Video: Scrotum and spermatic cord
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The testes – the most precious crown jewels of male anatomy, hanging there in all of their glory. Unfortunately, however, that very dangling nature can get them caught up in rather uncomfortable an... Read more
The testes – the most precious crown jewels of male anatomy, hanging there in all of their glory. Unfortunately, however, that very dangling nature can get them caught up in rather uncomfortable and sometimes painful situations. So if they're so important, why are they hanging around in the first place? Why not tuck them away internally keeping them safe from external knocks and bumps? Well, like everything in anatomy, form follows function. Let's find out why as we explore the scrotum and the spermatic cord.
So let's not waste a moment and outline exactly what we will be exploring in this tutorial. We'll begin by reminding ourselves of the general anatomy of the scrotum and its number one occupant, the testis. We'll then take a closer look at the many layers of the scrotum learning about their origins and functions. After that, we will look at the contents of the spermatic cord which is effectively the anatomical highway between the trunk and the testis. Right, let's get started beginning with the structure and function of the scrotum and the testis.
Okay, so we all know that the testes are a pair of primary sex organs of the male and are located in the subpubic region of the pelvis along with the rest of the male reproductive components. The testes are ovoid-shaped bilateral organs roughly four centimeters long with a diameter of three centimeters in an adult male. They have two functional roles of sperm production and testosterone secretion.
The testes reside inside the scrotum – a double-chambered, fibromuscular cutaneous sac – which is suspended outside of the body. In addition to the testes, it also contains the epididymides and the distal part of the spermatic cord. It is an extension of the perineum and is located between the penis and the anus.
The scrotum receives its arterial blood from the posterior scrotal branches of the perineal artery, the anterior scrotal branches of the superficial external pudendal artery, and the cremasteric artery which is a branch of the inferior epigastric artery. Venous blood is drained by corresponding scrotal veins of the arteries whilst lymph is drained mainly to the horizontal tract of the superficial inguinal nodes.
Now let's look at the innervation of the scrotum using this illustration. The anterior aspect is innervated by the anterior scrotal nerves which are branches of the ilioinguinal nerve. Anterolaterally, the scrotum receives its innervation from the genital branch of the genitofemoral nerve. The posterior innervation comes from the posterior scrotal branches which arise from the perineal nerve which itself is a branch of the pudendal nerve. The inferior part of the scrotum or the bottom of the sac is innervated by the perineal branches of the posterior femoral cutaneous nerve.
Nope, that's not a mistake. There are actually two nerves titled perineal just to make things a bit tougher. Just remember that one is called the perineal nerve proper and the others are called the perineal branches of the posterior femoral cutaneous nerve.
Lastly, the dartos fascia of the scrotal wall is innervated sympathetically by the genital branch of the genitofemoral nerve.
To get a good view of the structures within, we have removed a flap of skin extending from the pubic bone down to the base of the scrotum. In doing this, we can see that the testis is surrounded by more layers of tissue than your typical onion. But don't worry, it's not as complex as it looks. In total, there are seven layers – two of which are considered part of the scrotum and three of which are related to the spermatic cord, and finally, two related to the testis.
We will first discuss the two layers which make up the scrotum. The outermost layer is the scrotal skin. The scrotal skin is thin and typically appears rugose which is a fancy name for wrinkled. It has numerous sebaceous glands and generally has a darker pigmentation to surrounding skin. You may notice a midline perineal raphe, which arises from the fusion of the urogenital folds during development. This raphe originates from the anus, across the midline of the perineum, and continues onto the inferior surface of the penis.
Unlike other areas of the body, there is no layer of subcutaneous adipose tissue underneath the skin in the scrotum. You can see here that the subcutaneous fat stops where the scrotum begins. Why is this you ask? Well, you'll see later that fatty insulation is the last thing the testis want. So we can skip over any fat and jump right to the next layer, which is the dartos fascia of the scrotum.
This layer tightly adheres to the skin and consists of superficial fascia and smooth muscle called the dartos muscle. The dartos fascia connects the perineal raphe to the inferior surface of the base of the penis forming the scrotal septum. This septum separates the scrotum into two halves. Typically, the left hand of the scrotum will sit lower than the right because the spermatic cord is longer and this is to allow the testes to overlap somewhat lowering the risk of injury.
So now that we've covered the scrotum, we will return to discussing the five deeper layers which are related to the testes.
The next three layers are often grouped together. This is because they also surround the contents of the spermatic cord and have the same origin during development. You probably already know that the testes undergo a descent during development from being inside the abdominal cavity to being outside of the body. During their descent through the inguinal canal, they carry the layers of the abdominal wall with them forming the layers of the spermatic cord as we can see in this illustration. This means that the three layers of the lower abdominal wall are also represented in the spermatic cord and the coverings of the testis.
The outermost layer of the spermatic cord and last to be pushed through by the testis is derived from the aponeurosis of the external oblique muscle which creates the external spermatic fascia. This is a thin membranous layer which is separated from the dartos muscle by a loose areolar connective tissue.
The second layer of the spermatic cord is the cremaster muscle and fascia which is derived from when the testis pushed through the internal oblique muscle. The cremaster muscle is under autonomic control, but can be tested by stroking the medial aspect of the thigh and this is known as the cremaster reflex.
The first layer which the testis pushed through is the transversalis fascia which we can see here. This creates the innermost of the three layers of the spermatic chord and is called the internal spermatic fascia. These three fascial layers surrounds the testis and contains the spermatic cord as we shall cover later in the tutorial.
The five layers we've just discussed act to protect the contents of the scrotum. They also play an important role in heat regulation. For example, when warm, the dartos and the cremaster muscles will relax lowering the scrotum and testes away from the body and consequently lowering the temperature of the testes. The numerous sebaceous glands in the scrotal skin, the lack of subcutaneous fat, and the dense subcutaneous plexus of blood vessels also increase capacity for heat loss. Conversely, the dartos and the cremaster muscles will contract when exposed to cooler temperatures pulling the scrotum and testes closer to the body which in turn raises the temperature. Arteriovenous anastomoses in the scrotal skin will also constrict reducing blood flow and limiting heat loss.
But why are there such extensive mechanisms for controlling temperature? Don't worry, we'll get to that a little bit later in the tutorial.
First, let's look at the innermost layers which lie closest to the testis. These are the tunica vaginalis and the tunica albuginea of the testis. Tunica means clothing in Latin and is often used in anatomy to describe the layers which immediately surround an organ. The outermost tunica is the tunica vaginalis which consists of two layers called the visceral and parietal layers which can be a little bit confusing to picture. But if we look at this illustration, we can see that although it looks like there are two separate layers, in fact, both layers are continuous with each other.
The visceral layer is innermost and tightly adheres to the testis. The parietal layer is the outermost layer and is separated from the visceral layer by the cavity of the tunica vaginalis. This cavity is filled with fluid which is secreted by the serous membranes in both layers and functions to give cushioning to the testis.
The next layer, the tunica albuginea, is best viewed if we return to this lateral view of the testis. This is a thick collagen-rich layer which lies underneath the visceral layer of the tunica vaginalis. The collagen gives the testis a whitish color and provides strength. Unlike the tunica vaginalis, the tunica albuginea is not reflected onto the underlying epididymis.
To memorize the names and order of the layers of the scrotal wall, try using the mnemonic Some Don't Even Call It The Testis. The first letter of each word in our mnemonic stands for the first letter of each layer of the scrotal wall. So, Some Don't Even Call It The Testis stands for skin, dartos fascia, external spermatic fascia, cremaster muscle, internal spermatic fascia, tunica vaginalis, and the tunica albuginea. And that's it! Our easy-peasy scrotal layers’ mnemonic Some Don't Even Call It The Testis.
Now that we've looked at the layers of the scrotum, let's take a closer look at the structure and the contents of the spermatic cord. As with any organ, the contents of the scrotum, notably the testis, requires an adequate blood supply, innervation, and lymphatic drainage. The body can readily supply these structures; however, what complicates the situation is that all of these vessels enter and exit the scrotum via the inguinal canal – a tightly-packed pathway. The result of this is the spermatic cord – a highly organized structure – which starts at the deep inguinal ring over here lateral to the inferior epigastric vessels. The cord then passes through the inguinal canal and enters the scrotum via the superficial inguinal ring. It ends at the posterior border of the testis.
There are quite a few structures for us to learn here so let me first give you an overview. We have three arteries, two veins, and two nerves, and finally, two other structures. Let's quickly look at each of these in detail.
The ductus deferens is the continuation of the epididymal tail. It is roughly forty-five centimeters long and acts to carry sperm out of the scrotum and into the ejaculatory ducts. If we look at the testis in isolation, the ductus deferens starts off somewhat convoluted but then straightens as it ascends within the spermatic cord behind the testis. It exits the scrotum through the inguinal canal and then leaves the spermatic cord at the deep inguinal ring. Eventually, it will go on to join with the duct of the seminal vesicle to form the ejaculatory duct which opens into the urethra.
The testicular arteries are a bilateral pair of vascular structures that branch directly from the abdominal aorta reminding us of the abdominal origins of the testis. Both the left and right testicular arteries course laterally to the common and external iliac vessels. They only cross the external iliac vessels as they enter the inguinal canal and spermatic cord via the deep inguinal ring. Once in the scrotum, the testicular artery gives off branches to the epididymis before bifurcating into lateral and medial branches which supply the testis.
The artery to the ductus difference arises from either the superior or inferior vesical artery which is given off by the anterior division of the internal iliac artery. It accompanies the ductus deferens into the testis where it anastomosis with the testicular artery.
The cremasteric artery arises from the inferior epigastric artery, which is a branch of the external iliac artery. It too forms an anastomosis with the testicular artery as it passes through the spermatic cord. It supplies the layers of the spermatic cord, the skin of the scrotum, and of course, the cremaster muscle. Its accompanying vein is variably present and drains the same structures returning venous blood to the inferior epigastric vein.
A rich network of approximately ten interconnecting veins drains the testis and the epididymis before forming a venous plexus known as the pampiniform plexus around the testicular artery. As this collection of veins course through and leave the spermatic cord, they progressively merge to form a single testicular vein. The left testicular vein follows a course similar to its arterial counterpart before emptying into the left renal vein. However, on the right side, the right testicular vein directly drains the inferior vena cava.
The pampiniform plexus plays an important role in the testicular thermoregulatory system. Autonomic fibers to the testis descend through the spermatic cord alongside the testicular vessels. These are mostly postganglionic sympathetic fibers which mainly originate from the celiac or aorticorenal ganglia. The fibers of the testicular plexus also carry sensory innervation from the testis.
Lymph is drained from the testis and epididymis via lymph vessels which course alongside the testicular vessels in the spermatic cord. These vessels return lymph to the lumbar lymph nodes.
The final structure of the spermatic cord is not visible in our main illustration. So let's change to this one where we can see the genital branch of the genitofemoral nerve. This supplies sympathetic innervation motor fibers to the cremaster muscle and the dartos muscle and sensory fibers to the spermatic fasciae and tunica vaginalis of the testis. The nerve also provides cutaneous sensation to the superoanterior portion of the scrotum.
To memorize the names and order of the layers of the components of the spermatic cord, try using the mnemonic Papers Don't Contribute To A Good Tango Lesson. Once again, the first letter of each word in our mnemonic stands for the first letter of each structure in the spermatic cord. So, Papers Don't Contribute To A Good Tango Lesson stands for pampiniform plexus, ductus deferens, cremasteric artery and vein, testicular artery, artery to the ductus deferens, genital branch of the genitofemoral nerve, testicular plexus, and lymphatic vessels. Not so difficult after all. Just remember the mnemonic Papers Don't Contribute To A Good Tango Lesson.
To wrap it all up, remember that all of the structures in the spermatic cord are packed together within three fascial layers which we spoke about earlier – the external spermatic fascia, the cremasteric muscle, and the internal spermatic fascia.
And that brings us to the end of our anatomy tutorial for today, so let's finish up with some clinical notes.
So we just said that the function of the spermatic cord is to stop various neurovascular structures from getting tangled. Well, as with most things anatomy, there is an exception. You see, occasionally, the entire cord itself can twist on itself restricting blood flow to the testis. Testicular torsion is a spontaneous condition occurring most commonly just after birth and during puberty. It has an etiology of about one in fifteen thousand males under the age of twenty-five each year and presents sudden severe testicular pain.
The testis itself may be swollen and sitting higher in the scrotum due to subsequent shortening of the spermatic cord. Treatment involves physically untwisting the testis through the scrotum and in severe cases will require surgery whereby the scrotum is excised to gain immediate contact with the twisted cord. If corrected within six hours, the outlook is promising with no lasting conditions. However, any longer than this can result in infertility and eventual tissue necrosis.
And that's it! We're officially educated on the anatomy of the scrotum and the spermatic cord. Before I leave you, however, I'd like to quickly summarize the two main topics which we covered in this tutorial.
The first major point of interest for us was the layers of the scrotum and the testis which we learned with the handy mnemonic Some Don't Even Call It The Testis. These layers were the skin of the scrotum, the dartos muscle and fascia, the external spermatic fascia, the cremaster muscle, the internal spermatic fascia, the tunica vaginalis, and finally, the tunica albuginea.
We then turned our attention to the contents of the spermatic cord which again could conveniently be summed up with a handy mnemonic. This time we said that Papers Don't Contribute To A Good Tango Lesson. Broken down, this gave us the following structures – the pampiniform plexus, the ductus deferens, the cremasteric artery and vein, the testicular artery, the artery to the ductus deferens, the genital branch of the genitofemoral nerve, the testicular plexus, and finally, the lymphatic vessels of the testis.
And there we are, done and dusted. I hope you found this tutorial helpful and don't forget to test your knowledge with our dedicated quiz on this video and our atlas page. Happy studying!