Testicle & Scrotum Anatomy
The two testicles are located inside a loose sac called the scrotum. The testicles have two main functions – first, to produce testosterone and second, to produce sperm. On the rear of each testicle is a coiled tube in a sac-like structure called the epididymis that stores sperm after it is produced in the testicles. The testicles are suspended by the spermatic cord which consists of blood vessels, nerves, and the vas deferens. The vas deferens delivers sperm from the epididymis to the other reproductive organs inside the body that make the fluids which will become semen.
The scrotum is a thin sac-like structure that protects and regulates the temperature of the testicles. The scrotum is made up of layers of skin, muscles, and fascia. Fascia is a term that refers to sheets of dense connective tissue. We’ve probably all seen examples of fascia when cutting meat. It is the tough, fiber-like material that connects to a muscle and separates it from another muscle. Each testicle is protected by multiple layers. The layers are as follows from the outside to the inside:
Dartos muscles and fascia
Cremaster muscles and fascia
Scrotal Skin (1st Scrotal Layer)
The skin of the scrotum is thin and wrinkly. Before puberty, the scrotal skin is the same color as the skin found elsewhere on the body. However, during puberty the scrotum will change color and become darker and thinner. The scrotal skin also contains blood vessels and nerves. One particular nerve, the posterior scrotal nerve, is worthy of note. Like the nerves on the penis, this nerve branches off of the pudendal nerve which provides and enhances sexual stimulation which can eventually lead to ejaculation.
Nearly all men will have hair on the scrotum. This hair is not as dense as other pubic hair. Some men only grow scrotal hair on the sides of the scrotum rather than in the center, while most men grow hair over the entire scrotum. Yet other men have hair covering the entire front of the scrotum while having bald patches on the rear of the scrotum. To learn more about scrotal hair click HERE.
Running down the center of the scrotum is a ridge of skin called the raphe. The raphe extends from the anus to the neck of the penis. The portion of the raphe on the scrotum is called the scrotal raphe. As we’ll discuss in just a moment, the raphe extends from the outer skin of the scrotum to deep inside the scrotum separating the two testicles into different sacs.
Dartos Muscles & Fascia (2nd Scrotal Layer)
The next layer in the scrotum consists of the dartos muscles and fascia. These lie directly below the scrotal skin. The involuntary contractions of the dartos muscles cause the wrinkled appearance of the scrotum. The dartos muscles line the entire surface of the scrotal skin and form two sacs – one on the right and one on the left. Having two sacs prevents the testicles from intertwining with one another. The left sac is almost always longer, causing the left testicle to hang lower in the scrotum. Beneath the dartos muscle is the dartos fascia. Fascia is a tough membrane like material that separates muscle layers (think of the tough membrane sometimes seen in steak).
Cremaster Muslces & Fascia (3rd Scrotal Layer)
The cremaster muscles lie just beneath the dartos layer. Instead of lining the entire sack, these muscles hug the testicle and spermatic cord tightly and are shaped like a tear drop.
When the cremaster muscles contract they pull the testicles tightly against the body causing the scrotum to tighten and pull into a smaller size and shape. When they relax, the scrotum relaxes and the testicles hang further away from the body.
The contraction and relaxation of the cremaster muscles serve two main purposes – protection and temperature regulation. First, let’s discuss protection. There are times that the testicles need to be pulled next to the body for protection. During sexual arousal and erections, the cremaster muscles contract. This pulls the testicles next to the body so they don’t dangle or get knocked around during intercourse. Second, the testes are located outside of the male body and in the scrotum because sperm can only develop properly at a temperature that is 2-4 degrees Fahrenheit (1-2 degrees Celsius) below body temperature. When the scrotum is exposed to temperatures cooler than ideal for the testicles, the cremaster muscles will contract, pulling the testicles close to the body to warm them up. Men often notice this “shrinkage” of the scrotum after swimming or being out in the cold. On the other hand, in hot weather or in a hot shower, the cremaster muscles will relax so the testicles can hang further away from the body and cool off. This contracting and relaxing of the cremaster muscles helps the scrotum maintain that 2-4 degree temperature difference that is necessary for sperm production.
The cremaster muscles work by reflex. Stroking the inner thigh can cause these muscles to contract by reflex, as seen in the illustration below. Clinicians often use this reflex to diagnose certain disorders that occur when there is scrotal pain or swelling.
Attached to the cremaster muscle is the cremasteric fascia. This fascia is connected to part of the internal oblique muscles in the lower abs, which accounts for some of the movement of the scrotum when the abdominal muscles are engaged and why disorders of the lower abdominal muscles can affect the scrotum.
Tunica Vaginalis (4th Scrotum Layer)
The final layer of the scrotum is a membrane called the tunica vaginalis. The tunica vaginalis lines the entire interior of the scrotum and creates a smooth surface for the testicles to move around in.
TESTICLES & EPIDIDYMIS
The testicles are oval in shape. They are firm but not hard. Each testicle is wrapped in two layers of protective, fibrous tissue. The inner layer is a tough layer called the tunica albuginea which protects the testicle. The second layer of tissue, called the tunica vaginalis, is the same layer that lines the scrotum. This allows the testicle to move freely inside the scrotal sac without much friction. In addition, the tunica vaginalis of the testicle is anchored in place to the scrotum by the scrotal ligament, which helps prevent the testicle from spinning and twisting. This ligament is what remains of the gubernaculum, a structure during fetal development that draws the testicles from inside the body cavity down into the scrotum prior to birth. For information on testicles that remain in or are drawn back up into the body rather than staying in the scrotum, click HERE.
The adult size of the testicles normally ranges from the size of a large grape to the size of an unshelled pecan – from about 1¼ inches (3cm) or 18ml to 2 inches (5cm) in height and ¾ inch (2cm) to 1¼ inches (3cm) in width or 26ml (see below). This can vary from individual to individual, and some men may notice that one testicle is slightly larger than their other testicle.[i]
The testicle has two main functions – to produce testosterone and sperm. The testicle is made up of small lobes filled with tightly packed tubules (tubes).
In between the tubules are connective tissues and blood vessels. This connective tissue contains Leydig cells which line the tubules and produce testosterone. The blood vessels carry testosterone to the rest of the body.
The coiled tubes are called seminiferous tubules. These tubules contain spermatocytes which develop into hundreds of millions of sperm each day. The spermatocytes are surrounded by Sertoli cells which give support and nutrition to the developing sperm. Sperm is then carried in the seminiferous tubules to the back of the testicle and enter the epididymis.
Sperm are the male gamete or reproductive cell. Men produce roughly 300 million sperm per day.[ii] That’s 12.5 million an hour or 200,000 per minute; that’s nearly 3,500 per second.
Sperm consist of three main portions – the head, middle piece, and tail. The head is filled almost entirely by the nucleus, which contains the chromosomes that will combine with chromosomes from the mother to begin a new life. At the tip of the sperm, surrounding most of the head, is the acrosome. The acrosome contains enzymes that allow a sperm to penetrate through the cell membrane of an egg. At the rear of the head is the centriole. From the centriole, spindle fibers extend all the way through the tail. The middle piece is packed with mitrochondria which are responsible for the energy needed for the sperm to swim. The tail allows the sperm to swim from the vagina to the fallopian tubes for fertilization.[ii] Abnormalities with sperm and sperm count will be discussed more in the section on infertility.
The epididymis is a comma-shaped structure that sits on the top and rear of the testicle. When a man feels his testicle, he will notice a soft structure at the back of the testicle – this is the epididymis. The portion of the epididymis that sits on top of the testicle is called the head of the epididymis – this is where the tubules from the testicle enter the epididymis. The portion along the back of the testicle is called the body of the epididymis. Here the tubules come together to form a single tube that is over 20 feet (7 meters) long. The part of the testicle that wraps just beneath the testicle is called the tail of the epididymis. This is where the tubule turns from descending downward and starts ascending upward and exits the epididymis.
Prior to entering the epididymis, sperm are considered immature as they cannot move or “swim” and they are unable to fertilize an egg. The function of the epididymis is to prepare sperm for fertilization. In the epididymis, the sperm “mature” so they are capable of fertilization (although they still are not able to swim). It is also in the epididymis that many damaged sperm are recycled and removed from the tubule. Finally, fluid is removed from around the sperm, thus creating a super concentration and compaction of sperm as they leave the epididymis. It takes approximately two weeks for sperm to complete their passage through the tubule in the epididymis and enter the vas deferens.
The vas deferens (sometimes called the ductus deferens) is a tube that connects the testicles/epididymis to the glands that produce sexual fluid inside the male pelvis. As the vas deferens leaves the tail of the epididymis, it travels up through the spermatic cord then up and over the bladder to a swelling called the ampulla. The two ampullas (one from each testicle) sit outside the rear base of the bladder next to the prostate and seminal vesicles. The total length of the vas deferens is around 16-18 inches (40-45cm).
The spermatic cord is made up of blood vessels, nerves, lymph vessels, the vas deferens, as well as connective tissues that include an extension of the tunica vaginalis that lines the outside of the testicle and inside of the scrotum (see image on previous page). These structures create a cord (hence the name spermatic cord) that runs from the testicle up to the lower abdomen. The blood vessels supply the testicle and the cremaster muscles with blood. These blood vessels form a plexus, or net of vessels, which acts to cool the blood and helps the testicles remain those 2-4 degrees below body temperature. The nerves running through the spermatic cord account for the sensitivity of the testicles and also assist the cremaster muscles. Lymphatic vessels serve to drain the area of excess fluid.
Men should do a testicular and scrotal exam monthly. The goal of these exams is to help a man identify any abnormalities that may indicate a problem, such as testicular cancer. Abnormalities may be difficult to spot if exams are not performed regularly. For a detailed explanation of how to perform a self-exam, click HERE.
In addition to doing a monthly self-exam, every man should have a testicular exam performed by a physician each year during an annual physical. A testicular exam is a normal part of a physical exam: so, if your healthcare provider does not perform a testicular exam during a physical examination, don’t be afraid to ask him or her to complete one.
Disorders of the scrotum and testicles
Abnormalities can be discovered during a testicular self-exam and may indicate a disorder of either the scrotum or the testicles. To learn more about disorders of the testicles and scrotum clicke HERE.
[ii] Tortora GJ, Nielsen MT, Principles of Human Anatomy, 13th Edition, 2014, p.833.
Images on this page from top to bottom include:
Claudio Divizia/Shutterstock.com &Pykodelbi/Shutterstock.com