An important part of understanding your fertility is understanding your anatomy and what parts play what role.
We have put together this simple guide covering all the essential parts of the male reproductive system hopefully in a simple and easy to understand way.
Internal and external
In contrast to the female reproductive system where the labia majora, labia minora, clitoris, vestibular bulbs, vulva vestibule, vaginal opening, and the urethra and are regarded as the external reproductive organs, the man’s external reproductive organs are the scrotum with the testicles, and the penis.
Penis
The penis has 3 main parts, the root, the body (shaft) and the glans (head). The root of the penis is attached to the wall of the abdomen. The shaft of the penis is made up of a spongy like, erectile tissue and contains three chambers, the two corpora cavernosa and the corpus spongiosum. During sexual arousal the corpora cavernosa fill with blood allowing the penis to become and stay erect. When a man has an erection, a sphincter muscle at the bladder neck closes the urethra making it impossible for a man to urinate. This muscle relaxes again some time after the ejaculation.
The urethra travels through the body of the penis with its outlet at the tip of the glans. In some men this can be off centre.
The glans (head) of the penis is where the urethra expels urine and semen. The glans is the area of the penis which has the most nerve endings and sensitivity making it important in sexual stimulation and ejaculation. Over sensitivity of this area is a possible cause of premature ejaculation.
Scrotum
The scrotum is a pouch like sack of skin outside of the body that houses the testicles, blood supply and nerves. It provides protection to the testicles and helps regulate testicular temperature. The testicles are outside the body to keep their temperature 2 – 3 degrees (Celsius) cooler than body temperature as this is the optimal temperature for sperm production.
The scrotal sack has muscles within its wall that allow it to contract and loosen to adjust to changes in temperature loosening the scrotum in heat and tightening it when cold.
Testicles
The testicles are oval shaped organs (approximately 4-5 cm long, 3 cm high, and 2.5 cm wide), are responsible for spermatogenesis and are the main site of testosterone production (apart from a very small amount produced in the adrenal glands). Each testicle, of which there should be 2, is held in place by the spermatic cord which also supplies blood to the testicles.
When boys are born, the testicles are in the lower abdomen and should move down naturally into the scrotum 3 to 6 months after birth. Delays in this process or delays in surgery to rectify the issue can be a common cause of fertility issues later in life.
Typically, men’s testicles are slightly different in size and one will hang lower than another. The average volume of a testicle will be around 12 – 20mL2 and testicular volume will contribute to a man’s sperm count and hormone balance. Smaller sized testicles can be a sign of testosterone deficiency. Within each testicle is a series of small tubes known as seminiferous tubules.
Seminiferous tubules
The seminiferous tubules house germ cells which develop into sperm in a process known as spermatogenesis. This process is supported by “nursing” cells, also called Sertoli cells, which are there to support the growth and development of sperm. Sertoli cells are also involved in the hormonal regulation of testosterone production. Men can have what is known as “Sertoli cell only syndrome” which means there are no germ cells present, so he will not be able to produce any sperm.
Other cells which are important in terms of testicular function and sperm development are the Leydig cells. These sit in a space between the seminiferous tubules and are responsible for producing androgen hormones including testosterone. Both, the Leydig and Sertoli cells respond to different hormones produced by the pituitary gland in the brain and help regulate sperm production.
Men who produce very little sperm may go on to have what is known as a MICRO TeSE (micro dissection testicular sperm extraction). This is a surgical procedure carried out under a high-powered microscope where a surgeon will attempt to locate sperm within the seminiferous tubules.
Epididymis
The epididymis is a long tube-like structure that sits on the back and side of each testicle. Its main function is the maturation, storage, and transportation of sperm. It is a tightly coiled tube approximately 6 to 7cm in length. However, if taken out and uncoiled it would stretch to approximately 6 m long.
The epididymis is made up of 3 main areas, the head, body and tail. The head receives the sperm from the testicle where they then travel into the epididymal body. The tail of the epididymis then merges into the vas deferens. This is also the place where sperm are stored until ejaculation.
It takes sperm approximately 2 to 6 days to travel through the epididymal body where they develop into fully motile sperm before being stored in the tail of the epididymis ahead of ejaculation. The whole process of epididymal sperm maturation takes about 12 to 14 days.
The epididymis also plays an important role in the protection of sperm as it produces a multitude of antioxidants to protect the sperm from oxidative stress during transit. The longer sperm are stored within the epididymis, the more prone they are to damage from oxidative stress which is why antioxidants are an important part of a man’s diet and why regular ejaculation is also important to eliminate old and damaged sperm.
Where a man is not ejaculating sperm due to a blockage or failed vasectomy reversal, a surgeon may carry out a MESA (microsurgical epididymal sperm aspiration) or PESA (percutaneous epididymal sperm aspiration) operation to attempt to extract sperm directly from the epididymis.
Vas deferens
The vas deferens are a long muscular tube that carry the sperm from the tail of the epididymis to the ejaculatory duct. The vas deferens travel from the testicles through the inguinal canal back into the body where they join the ejaculatory ducts. The vasa deferentes use peristaltic movement to transport and help expel sperm during ejaculation.
Ejaculatory duct
The ejaculatory ducts are a paired structure housed within the prostate which receive sperm from the vas deferens and fluid from the seminal vesicles. The vasa deferentes deliver the sperm from the epididymides into the ejaculatory ducts where they are then mixed with fluid from the seminal vesicle before moving through the prostate gland via the urethra.
Seminal vesicle
The seminal vesicles are a pair of tubular glands which sit between the bladder and the rectum. Their primary role is to provide nutrients to the sperm in the form of fructose and they provide around 60% of the fluid that later becomes semen. This fluid mixes with the sperm as they travel through the final stages of the vasa deferentes into the ejaculatory ducts and onto the urethra.
Prostate
The prostate is both a gland and a muscle and is an essential part of the male reproductive system whilst also controlling the mechanism of urination.
The prostate houses the ejaculatory ducts which receive sperm from the vasa deferentes and fluid from the seminal vesicles.
The prostate further adds an additional 30% to the seminal fluid by adding prostatic fluid giving semen it’s milky white colour whilst also making it more alkaline, ready for its journey through the female reproductive tract where the vaginal environment is predominantly acidic.
The prostate contains smooth muscle tissue and has elastic tissue surrounding it. This, along with the contraction of the Bulbospongiosus muscle (a muscle sitting at the base of the penis inside the body), helps in the process of ejaculation by squeezing the semen into and out of the urethra as part of its expulsion. The ejaculation occurs at an approximate speed of up to 45 km/h.
The prostate can become inflamed, known as prostatitis, due to infection or bacteria leading to urination and ejaculatory difficulties.
As men age, the prostate is increasing in size which can lead to problems with urination and potential urinary retention. This will need medical attention and potential surgery.
Prostate cancer is one of the most common cancers in older men which will cause symptoms similar to that of an inflamed prostate. Unfortunately, not all symptoms will be noticeable immediately. Therefore, as men age, regular blood tests for the prostate specific antigen (PSA) and prostate examinations are important and speaking to your GP if you have any concerns about your prostate sooner rather than later is incredibly important.
Urethra
The urethra is a fibrous muscular tube which travels from the bladder to the glans of the penis. The average male urethra is around 20cm’s long.
It is responsible for expelling urine from the bladder but also semen during ejaculation.
As the urethra passes through the prostate it has several openings to receive sperm from the ejaculatory duct and fluid from the seminal vesicle as well as prostatic fluid from the prostate itself.
During ejaculation several muscles work along with peristaltic contractions to force semen along the urethra and out the end of the penis.
Prior to ejaculation and during sexual stimulation several glands in the urethra work to produce a clear fluid known as pre-ejaculate (pre-cum) which cleans the urethra of urine. It is also thought that pre-ejaculate may help in lining the urethra to ease the passage of semen.
As the male urethra is much longer than the female urethra (only 3 – 4 cm) , men are not as prone to urinary tract infections (UTI’s). However, it is not impossible for men to suffer from these. This is also how sexually transmitted infections will enter the body. If untreated, these can travel to the testicles or the bladder and eventually the kidneys causing serious illness and potentially permanent damage.
Hormones
Hormones are an essential part of our health and when it comes to male fertility, they are crucial in sexual development, sex drive and sperm production.
As with all hormones in our body, it starts in the brain, namely the hypothalamus. This is ultimately the conductor for all hormone production.
The hypothalamus sends signals to the pituitary gland which releases hormones that are sent around the body. In the case of male fertility, the testicles receive these signals via receptors which in turn stimulate activity. As we saw earlier, there are 2 main cells involved in sperm and further hormone production these are the Sertoli and Leydig cells. Sertoli cells respond to follicle stimulating hormone (FSH) as a signal to “get to work” promoting the development of sperm. Leydig cells on the other hand respond to luteinising hormone (LH) to produce testosterone which helps with the maturation and development of sperm, amongst many other things, whilst also helping regulate hormone release from the pituitary gland.
There are several hormones that play a key role in male fertility and interestingly many of them are the same hormones that are present in women. They are:
- Testosterone (T)
- Dehydrotestosterone (DHT)
- Follicle Stimulating hormone (FSH)
- Luteinising hormone (LH)
- Oestrogen
- Prolactin
- Thyroid Stimulating hormone (TSH)
- Gonadotropin Releasing Hormone (GnRH)
- Inhibin B (a hormone produced by Sertoli cells)
Any imbalance within the hormonal system will negatively impact on sperm quality and quantity. A blood hormone test may also identify issues in any part of the hormonal system or testicular function.
There are many factors that can impact a man’s hormones including environmental or lifestyle-dependent exposure to endocrine disruptors (plasticizers etc.), stress, diet, exercise, medication and more.
For more in depth information on hormones check out our other article here.
Summary
In summary, the male reproductive system is a complex and finely balanced system. It will take approximately 60 – 65 days for germ cells to develop into fully formed sperm in the testicles with an additional 12 – 14 days for these sperm to mature and travel through the epididymis ready to be ejaculated. During this time, sperm will have already travelled many meters which, for the smallest cell in the body, is a very long way.
Any imbalance in any part of the male reproductive system is likely to have an impact on a man’s sperm quality and the function of those sperm. Both internal and external factors will influence fertility and sperm health and it is important that a man fully understands these. Taking the correct action around lifestyle and diet is paramount and thorough medical testing is equally important. This is why it is so important that men see the correct medical professional who will be able to assess all areas of a man’s health and truly understand where any issues may lie.