视频：Male reproductive system

Throw down the ball. Yeah, go on. Don't worry. Just throw it. Ooh…ouch!

Male anatomy has always been a sensitive subject not just on the playing field but also in anatomy class. Grab yourself a cup of coffee and stay tuned as we learn about the male reproductive system.

In today's tutorial, we are going to learn all about the male reproductive organs which are divided into two groups –the internal and the external reproductive organs. Along the way, we will discover the functions of each organ and the functions of the male reproductive system as a whole. To finish off today's tutorial, we will also take a look at a clinical scenario to help apply and consolidate our knowledge. So without further ado, let's begin.

Before we dive straight in, let's take a quick look at the main functions of the male reproductive system. As a whole, the male reproductive system has multiple functions including the production, storage, and transfer of gametes, otherwise known as sperm, along with hormone secretion and sexual pleasure.

As previously mentioned, the male reproductive organs can be divided into internal and external organs. We're going to explore each of these groups individually, but first, let's just get a sneak preview.

Starting with the internal organs, this group consists of the testes, epididymis, spermatic cord, ductus deferens, ejaculatory duct, and several accessory glands including the seminal glands, the prostate gland, and the bulbourethral glands. Next, the external organs include the penis and the scrotum. Alright, are you ready to get down to the nitty-gritty? Great! Let's begin with the internal reproductive organs.

The testes, singularly known as a testis, are the primary male reproductive organs. These two oval-shaped structures reside in the scrotum and are responsible for the production of sperm and testosterone. The testes contain lobules that are primarily composed of seminiferous tubules separated by fibrous interlobular septa. Each septa extends from the mediastinum of the testis to the innermost layer of the external covering of the testes, the tunica albuginea.

The seminiferous tubules are thin-coiled tubes entwined with one another and are the site of spermatogenesis. Notably, the testes are located external to the abdominal cavity and within the scrotum as the normal internal body temperature is too high for spermatogenesis to occur normally.

Located within the mediastinum of the testis is another delicate tubule network known as the rete testis. The rete testis functions to transport sperm from the seminiferous tubules to the efferent ductules which we'll meet in a few minutes. Surrounding this network of tubules and septa is a tough fibrous capsule known as the tunica albuginea. The tunica albuginea together with the interlobular septa forms the connective tissue framework of the testis.

Superficial to the tunica albuginea is a layer known as the tunica vaginalis. The tunica vaginalis is a closed peritoneal sac composed of two layers – an inner visceral and an outer parietal layer. The visceral layer of tunica vaginalis lies on the external surface of the testes just superficial to the tunica albuginea. It surrounds the surface of the testis except at the attachment point of the epididymis and spermatic cord which we'll learn about shortly.

The parietal layer of the tunica vaginalis is the most external layer of tunica vaginalis. It is looser and extends in a superior direction creating a cavity between the visceral and parietal layers. The fluid within the cavity of the tunica vaginalis allows the testis to move freely within the scrotum. The tunica vaginalis also extends to encase the other internal reproductive organs that we will discuss next.

Within the scrotum external to the testes and surrounding the tunica vaginalis are three more fascial coverings. These coverings are extensions of the anterior abdominal wall which surround and extend along the spermatic cord to encapsulate the testes. The external coverings of the testes from deep to superficial include the internal spermatic fascia, the cremasteric fascia and muscle, and external spermatic fascia.

Attached to the posterior surface of each testis outside the tunica albuginea and contained within the tunica vaginalis is the epididymis. This firm and highly coiled tube consists of a series of ducts and is the site of spermatozoa maturation and storage. Straight efferent ductules extend from the rete testis to transport sperm to the epididymis. The epididymis is divided into three parts – the head, the body, and the tail which is continuous with our next structure, the ductus deferens.

The ductus deferens, also known as the vas deferens, is a long tube with a thick muscular wall and relatively thin lumen. The ductus deferens is a continuation of the tail of the epididymis. From here it transports sperm through the inguinal canal within the spermatic cord and into the pelvic cavity.

Let's briefly pause here to talk about the spermatic cord. This tubular structure suspends each testis in the scrotum. This cord traverses the abdominal wall by passing through the inguinal canal on its way to and from the testis and primarily contains the ductus deferens along with the associated neurovasculature. As previously mentioned, the spermatic cord is surrounded by extensions of the anterior abdominal wall which include the internal spermatic fascia, cremasteric fascia and muscle, and external spermatic fascia which also extend over the scrotum. As the ductus deferens travels through the inguinal region and into the pelvis, it courses alongside the bladder and medial to the ureter.

The final part of the ductus deferens is better examined from a posterior perspective. In this image, we can see the bladder and the ductus deferens passing medial to the ureter before enlarging to form the ampulla of the ductus deferens. It then terminates by joining the duct of the seminal gland to form the ejaculatory duct.

Before we move on, you may have heard of a vasectomy procedure that sterilizes males. This involves cutting and removing part of the ductus deferens, tying off both ends, and often culminates in recovering on the couch with a frozen bag of peas.

Cracking on, we have the first of the three accessory glands in the male internal reproductive organs. The two seminal glands, otherwise known as the seminal vesicles, are elongated, obliquely-orientated structures located between the bladder and the rectum. Importantly, the seminal vesicles do not store sperm. Rather, they secrete seminal fluid, a fructose-rich alkaline fluid that mixes with the sperm as they pass through the ejaculatory ducts. This fluid provides sperm with energy source and coating agent to neutralize the acidity of the vagina and cervical mucus. These secretions from the seminal vesicles comprise the bulk of the semen making up around 70 percent of the volume of ejaculate.

We've now reached the ejaculatory duct, which is a paired structure formed by the union of the ductus deferens and the seminal gland on each side. Shortly after this union, these ducts pierce and pass through the prostate and empty into the prostatic part of the urethra.

Now taking a central view and looking at this coronal section, let's take a moment to point out the anatomy. We have the prostate gland located below the bladder and the penis. We can see the urethra running through these structures. Zooming in, we can clearly see the slit-like openings of the ejaculatory ducts which empty into the prostatic part of the urethra.

Transitioning back to a sagittal view, we encounter our second accessory gland, the prostate gland. This chestnut-sized gland sits at the neck of the bladder and surrounds the proximal portion of the urethra, as you can see in this coronal section. The prostate gland produces and secretes a milky fluid that aids in the motility and activation of sperm. This prostatic secretion comprises the remaining 30 percent of the volume of ejaculate while as you may recall from a couple slides back, the seminal vesicles provide about 70 percent of the ejaculate’s volume. Note that spermatozoa make up a marginal percentage of the total volume of semen. Taking an even closer look at the prostate, you will be able to appreciate the fibrous connective tissue capsule surrounding this gland which contains its blood vessels and nerves.

Moving on to the prostate's inferior neighbor, we find the third and final pair of accessory glands – the bulbourethral glands, also known as the Cowper’s glands. These pea-sized glands secrete a clear watery fluid that lubricates the urethra in preparation for the passage of semen. From this sagittal view, we can see the bulbourethral glands located just inferior to the prostate and posterolateral to the intermediate part of the urethra. The bulbourethral glands empty into the posterior aspect of the urethra at this point.

Since we've mentioned the urethra quite a bit up to this point, let's take a few minutes to dive deeper into this structure. The male urethra is a muscular tube that is both part of the urinary system by evacuating urine from the bladder and the reproductive system as a passageway for male ejaculate.

The male urethra which we can see in this coronal section is comprised of four parts. The preprostatic urethra or intramural part is the initial part of the urethra that starts just after the internal urethral orifice. Next we have the prostatic urethra which is the portion of the urethra that passes through the prostate gland. Continuing on, there's the membranous urethra or intermediate part which connects the prostatic urethra to the spongy urethra. And finally, the spongy part, which is also known as the penile urethra. This is the part of the urethra contained in the corpus spongiosum erectile tissue of the penis that opens to the outside through the external urethral orifice.

With the internal organs all wrapped up, let's now turn our attention to the external reproductive organs.

Let's begin with the male copulatory organ – the penis. This organ's functions are reproduction by serving to introduce sperm into the female reproductive system during intercourse, sexual pleasure, and micturition since it conveys the urine away from the urinary bladder to the external urethral orifice to be expelled from the body. The penis is made up of three parts – the root, the body, and the glans penis.

In this inferior view, we can examine the root of the penis which consists of the bulb as well as the crura of the penis. The root of the penis is formed by the proximal expansions of two kinds of erectile tissues – the corpus spongiosum and corpora cavernosa. The bulb of the penis is formed by the proximal expansions of corpus spongiosum while the crura of the penis are formed by the paired corpora cavernosa. Here we can see these structures in a coronal view with the bulb and crura of the penis highlighted in green. Returning to our inferior view, the body of the penis makes up the majority of the organ and is similarly composed of three masses of erectile tissue – the paired corpora cavernosa and the corpus spongiosum.

Finally, the third part of the penis is known as the glans penis. This enlarged bulb-shaped tip is the most distal part of the corpus spongiosum. The glans penis is also covered by the foreskin, also known as the prepuce. Circumcision is removal of the foreskin so circumcised males have no covering over the glands.

At last we have reached the other external organ of the male genitalia which we've mentioned several times now – the scrotum. This wrinkled sac is covered externally with thin pigmented skin. The dartos muscle and fascia which are an extension of the superficial fascia of the abdomen make up the next layer. Internally, the scrotum is composed of the same layers of the spermatic cord. The scrotum houses the testes, epididymis, and the distal part of the spermatic cord including the ductus deferens.

So now that we've learned all about the male reproductive system, let's have a ball with a clinical scenario.

Perhaps you've heard of the medication Viagra or you've seen a T.V. commercial pertaining to males having difficulty achieving erections. In any case, erectile dysfunction is a common condition that impact most individuals with male anatomy transiently at some point particularly those who are elderly. That said, it is by no means non-existent in younger individuals and is probably under-reported.

The failure to achieve erection spontaneously or with adequate stimulation is the definition of erectile dysfunction. Given the mechanism of erection is actually very complex, the cause of erectile dysfunction is multifactorial. Some common causes, however, are arterial insufficiency that itself can manifest from many different medical conditions, psychogenic disturbance, and prior surgeries, namely, prostate removal which is also known as a prostatectomy.

Now what can be done for this problem? Consulting a doctor or urologist is recommended. Treatment will depend on the cause but some treatments include psychological therapies, encouraging communication, oral medications such as sildenafil, the active ingredient in Viagra, supplementation for low testosterone, vacuum erection devices, self-penile injections into the body of the penis, or penile implants.

Go ahead and give yourself a pat on the back as you've mastered the male reproductive system. Before you move on to the next tutorial, let's quickly summarize everything that we've learnt today.

We first covered the internal organs of the male reproductive system starting with the testes which are the male gonads responsible for producing sperm and testosterone. Next we looked at the epididymis where sperm is stored and matures. Then we talked about its continuation, the ductus deferens. Moving on, we discussed the spermatic chord specifically how it contains the ductus deferens and travels through the inguinal canal.

Now into the pelvic cavity, we looked at the first pair of accessory glands – the seminal vesicles – which supply secretions making up most of the ejaculate. Then we talked about how the ductus deferens and seminal vesicles unite to form the ejaculatory duct which pierces and enters the second accessory gland we discussed – the prostate gland. We subsequently covered the bulbourethral glands which produce a lubricating fluid as part of the ejaculate.

Rounding up the internal organs we looked at the urethra which is a passageway through which semen and urine pass. We also mentioned its four parts – the preprostatic part, the prostatic part, the membranous part, and the spongy part.

Continuing on, we explored the external male reproductive organs beginning with the largest component – the penis. We reviewed how the penis can be divided into the root which is made up of the bulb and the crura, the body which is made up of the paired corpus cavernosum and the corpus spongiosum, as well as the glands which is covered by the prepuce or foreskin.

Finally, we looked at the scrotum which houses the testes, epididymis, and the distal part of the spermatic cord. To conclude our tutorial, we looked at the clinical condition known as erectile dysfunction. Specifically, we discussed how this inability to achieve an erection is caused primarily by arterial insufficiency to the penis, psychogenic disturbance, and prostatectomy.

And that's it! See you next time and happy studying!