left by an internal connective tissue the septum of the scrotum and it's visible externally called this it's called a scrotal raphe so it's the fusion of the right side and and the left labial scrotal swellings embryologically as I mentioned before and it fuses to form the scrotal raphe so the left compartment holds the left testis the right compartment holds the right testis. The main function of the scrotum is not only to house the testis but to maintain a certain temperature for the testis. For the spermatogenesis to happen inside the testis it needs to be at a lower temperature than the body temperature so it's around two to three degrees celsius below the body temperature and how the scrotum maintains this ambient temperature for spermatogenesis there's several mechanisms so the to understand the mechanisms let's understand the layers of the scrotum first okay so we have externally the skin and very close to the skin you have a subcutaneous muscle called the dartos muscle and after the dartos muscle you have a connective tissue structure it's it's it's called the fascia external and the internal spermatic fascia and then you have another layer of muscle but this time it's it's a skeletal muscle it's called a cremaster muscle so you should remember two muscles one is the subcutaneous smooth muscle that's the dartos muscle right next to the skin and after a layer of fascia or a connective tissue you have the cremastric muscle which is a skeletal muscle okay and then after that you have a rich plexus of blood supply and then you have the testis.

So how the scrotum maintains the temperature at a lower two or three degrees celsius lower than the body temperature one the function of the dartos muscle so the dartos muscle is is very close to the skin and its contraction is what causes the wrinkling of the scrotal the scrotal skin so in terms of extreme cold it wrinkles up the scrotum and it reduces the surface area so it reduces the heat loss keeping the keeping the testis at an ambient temperature and not get too cold vice versa when it's too hot when the temperature is too high the dartos muscle relaxes so there's no wrinkling there's you know increased surface area more heat loss and it keeps the testis cooler so that's one mechanism. The next mechanism is if you if you have observed the scrotum you would know that there is no subcutaneous layer of fat so it's skin it's muscle and then there's connective tissue and then there's the testis so there is no layer of fat and as we all know the layer of fat provides insulation so because there is no layer of fat it helps to dissipate dissipate the heat quicker and keeps the temperature of the testis much cooler. The other mechanism to keep the ambient temperature is the chromastric muscle so the testis and bring it down in response to extreme temperatures or stress so basically it pulls the testis closer to the body and then relaxes back into the scrotum so that's our third mechanism and the fourth mechanism and the most important mechanism is this plexus of blood vessels that's surrounding the testis.

So you have a very good rich supply of blood vessels with the plexus of veins that are surrounding the testis and this helps in the countercurrent exchange of heat so there is a good as long as there is a good flow there is no heat trapped within the testis and this is very important clinically because of varicoceles sometimes there can be an obstruction to the venous drainage and then this will cause engorgement of these plexus around the scrotum around the testis and this condition is called varicoceles from and you will see an enlarged scrotum with like a bag of warmth appearance that's what it's called medically and because of this the heat is not dissipated and the blood is trapped it increases the heat of the testis and which affects the spermatogenesis and why this is important if you come across you know males with azoospermia or you know infertility or subfertility you should ask for history of varicocele or varicocele repair where you know spermatogenesis could have been affected because of you know improper drainage of the venous blood. So now that we have finished discussing the penis and the scrotum let's move on to the ductal system. So the ductal system as I mentioned it has the epididymis, the vas deferens and then the ejaculatory duct opening up into the prosthetic part of the urethra.

So let's begin with the epididymis. So the epididymis is a it's a highly coiled duct and it is present closer to the testis so if you were to view the testis from the front if this is the anterior aspect the epididymis begins from the top of the testis coils around the posterior surface of the testis goes all the way down and then continues into the body cavity as the vas deferens. And if you see the parts of the epididymis you have three parts the head also called the caput, the body of the epididymis also called the corpus and the tail of the epididymis also called the cauda.

So the caput, corpus and the cauda or the head, body and tail of the epididymis. The main function of the epididymis is for it to receive the sperm that's pro-spermatozoa that's produced from the testis and then transmitted to the vas deferens. Apart from receiving the sperm it also plays a major role for maturation and providing the motility to the sperm.

You should remember that the sperm that's produced from the testis although morphologically it looks complete it is not physiologically it's not motile it's immotile sperm it needs a certain maturation for it to happen for it to gain motility and for it to be able to fertilize an egg. And you should remember the maturation that happens in the body of this epididymis is different from capacitation. Capacitation is the final maturation that happens in the tract of the female reproductive system for it to be able to fertilize the egg.

What happens here it's not structural changes to the sperm it's just functional changes you know excess cytoplasmic residual bodies are removed the cholesterol that is present around the sperm that's removed and all this leads to the final maturation in the body of the epididymis and provides that sperm the motility. So that's the major function of the body of the epididymis. The head of the epididymis the only function is for it to receive the sperm from the testis through structures called the efferent ductiles as you can see here in brown.

So these are the efferent ductiles that leave the testis and then go into the head which receives the sperm passes on to the body where you know excess fluid is absorbed concentrates the sperm provides the maturation provides the motility to the sperm and then pushed down into the cauda. Now cauda is the primary source of primary function is storage so the main storage area in the entire duct system is the cauda of the epididymis so that's where the sperm is primarily stored. So these are the functions of the epididymis clinical relevance is microepididymal sperm aspiration and testicular sperm extraction.

If you were to ever witness any of these procedures you should remember at least theoretically speaking that the sperm surgically retreat from a testis is still immortal because as I mentioned the motility and that that gaining that function happens only in the epididymis and even within the epididymis if you were to witness a microepididymal sperm aspiration if they were to aspirate sperm from the head of the epididymis you would probably still see immortal sperm because the maturation and the motility is developed only in the body of the epididymis. So this is something that you should remember and you can correlate with when you come across surgically extracted sperm. Okay moving to the next part which is the vas deferens or the ductus deferens.

The vas deferens is a long tubular structure and its main function is it helps in transporting the sperm from the epididymis throughout the duct system and finally by the process of ejaculation out. You should remember that this transport is not passive it is an active transport. The ductus deferens is the walls of the ductus deferens is made by skeletal muscle and because of sympathetic innervation it causes contraction of these muscles and the peristalsis of this tube helps in movement of the sperm along the tube and that's why it's called an active transport and it's not a passive transport.

Special feature of the vas deferens is if you trace the path of the vas deferens so it starts from the cauda of the epididymis it goes all the way up and then enters the body cavity so it winds around the pubic symphysis which is the pelvic bone enters into the body cavity through the inguinal ring passes through the inguinal canal and at this point it is inside the body it's inside the pelvic cavity of the body. Now it winds around the ureter and then when it comes back here you see this seminal vesicle here it before it joins the duct of the seminal vesicle it kind of out pouches it dilates to form something called the ampulla of the vas deferens so this portion which is dilated it's called the ampulla of the vas deferens. Now this ampulla of the vas deferens functions as the secondary storage site for sperm but the main and the primary storage site is the cauda or the tail of the epididymis but the ampulla of the vas deferens is the secondary storage site for the sperm.

Before it joins with the duct of the seminal vesicle together forming a combined unified duct which is called the ejaculatory duct that you see here and then it opens up into the prosthetic part of the urethra as you can see here. Clinical relevance main important thing is obstruction the obstruction can be congenital it can be induced congenital it's it's the CABVD it's the congenital absence of the bilateral vas deferens and this usually is found in patients with cystic fibrosis so if you have a patient and these patients they have depending on where the obstruction is or what is absent they may have a good volume of semen but they may not be having sperm in the in the semen so the seminal vesicle is still functioning properly but if your vas deferens is obstructed it's not transmitting out the sperm so you may have a good volume of semen but you may not have sperm in it based on the level of obstruction. So as I mentioned if you have a patient with azoospermia but a good you know volume of semen you might want to check his history you know a carrier screening for cystic fibrosis check for absence of vas deferens or it could be induced patient may have had an inflammation or an infection or maybe a surgery that could have caused you know additions or obstructions or it could be vasectomy where you nick the vas deferens and then you ligate the cut ends and you induce azoospermia so you don't want sperm to be coming out in your semen.

So these are the clinical relevance of the ductus deferens. The next part is the ejaculatory duct and I mentioned ejaculatory duct is formed by the union of the duct of the seminal vesicle and the ampulla of the vas deferens and its main function is to deliver the sperm from the vas deferens and the seminal fluid from the seminal vesicle into the prosthetic part of the urethra. Now moving on to the urethra which is the next part and as I mentioned in the previous slide the there are three parts to the urethra the one that traverses the prostate gland is the prosthetic part of the urethra so the urethra is a continuation of the urinary bladder.

The main function is not just transporting urine it's not just part of the urinary system it's also part of the reproductive system it helps in transporting the semen along with the urine. So the the urethra starts with the urinary bladder and there is an internal urethral sphincter over there that helps in maintaining the flow of urine into the urethra and then you have part of the urethra that traverses the urogenital diaphragm that's over here that's called the membranous part of the urethra and then you have part of the urethra that traverses the penis also called the penile part of the urethra. Now that the duct system is done so we have learned the external structure that's the penis we've learned the scrotum and we've learned the ductal system.

Now moving on to the accessory sex glands so we have three types of accessory sex glands as you can see in this picture here so you have the primary which is the seminal vesicle and as I mentioned it's a paired structure you have a right and a left and then you have the prostate gland prostate gland is a single structure it's a midline structure and then you have the bulbo urethral glands the bulbo urethral glands are again paired you have right and the left and they lie on the urogenital diaphragm that you can see here and they open directly into the penile part of the urethra so these are the three sex glands so the seminal vesicle prostate gland and the bulbo urethral glands they're also called cowper's glands. I know there's a lot happening in this table but just to break it down a little bit and it is important for you to know the differences between each accessory glands and their function so we have seminal vesicle prostate gland and the cowper's gland or the bulbo urethral glands and as I mentioned the location size and structure seminal vesicle is posterior to the bladder lateral to the vas deferens whereas the prostate gland is inferior it's right below the bladder surrounds the prosthetic urethra and cowper's glands are at the urogenital diaphragm and they open into the penile part of the urethra the seminal vesicles are paired prostate gland is a single gland and the bulbo urethral glands again are paired very small glands. Now coming to the type of secretion this is important so this the secretions of the seminal vesicle are thick they're alkaline and they are fructose-rich seminal fluid so they are thick and alkaline because they need to protect the sperm that's deposited into the female reproductive tract into the vagina the vagina the environment of the vagina is acidic because of the production of lactic acid so to protect the sperm from this high acidity of the female tract it the secretions of the seminal vesicles are alkaline and the fructose is the major or the primary energy source for the sperm for it to keep for its motility.

So if you look at the major components of the secretions of the seminal vesicle as I mentioned fructose which is the primary energy source for the sperm for its motility prostaglandins so prostaglandins when it when the semen is deposited into the female reproductive tract the prostaglandins play an important role in contraction of the muscles of the female reproductive tract which help in pulling up the semen into the female reproductive tract basically movement of the semen into the female reproductive tract and that's the primary function of the prostaglandins and then you also have fibrinogen like proteins called seminogelin so this it is this protein that causes this initial coagulation of the semen when it is ejaculated so the semen when it is first ejaculated it's thick and viscous and that's mainly because of this fibrinogen like proteins called the seminogelin that is secreted from the seminal vesicle and as I mentioned alkaline pH to protect the sperm from the acidic environment of the female tract. If you look at the type of secretion and components of the prostate gland the prostate gland is milky and it's slightly acidic and it has zinc in it so the acidic nature of the prostate gland is contributed by citrate citric acid and also by PAP which is the prostatic acid phosphatase so these are the two components that contribute to the acidity of the prostate gland but overall if you were to see because the seminal vesicle contributes to 60 to 70 percent of the seminal plasma the pH is alkaline even though there is an acidic contribution from the prostate gland. The prostate gland also secretes PSA that's the prostate specific antigen and also proteolytic enzymes and these two are very important to liquefy the coagulant that is formed so the coagulation that's because of the secretions from the seminal vesicle if you were to leave the semen for a period of 10 to 15 minutes it slowly starts to liquefy and this liquefaction is because of PSA and proteolytic enzymes present in the prostate gland.

Coming to the secretions of the bulbo urethral glands it's mucus it's the main contribution is mucus secretion and it also has some bicarbonate for the buffering action and a major contributor is this seminal vesicle 60 to 70 percent of this the semen and then 20 to 30 percent is by the prostate and very less less than one percent is by the bulbo urethral glands. Primary function just to recap I already mentioned but the primary function is for the seminal vesicles it's providing nutrients as I mentioned fructose which is the primary source energy for the sperm alkalinizes the semen to protect it from the acidic environment of the vagina also aids in sperm motility and viability by keeping it in the coagulum and keeping it alkalinized. Functions of the prostate gland it helps in liquefaction of the semen because of the presence of PSA and proteolytic enzymes it also helps to stabilize the chromatin in the nucleus of the sperm and this is provided this function is provided by zinc so the zinc helps and stabilizes the chromatin of the DNA and also provides antimicrobial function.

The bulbo urethral glands main function as I mentioned is mucus secretion so it helps in lubrication and the pH buffering action helps in neutralizing the acidic urine residue during the process of ejaculation because urine again is acidic and urine again it since it passes through the same pathway bulbo urethral glands provide some buffering effect to neutralize the acidic effect of the urine. Clinical relevance and effect of removal of these glands so any abnormalities that can affect these glands be it infection, inflammation, and obstruction you will eventually have in terms of seminal vesicle you will have low semen volume because it contributes to 60 to 70 percent if there's an obstruction you should immediately think of you know if the patient has a low volume of semen you should immediately think of an obstruction to the seminal vesicle and if the obstruction is above the level of the prostate gland your ejaculate could be acidic because you only have the prostatic secretion and you don't have the seminal vesicle secretion and if you find low fructose in your semen then there's an obstruction at the level of the seminal vesicle and that's why there's no fructose in your ejaculate and if you don't have fructose and if the ejaculate is acidic then obviously it is going to affect your sperm motility. For the prostate again benign prostatic hypertrophy, prostatitis which is infection inflammation of the prostate it can be prostate cancer you could have had a surgery for your BPH it can all lead to scarring or obstruction can lead to ejaculatory dysfunction and altered semen liquefaction because the liquefaction of the semen is because of the secretions of the prostate gland and if you have problems with your mucous secreting gland then you have dry ejaculation increased urethral friction so basically painful ejaculation and emission.

So now we finished talking about the external reproductive structure that's the penis and the we've talked about the ductile system now we need to talk about the gonad itself the main the hero of the reproductive system so testis. Why know about testis? Infertility affects 50% of the couples but historically infertility the focus was mostly on the women but one third of the reason for infertility is because of male factor and success of an art cycle be it IUI or IVF it not just depends on the egg quality or age of the egg it also depends on the sperm quality. So before we begin with the testis I would like to give a brief overview of the structure of the testis.

So the testis is covered by three structures the tunica vaginalis which is the outer structure so going from outer to inner the outer structure is the tunica vaginalis it's a serous sac it helps it's fluid it helps in easy movement of the testis within the sac. Tunica albugenia is a thick fibrous coat and it sends in septa inside the testis which divides the substance of the testis into smaller areas called the lobules as you can see here the one highlighted in green those are the septa coming in from the tunica albugenia dividing the testis into lobules and then you have the very the innermost layer which you can see here is the tunica vasculosa so the blood supply the arteries and the vessels they form a plexus around the testis which is the tunica vasculosa. I know we are closing to the end of the one hour so I'm going to speed it up a little bit so the internal structure of the testis you can see it's divided into lobules by the septa and each testis has around 250 to 300 lobules and each lobule has these lobules they have the semipherostibules and each lobule has one to four semipherostibules as you can see here they are highly coiled structures present inside each lobule and each semipherostibule if you were to straighten it out it measures 30 to 80 centimeters long so you can imagine how tightly coiled and packed they are within the testis.

Now these semipherostibules they open into the hilum of the testis also called the mediastinal region of the testis they open into tubules called tubuli recti, recti meaning straight, tubule meaning tubules so they are straight tubules that they open up into the mediastinum of the testis and they form an interconnecting network of channels called the retetestis so this plexus that you see here in brown which is formed by these tubuli recti or the retetestis and the retetestis together again form the efferent ductules so the efferent ductules connect the testis to the epididymis so the efferent ductules each testis has 10 to 20 efferent ductules and they connect the retetestis to the epididymal head. If you were to take a semipherostibules cut it and look at the cross section this is what you would see it's a highly organized pattern of cells so this the outer wall of the semipherostubules that's also called the basement membrane and from the basement membrane you see a highly organized arrangement of cells so along the basement membrane is where you have the most immature germ cells which is the spermatogonia and then next to the spermatogonia you and as you progress to the lumen you have more advanced stages so starts with the spermatogonia then you have the spermatocytes then you have the round spermatids and eventually you have the mature looking spermatozoa with its tail protruding inside the lumen so this is present inside the semipherostubule and if you were to see in the interstitium that's outside you see these cells called the interstitial cells whereas the inside has the sertoli cells the one colored in purple so these are the sertoli cells and the ones colored in blue are the germ cells so the spermatogonia that will eventually give rise to the spermatozoa so the structure looks like the sertoli cells and the germ cells are present inside the semipherostubules whereas the interstitial cells as the name suggests it's present in the interstitium so it's outside the semipherostubules and it's also called the interstitial cells of Leydig and these sertoli cells are interspersed amongst the germ cells inside the semipherostubule. So again a close-up of the sertoli cells and its junctions so you have sertoli cells here and you see that the adjacent sertoli cells are larger cells so they extend all the way from the basement membrane up to the lumen and they are connected to each other the adjacent sertoli cells are connected by tight junctions and these junctions between adjacent sertoli cells is what forms the blood testis barrier and why this blood testis barrier is important it has two important functions so the blood testis barrier it splits the compartment into two one you have the basal compartment and then you have the adluminal compartment which is close to the lumen so it's called the adluminal compartment and the basal compartment as you can see it only houses the spermatogonia and the adluminal compartment has the primary spermatocytes secondary spermatocytes spermatids and so on and the lumen has the late spermatids and the spermatozoa so as I mentioned the blood testis barrier it has two functions one is for it to provide it's an immunological barrier so the sertoli cells they prevent because of this cell junction they prevent any interaction between the circulatory system of our body and then the cells of the the meiotic products which is spermatocytes and the spermatozoa so these spermatocytes and the spermatozoa are protected from the circulatory system and it's you know the immune complexes because these cells they carry antigen which are produced later in life and they are not recognized by the body and to prevent anti-sperm antibodies from attacking our own cells the blood testis barrier needs to be intact.

The other function is it provides a specialized micro environment for the spermatogenesis to happen so it basically supports this the spermatogenesis system and the disruption of the blood testis barrier can happen in in case of infections trauma surgery heat stress as I mentioned varicocele in the slides before it can be because of chemotherapy for cancer treatment environmental toxins like smoking all these can disrupt the blood testis barrier and if the specialized cells like the spermatocytes and spermatozoa are exposed to the circulatory system it causes a immune reaction and the consequences can be an autoimmune architis germ cell apoptosis oligospermia or eventually aspermia. So again this is a brief differentiation of the different types of cells within the testis the germ cells sertoli cells and lytic cells just to give a brief summary of what I've put here so the germ cells are present inside the 71st tubules their main function is for it for them to undergo mitosis and meiosis and for the process of spermatogenesis the sertoli cells are also present inside the 71st tubules their main function is to form the blood testis barrier and also to support the developing sperm the spermatocytes so they're also called supporting cells sister cells or sustentacular cells because they help to support and nourish the development of the germ cells. Their secretions are primarily antigen binding protein inhibin b anti-mullerian hormone as I mentioned in the fetal stage and the hormones will be discussed briefly in the next lecture eventually which will be provided by inning and then the lytic cells are present outside of the 71st tubules and their main important function is the secretion of testosterone.

This is the arrangement of the cells within the 71st tubules you have the spermatogonia at the basement membrane then you have primary spermatocytes, secondary spermatocytes, round spermatids and then the elongated spermatids and eventually the spermatozoa and this arrangement of the cells is called a spermatogenic wave once a spermatogonia develops it forms into a spermatozoa you have another cohort of spermatogonia that develops into the spermatozoa and this keeps happening and this is called a spermatogenic wave. So coming to the spermatogonia you have two types you have the type A spermatogonia and the type B spermatogonia. So the type A spermatogonia is again further subdivided into type A dark and type A pale.

Type A dark is the spermatogonia which is it multiplies but it's more silent it's the major reservoir it forms the reserve cells there's no active mitosis happening to the type A dark spermatogonia and the type A dark spermatogonia differentiate to form the type A pale and these are the ones that are actively multiplying actively dividing and help to maintain the reserve the pool of the stem cells that is necessary for future spermatogenesis. And the type A pale because of its division it gives rise to the type B spermatogonia and once type B spermatogonia is formed it's committed to differentiation committed to forming a spermatocyte and there's no looking back. So it's type A that's constantly renewing itself mitosis and once type B is formed it differentiates into this primary spermatocyte.

Moving on to spermatogenesis proper most of you are aware of this topic so I will be a little quick. So the spermatogenesis you have you have these four phases first is the mitotic phase which is also called the spermatogonial phase where you have a constant duplication of or mitosis of this type A spermatogonia and then eventually differentiation into the type B spermatogonia and then which differentiates into this primary spermatocyte. So up until this point up to the point of primary spermatocyte it's all mitotic so it's 46 chromosomes.

After primary spermatocyte is formed that's when the next phase happens which is the meiotic phase and now meiotic phase is again divided into two it's meiotic my part one of meiosis meiosis one and then meiosis two. Meiosis one is the actual reductional division this is where the 46 chromosomes actually gets reduced to 23 chromosomes. Meiosis two is does there's no further reduction the 23 chromosomes stays the same and I will explain why you have two parts to it then if it's already reduced to 23 chromosomes in meiosis one and then so that part is meiosis.

Then the next phase is spermiogenesis so now that you have the products of meiosis which is the spermatid the spermatid needs to undergo structural changes for it to look like the mature sperm and that process is called spermiogenesis so the structural changes that happen from a round spermatid to an elongated spermatizoa is called spermiogenesis and once the spermatizoa is formed it's expelled into the lumen through the process of spermiation and then into the efferent ductules and then the head of the epidermis which is the spermiation. So this is just to quickly explain why you have two reduction division so as you can see here so this is the primary spermatocyte which is still 46 chromosomes but you need spermatizoa to be 23 chromosomes for it to fertilize an egg which is also 23 chromosomes to form an embryo that's 46 chromosomes. So when the primary spermatocyte before the first meiotic division happens so this is 46 chromosomes for the ease of understanding it's just one pair of chromosomes here which is 46 or 2n at this point there's DNA replication so it's still 46 chromosomes but the DNA quantity is doubled so there is double there's a replication of DNA so there's double the quantity of DNA in it but still it's 46 chromosomes.

Now when the first meiotic division occurs so this is the reduction division now you have 23 chromosomes but again the DNA quantity is double so double the quantity of DNA but still 23 chromosomes and now in the second meiotic division that's when even the DNA quantity gets halved so you have four daughter cells each having 23 chromosomes and single quantity of DNA so that's why you need two meiotic divisions first to reduce the DNA the chromosome number the first meiotic division and second meiotic division to reduce the DNA quantity the quantity number. So the primary meiosis the primary spermatocyte is the cell that goes into primary meiosis it's the longest phase takes up to 24 to 30 days reductional step 2n to n as you can see here it's 2n but double the quantity of DNA four chromatids and then meiosis 2 secondary spermatocyte enters into meiosis 2 this is a very short-lived process it takes place over 24 hours and here you have reduction in the number of chromosomes and then eventually the DNA content gets reduced. So now that the spermatids are formed next process is for the round spermatids to undergo spermiogenesis so it's a where the round spermatid forms an elongated spermatizoa and this process is called spermiogenesis and then you have four different phases you have the Golgi phase you have the CAP phase you have the acrosomal phase and you have the maturation phase.

So in the Golgi phase before we begin so you see these structures here so this yellow structure is the Golgi apparatus and then you have the mitochondria and then you have these two structures which are the centrioles so there are two centrioles eventually will form the proximal centriole and the distal centriole. So in the Golgi phase the Golgi apparatus starts to produce vesicles called the pro-acrosomal vesicle and they all coil sorry and they all coalesce to form a single vesicle called the acrosomal vesicle which is shown in blue here. So the formation of this acrosomal vesicle is what happens in the Golgi phase and then the microtubules migrate to the lower pole of the nucleus so this is the upper pole or the nuclear pole and this is the posterior pole of the nucleus this is the anterior end of the sperm the posterior end so the micro the the centrioles migrate to the posterior pole of the nucleus and the acrosomal vesicle arranges itself in the anterior end of the nucleus so this is what happens in the Golgi phase.

In the cap phase the acrosomal vesicle further elongates to form a cap around the nucleus that's why it's called the cap phase and then this the centrioles are now at the at the posterior pole the proximal is closest to the nucleus and the distal centriole starts to elongate eventually giving rise to the flagellum of the sperm. In the acrosome phase you have the acrosomal cap still elongating but in this phase more importantly it's the nucleus that's starting to change its shape and this changing shape of the nucleus is contributed by the Manchetti formation you can see it in red here right next to the nucleus and these are temporary microtubules they help in shaping the nucleus into how the nucleus eventually looks like a pear-shaped or word-shaped structure inside the sperm head. So these Manchetti formation happens in the acrosomal phase and the nucleus starts to get a pluriform shape and the mitochondria starts to arrange itself along the sheath in the midpiece as a mitochondrial sheath and eventually in the maturation phase any remnant of the cytoplasm is extruded out as a residual body and it is phagocytosed by the sertoli cells which is the surrounding cells next to the developing germ cells and then eventually the mitochondria is forming a mitochondrial sheath in the midpiece and then the centriole forms the flagellum of the sperm and the acrosomal cap gives rise to the acrosome and then the nucleus is formed and the chromatin inside the nucleus it's highly condensed and tightly packed to protect the DNA.

So timeline of the spermatogenesis, so the entire process it takes about 74 days from a spermatogonia to a spermatozoa and then it takes an additional two to three weeks for this spermatozoa that's you know produced from the testes for it to undergo maturation. So the total time for it to appear from the spermatogoa up until the ejaculate it's about 90 days. The clinical relevance if a patient has been exposed a toxic exposure like a fever or infection you will not see the sperm deterioration immediately.

Let's say the patient had fever today the next day his ejaculate probably still will be the same but if it has affected the spermatogenesis you will be able to see this 90 days after because it's as I mentioned it's a spermatogenic wave it's a moving train so for it for the effect to happen and for the effect for you to see it it takes about 90 days or two to three months later. The last we are winding down so the last is the ejaculation and its neural control the stages of ejaculation is two parts emission and ejaculation. So emission is just the movement of semen into the posterior urethra into the prosthetic part of the urethra so from the seminal vesicle ampulla ejaculatory duct and into the urethra whereas ejaculation is the expulsion of the semen out of the urethra in into the female reproductive tract in case of copulation.

So the clinical relevance of this is the emission part is a sympathetic control the nervous system is a sympathetic nerves the T12 to L2. If the patient were to have any spinal injury affecting these nerves the sympathetic innervation is affected and this can cause retrograde ejaculation. Why? Because when the vas different contracts the internal urethral sphincter that's right on top here that I mentioned before it needs to close.

So it's the contraction of the ductal system and the urethra but the internal sphincter needs to close because the the semen needs to go out and not back into the bladder. But if there's the nervous system is affected then there is a retrograde ejaculation the sperm goes into the urinary bladder and the acidity of the urine compromises the sperm and you don't have either you have azoospermia or if you were able to collect the sperm from the urine the sperm is at that point either dead or immortal. So two parts to ejaculation emission is movement of semen into the urethra and ejaculation is forceful expulsion outside.

Composition of semen as I already mentioned before so it has two parts the cellular component and then the seminal plasma which is the liquid component. So the cellular component it only contributes to five percent of the volume but the majority 95 percent of the seminal semen volume is contributed by the fluid secretions of the accessory sex glands and as you can see here the majority is by the accessory sex glands but only a tiny portion is contributed by the sperm cells and majority being the seminal vesicle next being the prostate gland and then being the cupper glands. So this is the end of part one I know it was a lot I hope you're still ready for the next part I have a few knowledge check questions for you if you would like to participate.

So in the first diagram the one highlighted in green if you can unmute yourself or type the answers in the chat box I would appreciate that. What is the part highlighted in green in the first picture anybody? I don't see the chat if anybody is able to please view the chat for me I think that would be helpful. Okay the part highlighted in green is the testis.

Okay don't be shy guys. Moving on to the next picture what is the part highlighted in green? The lobules of the testis. Yes perfect thank you Joseph and in the next picture what is the part highlighted in green? Septa.

Yes that's good very good I'm glad okay so that's the septa of the testis perfect. Moving to the next question which structure is responsible for storing and allowing the maturation of spermatizoa before ejaculation? That's an easy one don't be shy. Should be the epididymis.

Yes thank you that's the epididymis. As I mentioned the body of the epididymis is where the maturation takes place and the cauda or the tail of the epididymis is the primary storage that's the primary storage area for the sperm. Which gland contributes to the highest volume to the semen? The seminal vesicles.

Yes 60 to 70 percent of the semen is contributed by the seminal vesicles. Good job. Kelsey I personally can see the next slide so I always know what the answer is if even if I walk to it but I can see the next slide I don't know if anybody else can.

These are easy questions I'm sure that they actually know but I'm just telling you I personally can see the next slide. I mean we can but it's not the correct answer is still not highlighted. Yes okay yes and I purposely made the questions easy.

Perfect. All right so the next one it's a clinical scenario. A 22 year old man with a history of unilateral undescended testis corrected at the age of five presents with subfertility.

Which explanation is most accurate? Remember undescended testis? Anybody? Well now we see the correct answer on the other side of the screen. I see what you mean. I was between B or C. Yeah there you go it is testicular disgenesis because of the heat exposure.

So undescended testis if the testis is still within the body cavity it's at 37 which is not good for spermatogenesis and even if it was corrected at the age of five that's five years gone with you know causing damage to the small tachycardia cells. So it's testicular disgenesis because of the heat exposure which impairs the germ cells. So history of undescended testis is a very important history.

Can I make a short comment about that question? I see Joseph why you were going between B and C because B is legit actually it can happen. But just with that in mind that you are planning to take your HCLD test and I'm assuming others may want to take a TS at some point at least. It's important to understand that at that test you may have two correct answers and they're just looking for the best answer.

So this question actually is very good in that sense. Choose the best of the best. Yeah.

Okay the next one hopefully you can see the answer to this one now. A 32 year old man presents with infertility. Semen analysis shows low semen volume, acidic pH, that should ring a bell, and normal testicular biopsy.

Which condition best explains his findings? Be concerned for an issue with the prostate? Low semen volume? I mean you're having an issue with the seminal vesicle because of the low seminal volume and acidic pH. But wouldn't that be coming from the prosthetic enlargement? The acidic pH meaning it's not alkaline so the prosthetic secretion is still normal. But if only if it was normal semen volume with acidic pH then it could you know be a prosthetic hypertrophy.

But in this case there are two key points low semen volume and acidic pH. So the answer is it has to deal with the seminal vesicle. So it's an ejaculatory duct obstruction.

So if there's an obstruction at the level of the ejaculatory duct you don't have seminal vesicle secretions first contributing to the volume. And because there's no alkalinity whatever normal secretions are there from the prostate it's acidic. So that's it.

So it's okay I understand now. Yes. The last one the 28 it's a 28 year old man presents with infertility.

Semen analysis shows low semen volume, absent fructose. Which condition is likely the reason? Again. C bilateral.

Yes good job. So it's low semen volume so seminal vesicle obstruction and no fructose in your ejaculate so something to do with seminal vesicle obstruction. So you're correct.

Thank you Andrea. And that's it. I'm sorry I went over a little bit but if you do have any questions please reach out to me that's my contact.

I'd be happy to help you. Thank you. Thank you Kelsey.

I think this was an excellent lecture and a good refresher for all of us. So thank you so much for that. We did go over but I think it's all for the good cause.

So hope you support that. So now we will go we will get to the next lecture but first if you need a bio break for a few minutes that's fine too. So just either say yes or we will just continue.

Okay I don't see any emergencies. So okay it's your turn now. Can you see my slides? Yes we do.

And you may want to go to the presentation mode. Yes. Perfect.

Perfect. Can everybody hear me? All right. Okay.

Are you all overwhelmed by the lecture about the physiology? And I hope that the endocrinology part is less confusing and everybody can walk away with good knowledge about how hormone regulates our male reproduction. So again my name is Eileen Li. I'm currently a senior urologist at Palo Alto Medical Foundation.

And this is our learning objectives. So first of all at the end of today you should be able to first describe the role of HPG axis in the regulating of male reproductive function to differentiate the synthesis and secretion of FSH and OH by the pituitary gland. And you should be able to identify the target cells by FSH and OH and how they collaborate to support the spermatogenesis and testosterone production.

And also you will be able to interpret how those disruptions within the HPG axis can lead to the clinical impact of male infertility. I know that I use a lot of acronyms here and don't worry if you have no sense of what is HPG, what is FSH and OH. I guarantee you will understand everything and you have a good knowledge of the endocrine system.

All right so let's start with a very simple question and since we are talking about endocrinology, what are hormones? What is the hormone to your understanding? All right to my understanding hormones are, since we know as embryologists we all know that we all develop from one single cell. Then we start the differentiation. We all start from there like what we observed in the lab.

And then we ourselves decided okay I want to be the pituitary gland, I want to be the ovary or testes, I want to be whatever the foot, the nails, whatever. Then all the organs they start to grow apart from each other but they are still collaboratively, collectively to work for us, our human body. Then how they talk to each other since they are so apart from each other but they want no one to eat taking into control of each other.

So that what they do, our body is so smart. So they secret some messengers and those messengers are called hormones that allow us even we're adults, our organs are taking apart but they can still communicate. They're taking controls, place orders and to talk to each other so they are not in our body.

Okay the hormones, how they travel, those messengers depends on the distance. They can travel either in our bloodstream, relatively when they travel a little bit further distance, they travel through the bloodstream because it's circulating throughout the body. And in this scenario those are called endocrine systems, the pathways.

And the cells when they maybe within the same organ and the cells want to talk to each other, they can just defer into the peripheral and talk to the neighbor cells. And in that pattern, this is called paracrine system. And sometimes the cells also talk to themselves and if they do that, this is called autocrine system.

Okay so this is the three ways the hormones are secret, they are travel. All right so what is related to reproduction? We have mainly, we have more actually, but we mainly have three types of hormones in our body. It depends on the size, the smallest one are called peptides.

Normally the peptides have the, they are small molecules, they only have a very small, a certain number of amino acid. And for example, and we will talk about in details, that's the GnRH or gonadotropin-releasing hormone. And some of the hormones they are slightly larger.

Those are the glycoproteins. They are larger amino acid chains with the sugar unit or called carbohydrate groups. And those are the hormones, for example, is the follicle-stimulating hormone or FSH or luteinizing hormone, LH.

And some of the hormones, they are really big. They are steroids. They are hydrophobic.

They don't like water. They will be isolated from water units. And they are mainly coming from the gonads and they are called steroids.

All the steroids are derived originally from cholesterol. And we will talk about the conversion from cholesterol to our steroid hormones. It depends on mainly, depends on the size of the proteins or the peptides or steroids.

They have different half-lives, meaning they can sustain in our circulation for different times. With the shortest half-life are the peptides. They're within minutes, they will be gone.

And then followed by glycoproteins, so FSH and LH. Those are gonadotropin hormones. They are glycoproteins.

They can stay somehow longer than the peptide hormones. And the longest sustaining hormones are the steroids. They can stay for a really long time, sometimes can over a day.

And hormones or messenger molecules, they don't have to travel alone. Although they are having a mission of talking to the other organ, but they don't have to travel alone. Sometimes they have chaperones and the chaperones are called protein bonds, binding proteins, and they can travel together with the messenger and to work to the next target organ together.

Okay, so then the hormone I reached to, let's say, for example, the ovary wants to talk to the head. Now, when they reach to the target organ, what they do? They have to bind to their specific receptor. And the binding of this messenger hormone, the hormone right now is called the ligand.

The ligand binding to their specific receptor, just like the key and the lock, you have to find the right key to open up the lock and the trigger the following cellular event. Use the wrong key, meaning if it's a wrong messenger, it will not bind or unlock. So there will be no following cellular events.

All right, so then we understand what is hormone. Then let's talk about the entire human body that is regulating our reproductive system. That is the HPG axis.

That's the first acronym you will need to remember at the end of the day, the HPG axis, what that's representing for, hypothalamic, pituitary, and the gonadal axis. And by the name, we already know there are three organs involved. First, from the height, your head is the hypothalamus, and then the hypothalamus is part of the brain.

There are neurons in the brain, and the neurons is called gonadotropin-releasing hormone neurons. Those are the neurons will secrete the molecule or the messenger called gene nourish, gonadotropin-releasing hormone. Then they will connect this organ to the next one called pituitary gland.

It's a very small but very functional endocrine gland called pituitary. The pituitaries will secrete the gonadotropins, follicle-stimulating hormone, and luteinizing hormone. Once these hormones are secreted, when released from the pituitary gland, they will travel down through the blood system.

So the endocrine system goes to the gonads. And of course, for the male part, those are the testes. And for the female part, those are the ovaries.

Then the ovary will talk back. They do not only receive messages, they also talk back to the head and the pituitary gland. So those are the feedback effects.

Okay, it can be either positive or negative. Okay, so let's start from the top part. That's what is in the head, the hypothalamus, the gene nourish.

Gene nourish is the fundamental of our reproduction. In fact, the discovery of gene nourish has been awarded the Nobel Prize because of the discovery. And this is, to my knowledge, the first time that something was discovered in the reproductive field and awarded by Nobel Prize.

And actually something before was also awarded Nobel Prize is the discovery of testosterone and estrogen, but that is in the chemistry field, but not in the reproduction or physiology part. Okay, so as the discovery of gene nourish was because there's a big misery in our reproduction, that's the onsite of puberty. We know that we grow and then what triggers somehow in our teenager stages, we become adult, our reproductive system become mature.

And this is because of study and doctors Gilman and Sadi discovered gene nourish. And they find that the gene nourish was a very small molecule. It contains only 10 amino acid.

So gene nourish is called dicapeptide. The gene nourish was secreted at the nerve terminal from the hypothalamus and was released into the median aminin. That is the part connected hypothalamus to the pituitary gland.

And then will reach to the pituitary gland and binds to the gene nourish receptor located inside the pituitary gland to stimulate the two gonadotropin productions. The cells that secrete the gonadotropin production are called gonadotropes. And they are both located in the anterior pituitary.

And we will talk about this. Okay, gene nourish is not in the hypothalamus since the beginning. Gene nourish need to travel.

And when we were doing our development stage, actually there was about the 5th to the 16th embryonic week. Gene nourish initially in the gene nourish neuron precursors, they start from our nasal area. So the nasal area is the olfactory placode.

Gene nourish travels outside of the central nervous system in the olfactory placode. And then they will start to travel along with the neurons to go from the olfactory bulb and terminals until they end up with the nasal septum. Then they will travel until it's reached to the hypothalamus as their destination.

Once gene nourish arrives at the hypothalamus, they will immediately take in function. Okay, so the gene nourish can start to be detectable starting from maybe 13 to 15 weeks of embryonic week. And then gonadotropin, which is stimulated by the gene nourish can be detected as early as 16 weeks.

So they are gene nourish migrates from the olfactory nasal area, and they travel to the hypothalamus and taking effect immediately. And I want you to remember this because the early onset of gene nourish is essential. Okay, so what if the migration, there's something wrong with the migration? So this is one of the clinical syndrome is called common syndrome.

And this is largely due to the failure of gene nourish neuron migration. Okay, so if the neuron migration, do you see my mouse? You can, can you see my mouse? If I do, okay, perfect. So if the migration didn't happen, something is wrong with that.

And this is a case report. We have this male and we call the male or XY individual because his keratotype is 46XY. It's a normal XY individual.

His clinical, he's 44 years old at the time of this report. His serum FSH, LH and testosterone levels are all low. Okay.

And we can see that he lacks of facial and body hair. He has a severe gynecomastia. So he has a relatively bigger breastbone.

He's relatively obese. He has decreased muscle mass. So that's not typically a male shape.

He has a very small penis. He has right side cryptorchism. And I think that because he just talked about the descending of testes, it's called the cryptorchism.

Actually, this is related to gene nourish migration. And he has a decreased libido and erectile dysfunction. And this is closely related because he has a low testosterone level.

And his brain EMR shows that he has an olfactory bulb hypoplasia. Okay. That's why the gene nourish neuron was not migrated successfully.

And very importantly, and what is the signature of this syndrome is anosmia. So those patients, they do not smell things. Okay.

Because where gene nourish come from? The nasal area. Okay. And this Kalman syndrome was also first described by Dr. Kalman in 1930s.

Okay. So gene nourish is so important. Is gene nourish the beginning of everything? As I said that gene nourish was discovered in 1970s.

And only until the last, probably the last decade. Something else showed that these are the things actually control gene nourish. Also in the brain.

Those are the kiss peptides. Kiss peptide control the release of gene nourish. Okay.

Gene nourish, how gene nourish is secreted? So gene nourish, again, gene nourish are the neurons in the hypothalamus. And people find that the way recent discovery find that the gene nourish has a two kiss peptide neuron populations located in the hypothalamus control gene nourish release. One population is located in the ABPV and POA, or this is anteroventral, cariventricular nuclear and a preoptic area.

This area of kiss peptide neuron control the gene nourish and trigger the gene nourish surge. And this will be only for the female specific. And we'll talk more details next month when we talk about hormone regulation of female infertility.

At this time, because we focus on the male part, let's talk about the other population. This population of kiss peptide neurons, they are located in the accurate nuclear or the ARC area. This location, the kiss peptide in this area has a very sweet name called candy neurons.

Okay, the candy neurons, the brown one here, indicated here, connected directly to gene nourish neurons. And the candy neurons making gene nourish to be released in a pulsatile format. And the pulsatile release of gene nourish is the fundamental.

It cannot be more important. It has to be released in a pulsatile format. So the pulse frequency in the females is depends on the cycle stages.

We'll know that female has menstruation, menstrual cycle. Depends on the cycle stages, the pulse frequency can be between 0.5, half an hour to six hours in females. While in males, because males, they do not cycle, it's a more consistent frequency, about two hours in males.

And this kiss peptide neurons in this area applies in both males and females. And let's see why gene nourish pulse frequency are important. Okay, before that, so what we talked about, so that we know gene nourish and gene nourish neuron, release gene nourish peptides into the median aminin or the ME.

And that they will travel through the pituitary to reach to their target cells called the gonadotrope cells, located in the anterior pituitary. The pituitary gland is very small. The pituitary gland is only of a bean shape, but this is one of our major endocrine organ.

The five main types of cells in the pituitary gland, actually the pituitary gland has two lobes, but we'll only talk about the anterior, so the front one, which I highlighted in purple. The posterior pituitary is more of a nerve organ, so we are not talking about this. This is not related to reproduction at all.

In the anterior pituitary, we have five cells. The first one is called the corticotrope. They secrete the corticotropin hormones, and we know this is the hormone that's in response to your stress.

And the second cell type is called somatotropes. Those are the cell types secrete growth hormones. This control how tall we will grow.

And another one is the therotropes. It's creating thyroid stimulating hormone, TSH. And we know that TSH, it has been a debating of the level of TSH related to especially in female reproduction, but this is more important for our digestion system.

And the lactotropes producing prolactin hormones, and it's for the milk production. And the end but not least, this is closely related to reproduction, are the gonadotrope cells. Those are the cells producing gonadotropin hormones, including both follicle stimulating hormone, FSH, and luteinizing hormone, LH.

So this is how important is the pituitary gland. We have to have an intact pituitary gland to support our gonadotropin production. So let's talk about the two gonadotropins that's closely related to reproduction.

First one, just as a side-by-side comparison, I put FSH and LH, they are very similar. They are very similar. So what they are by the side-by-side comparison, both of them are glycoprotein.

As I said that they are sugar unit proteins. They were both produced in the same cell type called gonadotropes in a pituitary gland. Actually, FSH and LH, they are structurally similar.

They even share a common alpha subunit. This is the function as one leg of the protein. This protein, both of them has two legs and they share one common alpha subunit.

And they have a unique beta subunit. So FSH beta subunit and LH has the LH beta subunit. And the beta subunit making them different and making them work differently.

So this is, we said alpha plus FSH beta to make FSH, alpha plus LH beta to make an LH protein. And because I just said that they are sugar units on these proteins, so they are glycoform dependent. It depends on the size of the protein.

It can have a different serum half-lives. FSH has a longer half-life, about three to four hours in the circulation. While LH has a shorter half-life, only about 20 minutes.

So FSH and LH, they are both synthesized and secretion is controlled by GnRH. So the GnRH release can control both of them. And you must be questioning if they are controlling both of them, how GnRH knows which one to make.

And in addition to GnRH, FSH alone can also be regulated by a pituitary local factor called activin. Well, but I'm not going to talk about this activin today, but I want you to understand that FSH can be stimulated by both GnRH and another factor called activin. And we will talk about the counterpart of activin actually in this lecture.

Well, LH is mainly regulated by GnRH. FSH and LH are stimulated, gene expression are controlled by both GnRH. FSH and LH are both genetically expression is controlled by GnRH, but they are secreted in different formats.

FSH is more in the constitutive and regulated secreted pathway. What does that mean? That means FSH was made in the pituitary cells and immediately will be released. Whereas LH are made and they are stored in the pituitary cells until they receive a further instruction and to release as a pulse.

So what does that tell you? LH is also secreted in the positive format, while FSH is more in the constitutively released format. And this is an immunofluorescence study and it's probably by me. Again, this is a pituitary tissue and the red of the immunofluorescence staining, staining for the cells that express FSH and the green are the cells express LH.

And to put the two images together, you can find that they are perfectly aligned. Wherever makes FSH, that cell also makes LH. All right, so FSH again, how GnRH regulating FSH and LH? Again, GnRH binds to the receptor called GnRH receptor.

This is a GPCR. I know it's probably too molecular based and you don't understand, but you don't have to. Once GnRH binds to the receptor, a trigger of following a series of cellular events.

And GnRH will stimulate the direct expression of the CGA, which is the gene coding for the R4 subunit, the LH beta subunit and FSH beta subunit. And again, FSH is more released in the constitutive pathway. So FSH was made, this is the nuclear, so it's gene expression, then it will move to the cell and then FSH will be released immediately.

LH is after the gene expression, the LH will go out of the nuclear to make LH protein. When LH was made, it's more storaged in the, they call it a granule, like the pouch, and it stays right beside the cell membrane until a further stimulating signal to be released in the positive format. So as I said that since both FSH and LH are regulated by GnRH, how GnRH specifically regulate and how GnRH knows what to make.

Either FSH or LH is based on the pulse frequency. The faster GnRH pulses, so fast, fast, fast, fast, the pulse frequency make more LH production. While GnRH pulse is slower, however, still in the posit L, but slower than GnRH favors the FSH production.

And again, very importantly, GnRH has to be released in a positive format, and we will talk about this in the next slide. So we see that from this figure, this is already a known knowledge since 1980s. If we give the GnRH one hour per pulse, so in the one hour per pulse frequency, GnRH make more LH production, but less FSH.

When you give a less frequent, so one pulse per every three hours, now you will have more FSH, but less LH. Okay, when you give it back to the same frequency one hour per pulse, GnRH will stimulate more LH production. Okay, can you, if GnRH regulates both FSH and LH, and they are both important for reproduction, can you constitutively or continue to give GnRH? The answer is no.

As I said that, it's gonna have to be in the positive format. If you give FSH, so the green are LH, and the red are FSH. If you give positive GnRH, you have the both production of LH and FSH.

If you give a continuous stimulation, so constantly give GnRH, not in the positive format, you actually don't regulate both production. And if you give it back in a positive format, the production will resume. Okay.

So, once the gonadotropin are released, what they are traveling to? From the pituitary, I see the bottom part of our brain, and they will travel a little bit down distance to the gonads. That means the test is in the males. Again, this is through our bloodstream.

What happened over there? Now, FSH and LH have different missions, and I'm closely just to talk about this. So, this is the seminiferous tubules. This is where the sperms are made.

And the sertoli cells are located inside of each seminiferous tubules. Actually, the sertoli cells are the nutrient cells that support the spermatogenesis. And in fact, sertoli cells also give the frame of each seminiferous tubules.

Okay. And then FSH, actually, that's the target cell that FSH is going on. So, FSH reach to the testis, they will find this receptor expressed in the sertoli cells.

And what they do over there? First of all, FSH, that's why I'm saying that GnRH onsite during development is also important, because GnRH onsite during development will start to work and produce FSH. Those FSH will stimulate the proliferation of sertoli cells. Because once you reach puberty, your sertoli cell is not going to make any more.

The number is set. It's only during development FSH stimulate sertoli cell number and to make the, they call it spermatogenesis niche. That's the niche support for spermatogenesis after adulthood.

And there's a second thing that FSH does. In the sertoli cells, they will produce two things. One is the androgen binding protein, and we will talk about this later.

So, those are the proteins will bind to the androgen or testosterone. These testosterone, they will concentrate the testosterone into taking a more powerful event. Another thing that FSH does in the sertoli cells is to create another hormone, inhibin.

This inhibins, we will talk later, they will travel as a negative feedback factor to the pituitary to modulate FSH or LH. Okay, now let's switch gear to the LH. LH, once they reach to the testes, they work for something else.

They work on another cell type called leading cells. The leading cells will express the LH receptor. These are the cells, if you remember from Kelsey's talk, leading cells are the cells that for real make testosterone.

And the leading cell make testosterone is under the control of LH. Okay, so how LH make testosterone? As I said, testosterone are steroid hormones. They are made from the original cholesterol.

How cholesterol? Cholesterol is surrounding every single cell, and cholesterol need to go to this cell organelle called mitochondria. Cholesterol need to go from the cytosol to the mitochondria to be converted to progesterone, and then later on to convert it to testosterone. Is this easy? This process is relatively easy, but the most difficult part for cholesterol to be converted to testosterone is a limiting process, is how cholesterol to get into the mitochondria.

And this is where the contribution from LH. LH binds to the LH receptor, LHR, and can stimulate the first relation or a lot of cellular events. And again, I don't think it's necessary for you to know that what are the cellular events, the first relation of the proteins, but regardless, LH should contribute of making this star protein.

The star protein is the one who makes the cholesterol to come into the mitochondria to be converted to testosterone later on. Okay, so how LH support for testosterone production? LH stimulates star proteins, and that is the protein dragging the cholesterol into the mitochondria in order for it to be converted to testosterone. Alright, GnRH, LH release is really consistent with the GnRH pulses.

Once GnRH pulse, LH will be released. And we can see from the top figure, this is a normal LH pattern. When you have a regular GnRH pulses, LH also pulse.

And you have the testicular volume was 20. I don't know what animal, I'm so sorry. I don't think this is human being, but since it's 20 million, I don't know if it's human body.

And this normal sperm count is 70 million per meal. Let's see, what if you give a low amplitude, so it's a smaller pulses, then you have a smaller testicular volume, and you essentially almost have no sperm count. And can they have a pulsatile, so I continuously to give GnRH, then what happens? Continuous giving of GnRH result in the continuous release of LH, and those LH basically will not work.

The LH will have a low testicular volume and low sperm counts. And that's what the reason is called, this is a system mechanism is called receptor internalization. I'm not sure if you're familiar with that.

So once you have the ligands, it will bind to the receptor. Each cell have a certain amount of receptor. You can't continuously constantly use that receptor.

You need to give that receptor a break. That is called the receptor recycling. You give the ligand, bind to the receptor, the receptor will come into the cell and to trigger the cellular events.

But then you need to give the receptor some time, so the receptors can be recycled back to the cellular surface to take the next batch of ligands for stimulation. If you continuously to give ligands to bind to the receptor, then the receptor will say, okay, too much work. I just don't do it.

I will stay inside of the cells. And then later on, if you give more stimulation, what is going to happen? They will just not respond. Okay.

So next one, the testosterone. Testosterone is the main type of androgen. So when you are referring to androgen, we are referring to testosterone as well.

So testosterone are the sole protein that is absolutely required for spermatogenesis. As Todd Kelsey said, the spermatogenesis pathway, it takes about 90 days for the sperm to develop from the primordial germ cell to eventually become the mature spermatozoa. And the animal study actually in mice, they find that testosterone is not continuously required.

It's only required during the later stages of spermatogenesis. So if you don't have testosterone, you probably will have the spermatogenesis pathway stuck in the middle of somewhere like here, but you do not have the mature spermatozoa. Okay.

So now let's get to finish up this loop. The gonads, when the gonads receive the stimulation, now it's the gonads' turn to talk back to the pituitary level and the hypothalamus level. And this is called the feedbacks, what they want.

The gonads will talk to the upper part. Either they want more stimulation or they think that, okay, enough, I don't need more stimulation. That's it.

Okay. So first thing that travels back is the testosterone. Testosterone will go back to both the pituitary and the hypothalamus level.

And where are they going to bind? The testosterone receptor or the androgen receptors. And this is actually how kisspeptin was discovered. So let's see this immunofluorescence.

This is the kisspeptin in the ARC area. Again, this is the kisspeptin. Neurons are Okay.

So this is the kisspeptin expressing cells. And we see that the cells, the majority of these cells also express the androgen receptor. And that's the co-related, they are co-localized together.

So that's how, again, kisspeptin was found that testosterone travel back to the hypothalamus and then binds to kisspeptin receptor and to further regulate GNR release. Okay. Another thing that is less talked about, but it's equally important, if not more, the gonads also secrete another protein called inhibins.

And in fact, a male or a man only make one of the inhibins. So this is the male version of inhibin, the inhibin B. Then again, in my lecture, if you remember correctly, what cell make inhibin? The sartorii cells. Okay.

So the discovery of inhibin, just to make this lecture more interesting, it's also a good story. Inhibins are discovered in 1923. During that time, this was discovered by Sharon Diffie.

So inhibin was discovered that, so these are rats. The rat received radiation. And the researchers find that the rats that receive radiation and to destroy their testes, they will have a pituitary hypertrophy.

So that means, what does that mean? Something in the testes surprise the growth of the pituitary gland. Okay. That's why when you remove testes, pituitary gland will have a hypertrophy.

It will be over-enlarged. Again, this is a joke here. This is not the testes.

This is the pituitary gland. Okay. Although they look similar, but this is the pituitary.

Okay. So researchers first suspect, what is that thing? What is the thing that controls from the testes back to the pituitary? The first suspect is the testosterone. And to confirm whether it's testosterone, so the researchers in the next decade, what they do is that they give back those rats with testosterone to see if that rescue the enlargement of pituitary.

And they find there's no. And actually their research find that this molecule, though it's secreted by the testes, but again, testosterone is a steroid. It's hydrophobic.

It doesn't like water, but this molecule actually dissolves in water. And then it surprised the pituitary growth. So they don't know what it is.

They are thinking that I don't know what it is. Since it has the inhibitory effect, let's just call it the inhibits. So this is how random this inhibits are named.

And the inhibits actually, once the inhibits are discovered, inhibits were first originally thinking to be the male contraceptive target. And this research actually kills a lot of pharmaceutical companies and postdoc fellows to work on inhibits to try to control male fertility. They all fail miserably.

And one of the reasons is that they cannot even purify the inhibits out. Let's count this. Since 1923 until 1985, over 60 years, people cannot even purify inhibits out.

And the reason why later on they find that inhibits, first of all, there are multiple types of inhibits, two types, inhibit A and inhibit B. So, eventually, they figured this out in the bovine, follicular fluid in the female parties. But then inhibits also have a similar molecule called actin, which is taking the completely reversed effect with inhibits to control the gonadotropin products. So, that's how inhibits does not work for male contraception.

And inhibit A, this is a beautiful, very beautiful inhibit A. This is the structure of all this inhibit family. You can see this butterfly shape. And I'm showing you, I know we are talking about, again, male only, both female make both inhibit A and inhibit B, but male only make one type of inhibit B. So, inhibit B. And the reason why I'm only showing you here inhibit A is because we still don't know how inhibit B looks like.

I can only show you how inhibit A looks like, this beautiful butterfly shape. And these old researchers have already found that inhibits can dose-dependently antagonize FSH production. So, FSH is dose-dependently antagonized with the increase of inhibit concentration, but LH are not impacted.

That says inhibits are specifically and selectively antagonized FSH only. And again, this is by unpublished data. So, this is showing you inhibit B in the male party.

Inhibit B can dose-dependently antagonize FSH at the level of gene expression. Okay. So, we know that the inhibits are secreted by the sartorii cells.

What if the sartorii cells is a clinical implication, the clinical relevance? If you have sartorii cells, but they do not work, then what is going to happen? Okay. So, don't be misleading by the name of this syndrome for sartorii cell only syndrome. That means sartorii cells are there, but they don't work.

And what does it mean? Sartorii cells are there, but they don't make inhibits. And actually, sartorii cell only syndrome count as the majority of the male azoospermia, meaning the males does not make a sperm. And there's non-obstructive, meaning that all the tubes are intact.

They can transport the sperm. But still, the males are infertile, and they count the majority of the patient actually are called sartorii cell only syndrome. So, those sartorii cells, they only stay inside the seminiferous tubules, but they were not making impact functional inhibit.

So, those patients, they have elevated FSH because they don't have inhibit B feedback, but their LH and testosterone levels are normal. And currently, in the IVF, this is not absolutely no cure. Actually, most of the patients were conceived if we give a microtestis, so taking the sperm directly from the testis and perform ICSI injection.

All right. So, I know it's getting really late, so let's just quickly summarize what we have learned today. The integrity of the HPG axis is very important to the male reproduction.

First of all, we need to have a positive release of GnRH and have the properly sartorii cell and the leading cell function that are essential. Hormone patterns reveal the site of dysfunction. Okay.

So, if you have a different type of hormone levels, you cannot figure out which side is wrong. And we all learned that the GnRH is important, and the GnRH is controlled by another neuron called Kispeptin. Kispeptin neuron's positile release stimulate the GnRH pulses.

The pulse control both FSH and LH. If you give continuous GnRH, you actually downregulate gonadotropin because the receptors are not recycled back to work. LH and FSH are created by the pituitary gland in response to GnRH, but they have a different target in the testis.

FSH work on sartorii cells to support spermatogenesis, basically setting up the niche, determine the total number of sartorii cells in adulthood. And that is the niche that how the more sartorii cells that you have, the more nutrient that you have inside the testis. So, it's easier for the testis to make sperm.

And it also stimulates a production called inhibin B. That is one of the factors that has the feedback effect to downregulate FSH production by the pituitary gland. Another thing that we didn't talk really in detail, but FSH does do, is to create an inhibin-binding protein, or ABP. Sorry, androgen-binding protein.

The androgen-binding protein, the function of this protein is to concentrate androgen, or testosterone. On the other hand, the LH goes down to the testis and work on another cell type called leading cells. The main function of leading cells is to stimulate testosterone synthesis, which is the main hormone that males mate and is absolutely required during the process of spermatogenesis, especially in the later stage, to support the sperm to become mature.

The leading cell and sartorii cell need to work, collaborate together to maintain the production. The testis need to talk back to the pituitary and the hypothalamus level to further regulate the gonadotropin productions. All right, so that's the end of my lecture.

I tried to make it quick so everybody can go back and take a good dinner. Do you have any questions before we start the quiz? For the knowledge checks, you can open up if anything is confusing. I know that it's a complicated system, although it's only involved in three parts of our body, the head, the pit, and the gonads, but it still can be very complicated.

If you don't have any questions, let's start the quiz. First one. Again, you can unmute yourself and tell me what is your answer.

This is a simple one. Where do you generate neurons? Perfect, right? It's a nasal placoid, olfactory region, and then eventually, gRNA will migrate to the hypothalamus. Okay, next one.

Again, a simple one. Basic question. What is the main target in eggs of LH in the testis? What does LH do? Leading cell.

Perfect. Leading cell stimulates testosterone production. Okay, next one.

What hormone provides negative feedback to both hypothalamus and the pituitary level in males? Which one? Again, remember, both. Should be testosterone. Perfect.

Testosterone, and inhibiting B only travels to the pituitary again and only downregulates FSH production, and male does not even make inhibitin A. Okay, folate statin, I didn't even mention that. Sorry, one question. I was under the impression also that the brain aromatizes some of that testosterone into estrogen as well.

Estrogens are made from testosterone. Aromatase, if the enzyme works, wherever it works, it will convert testosterone to estrogen, but I do believe the main site of producing aromatase is in the gonads. I do not know if any hint.

Again, the brain study will be more difficult. I can't say never say never, but I do not believe aromatase is abundantly expressed or made in the brain. Okay, and again, we will be talking about estrogen when we talk about the female reproduction and the chronology next month.

That will be more complicated. Okay, let's play a game. Okay, this game is called what's wrong with him? Okay, someone showed up.

Low testosterone, high LH, high FSH, low inhibitin B. What's wrong with him? Some sort of primary testicular failure. Okay, the other ones, are you all with me? What's wrong with him? Sertorial cell only syndrome? Uh-huh, so sertorial cell only, then as I said, that sertorial cell only syndrome will not impact testosterone and LH level. So yeah, I think Joseph is correct.

This is called testicular failure or primary hypogonadism. Okay, so the testis does not work. Because you have a low testosterone level, you lost the feedback.

You have a high LH level, high FSH level, and because you have an entire testicular failure, all cells dysfunction, so you do not make inhibitin B. Does the story make sense? Okay, another one, another guy showed up. Reduced testosterone, increased LH. FSH is either increased or not changed or normal.

Inhibitin B is normal. What's wrong with him? Some sort of late cell dysfunction. Uh-huh, okay.

Is Andrea and Alindro with me? What's wrong with him? His testosterone is low. His leading cell is not making testosterone, right? So testosterone is down. You lost the feedback.

You now have a LH. FSH is intact or increased, but inhibitin B is normal. So it has a perfectly functional sertoli cells.

So this guy has a leading cell failure. Okay, next one. Another guy showed up.

Testosterone is normal. LH is normal. FSH goes up.

Inhibitin B goes down. What's wrong with him? What went wrong? Something inhibitin B goes down means oops. Which cell doesn't work? That's the sertoli cell.

Perfect. Sertoli cell doesn't work. FSH goes up.

Testosterone and LH are intact. Yeah. What's that phenotype called? What's this disease called? Sertoli cell is there, but it's not working.

What is that disease again? Sertoli cell only syndrome. Okay. Again, this is the majority of the guy if he doesn't have tubal reasons.

So he showed up. He never do a varicose me and his tubules are intact. Urologists will mainly suspect he has a sertoli cell only syndrome.

Okay, last one. I've had one patient with that. Unfortunately, the microtest didn't work.

Oh yeah. You never know. Okay.

Last one. Someone showed up. Testosterone goes down.

LH goes down. FSH goes down. Inhibitin goes down.

Everything is down. What's his problem? I call it a secondary hypogonadism. You call it a secondary hypogonadism? Okay.

Which disease have we talked about in the lecture? This guy, I'm sorry? Kalman syndrome. Yes, that's exactly what's his problem. It's a Kalman syndrome.

And especially if he has another signature of this disease called a nose man. He doesn't smell anything. He has Kalman syndrome.

All right. So these are other quiz questions, but it's really, I don't want to take up too much of time. So I think that for that, I think everybody did a very great job.

I hope that I make this complicated scenarios as simple as I can. And of course, endocrinology is always confusing. A lot of even embryologists at the senior level still get confused though about the endocrine part of the reproduction.

If you have any question, you feel free to reach out to me. You can find me on LinkedIn or shoot me an email. It's my full name, at sutterhealth.org. Okay.

And I hope you enjoyed all the lectures today and everybody have a good night. Go eat some good dinner. It's too much for today.

Marina, do you have anything to say? I could not agree more. It's time for dinner. So go relax.

But I enjoyed, I personally enjoyed this two lectures so much. And I think it was very thorough and definitely at the level that we're trying to teach, which is graduate level clearly. And if you guys have any feedback at all to us, for us, we encourage you to be, don't be shy, you know, be direct.

We're all very direct in this group. So, you know, no offense will be taken, but the feedback will be taken into consideration. Any questions? No questions.

Andrea asked me through chat if it's possible to have this slides ahead of time from ASRM and I'm going to check into this and see if there is any policy about that. And we'll have an answer next Tuesday or sooner, if it's okay to distribute, we'll distribute sooner. Okay.

That's great. See you next week. Marina, hold on.

First of all, guys, great session. Thank you, Kelsey. Thank you, Yuning.

These were amazing lectures. Thank you so much and a lot. I loved the interactive questioning at the end and I loved the fun what's wrong with him scenario.

That's really fun. Everything? Yes. But yeah, you can expect the lectures will vary depending on our lecturers, but they'll be to this level.

And I think that we'll all get a lot out of it. Marina, you did mention you wanted to ask everybody about a screenshot. Yeah, I was planning to put a screenshot of today's lecture on social media and it actually shows everybody's names.

So I need your permission verbally. It's okay to put it on LinkedIn and maybe on the embryology group. So the time to speak is now.

Okay. All good. Okay.

Sounds good. Thank you, Stephanie. I almost forgot.

Okay. See you guys next week. Have a good week.

Have a good week. Bye, everyone.