Reproductive system

Hey everyone! It's Nicole from Kenhub, and in this tutorial, we'll be looking at the male and female reproductive systems. And the main images that we're going to be looking at today are, of course, our anatomical male and our anatomical female. And in this tutorial, we're going to be talking through both the internal and external structures of the male and female reproductive systems but let's first begin with the male reproductive system.

The male reproductive system has several functions including the production of gametes for the fertilization of the female's ovum as well as the nourishment of the developing fetus. And, of course, within the male reproductive system, we'll begin looking at the internal structures. And these include the testes, the vas deferens, the seminal vesicle, the ejaculatory duct, the prostate, the bulbourethral gland and the urethra. Let's, of course, begin with the testes.

So on our image on the right, you can see the testes highlighted in green and the testes are the primary male reproductive organs as they're responsible for the production of sperm and testosterone. And as you can see in the image, they are oval-shaped or egg-like in shape and they contain seminiferous tubules within their lobules – and I've drawn in the seminiferous tubules in their coils for you in dark gray. The seminiferous tubules make up the majority of the contents of the testes and are thin-coiled tubules that double up on one another and the seminiferous tubules are the site of spermatogenesis.

The testes are covered with a visceral layer of tunica vaginalis which is a remnant of a pouch of peritoneum – and you can see it drawn in blue in this image – and attached to the posterior pole of each testicle is a firm, highly coiled tube known as the epididymis as the site of maturation and storage of spermatozoa – and you can see it marked in dark gray on our image. As you can see, it's also contained within the tunica vaginalis and it's continuous with the vas deferens which we'll talk about on the next slide. One thing I want to mention before we do move on though, it should be noted that the temperature within the body cavity is generally too high for normal spermatogenesis and that's why the testes and the epididymis are located outside of the abdominal cavity. The testes also lie within the scrotum which is an external sac made out of skin and you can see the scrotum highlighted in green.

As we mentioned earlier, the vas deferens, also known as the ductus deferens, is a blind tube and is also the continuation of the epididymis and if we look at our sagittal view of the male pelvis, we can see the testes here highlighted in blue with the epididymis highlighted on its posterior pole and the vas deferens in green coming off that and near the half of the vas deferens is the part that's highlighted in green that's attached to the seminal vesicle. And the vas deferens continues from the highlighted green down the bottom ascending posterior to the testes and medial to the epididymis, and the middle part of the vas deferens is obviously cut out in this image.

The vas deferens has a relatively thick muscular wall and a thin lumen and as you can see, it also forms the main component of the spermatic cord which is a structure made up of the ductus deferens and other vessels that passes through the inguinal ring and is visible here just through this blue ring. So if you remember our vas deferens as it arises from the epididymis, you can imagine it and the spermatic cord passing through the inguinal ring in blue to join the green portion of the vas deferens. I'm just going to bring in one more image for you here, this is a ventral image of the male pelvis with the vas deferens highlighted in green, and this also demonstrates the spermatic cord passing through the inguinal ring.

But coming back to our sagittal section, you can see the ampulla of the vas deferens which is an enlargement in its terminal end just before it joins with the duct of the seminal gland to form the ejaculatory duct, and the ampulla is just about here.

Let's now have a brief chat about a structure that is connected to the vas deferens and which we mentioned briefly before, and as the vas deferens ascends, it crosses the ureter traveling to the posterior aspect of the bladder where it joins with the seminal vesicle to form the ejaculatory duct. So, if you look at our image, we have the vas deferens which if you'll recall from our previous slide, joining with the green seminal vesicle. And the vas deferens actually travels medial to the seminal vesicle which I've dotted out in dark gray so you can sort of see it x-ray visioned through the seminal vesicle, and these two come together to form the ejaculatory duct which is located within the prostate – and I'm pointing the prostate out now with my arrow.

The seminal vesicles also known as the seminal glands are considered to be accessory glands of the male reproductive system and as you can see, they're obliquely shaped and do you remember that they do not store sperm. Instead, they secrete a fructose-rich alkaline fluid which the sperm use as an energy source and a coating agent that is mixed with sperm as it passes through the ejaculatory ducts. The secretions from the seminal vesicles makes up around about seventy percent of the volume of ejaculate.

Let's move on now to the ejaculatory duct and shortly after it formed from the union of the vas deferens and the seminal vesicle, the ejaculatory duct pierces and enters the prostate gland which we mentioned briefly before where it opens up into the prostatic part of the urethra. So, in this image, let's just center this image of the prostate and the urethra in coronal section and point out a few things while we're here. So, up the top, we have the prostate while down the bottom here, we have the penis and coming down the middle of the penis is the urethra which is the passageway through which sperm and urine pass, and zooming in to come a little bit closer to our ejaculatory ducts, you can see the ejaculatory ducts highlighted in green opening into the prostatic urethra to form a slit-like opening, and the prostatic part of the urethra is highlighted in green. And this little thing that we've highlighted here is the seminal colliculus, and the seminal colliculus is a small elevation at the opening of the ejaculatory ducts in the urethra.

Now moving back to our sagittal image of the male pelvis, you can see the prostate highlighted in green. And you can see here that it's a chestnut-sized gland and it sits at the neck of the bladder and surrounds the proximal portion of the urethra. In this coronal section, you can clearly see the prostate as it surrounds the proximal portion of the male urethra and you can see that it's sitting just below the neck of the bladder and is bordered inferiorly by two glands – the bulbourethral glands which are accessory glands of the male reproductive system and which we'll talk about a little bit more on the next slide.

The prostate gland is also an accessory organ of the male reproductive system and the secretions from this gland contained components that are important for active sperm motility and these secretions make up about thirty percent of the volume of ejaculate. And if you remember from a couple of slides back, we mentioned that the seminal vesicles secrete a fluid that makes up around about seventy percent of the volume of ejaculate. So, just remember that the other thirty percent is made up of secretions from the prostate. The prostate gland has no contact with the peritoneum as it lies in the extraperitoneal space of the male pelvis, however, it is surrounded by a firm connective tissue capsule known as the fibrous capsule of the prostate and we've highlighted it for you in blue.

Let's move on now to the bulbourethral glands which we mentioned briefly on the previous slide, and the bulbourethral glands which are also known as Cowper's glands, secrete a clear watery fluid that lubricates and repairs the urethra for the passage of sperm. They're embedded in the deep peroneal pouch and as you can see, these two glands are situated posterolateral to the intermediate part of the urethra and they open to the posterior aspect of this part of the urethra.

So, we've been talking a lot about the urethra in previous slides and now I want to take a few minutes to look a little bit deeper into the urethra. The male urethra is not only part of the urinary system evacuating urine from the bladder but it's also part of the reproductive system and it access a passageway for male ejaculate. The male urethra is comprised of four parts namely the preprostatic part which is the initial part of the urethra that starts just after the internal urethral orifice – and you can see that highlighted in green on the right; we also have the prostatic part which is the portion of the urethra that passes through the prostate gland – and that's now highlighted in green; the membranous part which connects the prostatic urethra to the spongy urethra; and finally, the spongy part which is also known as the penile urethra as this is the part of the urethra contained in the corpus spongiosum of the penis. And the spongy part of the urethra can be further subdivided into the bulbar urethra which is located in the bulb of the penis and which you can see in the section just here and the pendulous urethra which runs the length of the penis. The spongy part also opens to the outside through the external urethral orifice as you can see in this image just here.

So now that we're finished talking about the internal organs of the male reproductive system, let's now look at the external organs of the male reproductive system and there are only two components of the external male reproductive system – the penis and the scrotum. So we're going to begin, of course, with the penis, and the penis is highlighted here in green. And as you can see, it is the largest part of the external male reproductive organs and it's made up of three parts – the root of the penis, the body of the penis and the glans penis.

Let's, of course, begin with the root, and the root of the penis is, of course, the most medial part of the penis and it's comprised of the bulb of the penis and the crura of the penis which are lateral curvatures of the corpus cavernosum that attach to the ischiopubic ramus. The penis also has the body of the penis which is the majority of the penis and it's made up of three masses of erectile tissue – the paired corpus cavernosum and the corpus spongiosum. The third part of the penis is known as the glans penis and it's the most distal part of the corpus spongiosum and as you can see, it forms a bulbous shape. The glans penis is the part of the penis that is normally covered by the foreskin or the prepuce which is a double layer of skin and is also the connective tissue that extends from the neck of the glans to just beyond the tip of the penis, and you can see that highlighted in green on the right.

The other external organ of the male genitalia is the scrotum seen here highlighted in green and which we mentioned earlier in the tutorial. And the scrotum is a wrinkled sac comprised of skin externally and the superficial fascia of the abdominal wall internally and the scrotum houses the testes, the epididymis and the distal part of the spermatid cord.

So now that we've covered the organs of the male reproductive system, let's move on to talk about the organs of the female reproductive system. And the female reproductive system, like the male reproductive system, has several functions all of which contribute to the complex process of reproduction. And the functions of the female reproductive system include the production of gametes which otherwise known as eggs or ova, the production of female sex hormones – estrogen and progesterone, and the facilitation of the occurrence of reproduction. And like the male reproductive system, there are internal organs and external organs and, of course, like the male reproductive system, we're going to talk firstly about the internal organs.

And the internal organs consist of the ovaries, the fallopian tubes, the uterus and the vagina. And, of course, let's begin with the ovaries. As you can see in this image, the ovaries are highlighted in green, and the ovaries are not only the gonads of the female reproductive system but they're also endocrine glands that secrete female sex hormones. The ovaries are analogous to the testes in the male – and just to remind you, let's slip in our male with the testes highlighted in green on our right here while we just bump our anatomical lady over – and as you can see for both genders, the ovaries and the testes are both located in the region of the pelvic cavity.

So let's come back to our image of the anatomical female as we're done with the male for the moment, and moving onto a ventral image of the uterus and fallopian tubes within the pelvis, we can see the ovaries highlighted in green on either side of the uterus, and these oval-shaped organs are attached to the fallopian tubes at one extremity via the suspensory ligament of the ovary and you can see this more clearly in this image with the uterus pulled back. And just to point out a few things for you, the uterus is this structure just here in blue. The fallopian tubes are highlighted for you in blue as well, and the suspensory ligament is highlighted for you in blue. And, of course, the ovaries are responsible for producing female gametes or oocytes as well as the female sex hormones.

As we just saw in the previous slides, the fallopian tubes are closely related to the ovaries and they're important structures of the female reproductive system as they are involved in the transport of the ovum from when it is released from the ovaries to the body of the uterus. The fallopian tubes also produce a site for the fertilization of ovum and you may come across the fallopian tubes being referred to as uterine tubes or oviducts, but don’t be confused as they all mean the same thing.

Now, there are a few parts to the fallopian tubes and we're going to talk through them right now. Firstly, there's the intramural part which is located within the myometrium of the uterus. We also have the isthmus which is a lateral continuation of the intramural part and the muscular part of the fallopian tubes. We also have the ampulla which is the widest part of the fallopian tubes and the most common site of fertilization. And, finally, we have the infundibulum which is the distal end of the fallopian tubes and it opens up into the peritoneal cavity, and this funnel-shaped part of the fallopian tube has fingerlike mucosal projections at its distal end which you can see just here and these are known as fimbriae, and these fimbriae attach to the superior aspect of the ovaries.

Moving on now, I want to talk a little bit about the uterus. And the uterus is a hollow organ of the female reproductive system and it plays an important role in reproduction as this is where the implantation and nourishment of the fertilized ovum takes place. As you can see, it lies dorsocranially on the urinary bladder and is situated anterior to the rectum and in this sagittal section on the right of the pelvis from the lateral right view, you can, of course, see the uterus highlighted in green with the bladder sitting anterior to the uterus in blue. And you can also see the rectum which is now highlighted in blue and that's, of course, posterior to the uterus.

The uterus also has several parts and we're going to talk through them now. The uterus has a body which is also known as the corpus, and as you can see, it has a triangularly-shaped lumen through its connection to the isthmus and both the fallopian tubes. The isthmus of the uterus is a short narrow passage or constriction that connects the cervix to the body of the uterus. And, of course, we have the cervix which consists of a part projecting into the vagina but also has a supravaginal portion that is fixed in the parametrium. And as such, the cervix has two orifices – the internal orifice to the isthmus and the external orifice to the vagina. Both the body and the fundus of the uterus which is the base of the uterus are covered by a visceral peritoneum and this visceral peritoneum is reflected onto the bladder in the rectum to form what is called the vesicouterine pouch and the rectouterine pouch respectively.

A brief note over here, it's important to know the anatomical position of the uterus as this will be important in clinical situations. And the body of the uterus is bent forward against the cervix at the isthmus and this is known as anteflexion which you can see represented by the blue line. Also the long axis of the uterus is inclined towards the vagina and this is known as anteversion which you can see represented by the gray line. So having said that, please remember that the most common position of the uterus is anteflexed where the body of the uterus is flexed forward and anteverted where the cervix is angled forward.

Let's now move on to the vagina. And the vagina or the birth canal is a fibromuscular tube surrounded by pelvic connective tissue on all sides, and in this image, you can see the vagina highlighted in green inferior to the uterus which, if you recall in the structure, is just here in blue. And, of course, if we come back to our image of the vagina from the ventral view, we can see it highlighted in green with the uterus again here in blue.

The function of the vagina is to facilitate childbirth, menstruation and to act as the receptacle for the penis during sexual intercourse. The vagina is also one of the most expansile organs of the female body due to the extensive connective tissue space surrounding the vagina which contains an elaborate venous plexus around the vagina that results in the expansion of the vagina during childbirth.

One more structure that I want to mention is the Bartholin's glands. Now, these are two pea-sized glands situated at the opening of the vagina which are homologous with the bulbourethral glands in males. And in this coronal section of the female pelvis with the vagina highlighted in green with the uterus highlighted in blue, you can see the Bartholin's glands highlighted in blue down here. And these glands secrete mucus that lubricates the vagina.

Let's now move on to talk about the female external reproductive organs. And the organs we're going to talk about today include the vulval vestibule, the labia minora, the clitoris, the labia majora and the mons pubis. Of course, we're going to begin with the vulval vestibule. And the vulval vestibule is otherwise known as the external opening of the vagina and it's also sometimes known as the vulva. In some cases, the vulva may be partially covered by membrane formed by an inward folding of mucosa called the hymen.

The labia minora are two thin longitudinal folds devoid of fat that are usually enclosed between the labia majora by the pudendal cleft and you can see these highlighted in green. And these two folds enclose an area known as the vestibule which contains the vaginal and urinary openings along with the openings of the lesser and greater vestibular glands, and the vestibule is this section just here highlighted in blue while the urethral opening is just here and the vaginal opening is just here. And it's a little hard to tell in this image but the labia minora unite over the glans clitoris which we'll look at in the next slide to form a covering for the clitoris known as the clitoral prepuce or the clitoral hood which you can see in this circle just here.

Moving on now to talk about the clitoris, the glans clitoris more commonly known as the clitoris is the erectile tissue of the female reproductive system. And the glans clitoris has a pair of corpora cavernosa comprised of erectile tissue enclosed in dense fibrous tissue. The clitoris is analogous to the structure of the penis in males but it doesn't have any urinary function as it does not contain the urethra – as we mentioned before, the urethra is down here in the vestibule. The clitoris is richly supplied with autonomic efferent nerve endings and is highly sensitive to sexual stimulation.

Let's come back to our image of the inferior pelvis with the labia minora highlighted. And in this slide, we want to talk about the labia majora which we're dotting out in blue, and as I mentioned earlier, the labia minora are usually enclosed by the labia majora which are a pair of thick folds of skin and adipose tissue found inferior to the mons pubis. And if we just bring in this image of the female pelvis in coronal section, we can see the round ligament of the uterus passing through the inguinal canal and continuing into the labia majora, and the labia majora in this image are down here in these blue circles. The labia majora remained hairless until puberty hits after which their lateral surfaces are covered in pubic hair hence they form the lateral boundaries of the pudendal cleft.

And, finally, the last structure we want to talk about is the mons pubis which is a rounded eminence in front of the pubic symphysis that consists of a massive subcutaneous adipose tissue and after puberty, the mons pubis bears the most pubic hair.

So now that we're finished talking about the organs of the male and female reproductive systems, let's quickly go through our summary of what we've talked about today. So the male reproductive organs, we talked about the internal organs which include the testes which are the male gonads, the vas deferens which is a continuation of the epididymis, the seminal vesicle which supplies secretions which make up the ejaculate, the ejaculatory duct which pierces and enters the prostate gland, the prostate gland itself which is an accessory gland, the bulbourethral glands which also produce a part of the ejaculate, and the urethra which is the passage through which semen and urine pass.

And as we mentioned, the urethra has four parts – the preprostatic part which is the part before the prostate, the prostatic part which passes through the prostate, the membranous part which connects the prostatic part with the spongy part, and the spongy part which is named because of the spongiosum. And the spongy part can be divided into the bulbar urethra as well as the pendulous urethra.

We also looked at the external male reproductive organs which include the penis, the largest external organ which itself can be divided into the root which is made up the bulb and the crura, the body which is made up of the paired corpus cavernosum and the corpus spongiosum as well as the glans which is covered by a prepuce. We also talked about the scrotum which houses the testes, the epididymis and the distal part of the spermatic cord.

With regards to the female, we talked about the internal structures which included the ovaries which are the female gonads, the fallopian tubes which help transport the ovum from the ovaries to the uterus and the fallopian tubes, of course, can be divided into four parts – the intramural part which is located within the myometrium, the isthmus which is a lateral continuation of the intramural part, the ampulla which is the widest part of the fallopian tubes and the infundibulum which is the distal end of the fallopian tubes. And the infundibulum also give rise to the fimbriae.

We also looked at the uterus which is made up of a body, the isthmus of the uterus and the cervix part of which projects into the vagina, and, of course, we talked about the vagina which is a receptacle for the penis during sexual intercourse and is also the passageway for childbirth and menstruation.

With regards to the external organs, we looked at the vulval vestibule which is the external opening of the vagina, the labia minora which enclose an area known as the vestibule, the clitoris which is the sexual organ of the female, the labia majora which are a pair of thick folds of skin and finally, we looked at the mons pubis which is a rounded and massive subcutaneous adipose tissue in front of the pubic symphysis.

Hope you enjoyed this video. Thanks for watching!