Homer Simpson’s Guide to The Male Reproductive System

The Male reproductive system has four regions – gonads duct system, accessory glands and the penis. The gonads are the testes, this is the site for sperm formation (spermatogenesis). The testis is located outside the body in the scrotum.

Embryological the testes develop within the abdomen and usually descend about seven months during the foetal development and if they do not descend a condition called cryptorchidism develops.

After decent the testes are located outside the body, giving a temperature 2-3 degrees Celsius cooler than the body temperature, which is the best temperature for the formation of sperms. If The testicles do not descend particularly before puberty, the spermatogonia are destroyed by the high body temperature and sterility results. Testicles that have not descended can be corrected either surgically or by hormonal therapy, but can also happen spontaneously.

The testis is variable in size, but the average size is about 5cm long and 2.5 cm in diameter. The testis is surrounded by a thick layer of connective tissue called the Tunica albuginea, which is thicker on the posterior surface of the testis, forming the mediastinum testis.


Clinical note: Testicular torsion. Testicular torsion is when the testis spins on its axis due to the dunes surrounding it. And as it moves it cuts off blood supply passing through the spermatic cord, causing ischaemia, extreme pain and ist not treated, necrosis of the testicular tissue. 

Varicocoele: this is the varicose veins develop in the blood supply to the testis and is seen in 8% of the normal males. 98% of the cases are on the left side due to mechanical damage to the left vein. 

Orchitis: this is when the testis become inflamed, with one or both being affected, orchitis is usually caused by the mumps virus. Symptoms include selling, tenderness accompanied by fever and caused result in sterility when mumps infection is involved.

From the mediastinum testis, connective tissue septa penetrate into the glands dividing them into 250 compartments called testicular lobules. Each lobule contains between 1 and four seminiferous tubules, which are supported by loose connective tissue that is rich in blood vessels and nerves. It is the seminiferous tubules where spermatogenesis happens.

The highly convoluted tubules are lined by a complex germinal epithelial layer, with tubules being 150-70 micro-meter in diameters and 30-70cm long. Where the tubules terminate they become cuboidal cells having a flagellum.  These terminal regions are called tubuculi recti.

The straight tubules connect the seminiferous tubules to a labyrinth-like series of channels called the rete testis, which is found in the mediastinum. The rete testis is then connected to the epididymis by 10-20 ducts called the efferent ducts.

The seminiferous tubules-  around the outside of each lobule is a layer of fibrous connective tissue that is lined by a basement membrane. This layer is called the tunica propria and within this layer next to the basement membrane are flattened myoid cells.

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The myoid cells act like smooth muscle and squeeze the tubules, pushing the non- motile spermatozoa towards the epididymis. The epithelium of the tubules is complex and consists of Sertoli cells and spermatogenic cells.

Sertoli cells are elongated pyramidal cells that form a sheath surrounding the lumen of the tubule and act to mediate nutrient and metabolic supply to the developing sperms.  In this way they also protect the developing sperm, from immunological attacks, this is because the immune system has developed long before sperm production begins and would recognise the sperms as foreign.

The Sertoli cells also secrete fluid into the tubules that move in the direction of the ducts, helping the sperm transport, and finally, the help concentrate testosterone into the seminiferous tubules which helps spermatogenesis.

The other cells that are found in the seminiferous tubules are the spermatogonia ( 46 chromosomes) which under mitosis to form primary spermatocytes. Spermatocytes under meiosis I to form secondary spermatocytes ( 23 chromosomes), which then undergoes meiosis II to form spermatids ( 23 chromosomes). Spermatids then mature to form spermatozoa.

Around the seminiferous tubules is interstitial connective tissue which contains nerves and blood vessels, as well as one important cells type, the Leydig cells that produce testosterone.

There are many different types of cells in the epididymis each having different functions involved in the maturation of sperms. The epithelium is involved in regulating the reabsorption and secretion of fluid, ions organic molecules and proteins into and out of the lumen as the sperms mature.

Clinical note: Epididymitis ( inflammation of the epididymis) is caused by prostatitis, UTI’s, mumps and STI’s. Usually, the only side is affected, with the epididymis swelling and becoming hard and excruciatingly painful. Epididymis can lead to sterility if not treated fast and efficiently; this is because the epididymis is the site for sperm maturation. Treatment is generally with antibiotics.  

The human sperm

  • The volume of ejaculate is between 3 and 5mls with the PH between 7.3 and 7.5
    Normal sperm count is about 75 million per ejaculate with lower numbers being 15 million. of the normal sperms, less than 20% should be abnormal
  • Of the possible approximately 400 million in an average ejaculate, only around 200 actually rich the oocyte( egg)
  • The prostate is a collection of 30-50 branched tubuloalveolar glands, the gland as a whole is surrounded by fibroelastic connective tissue sends the septa into the gland. The epithelium is usually columnar but can be cuboidal or squamous in places.
  • The prostate contributes to 20-30% of semen volume. components are fibrinolysin and fibrinogenase and buffers ( phosphate and bicarbonate buffers)

Clinical note: Prostatitis or inflammation of the prostate is seen in men above the age 50. Prostatitis is of unknown origin; theories suggest it may be as result of infection (UTI or STI)

From Erection and Ejaculation 

To enter the vagina the penis has to be erected. Erection can be brought about by psychic or tactile means. The most important stimuli for an erection to happen is touch; The glans penis is the most sensitive part of the penis because of it rich sensory and nerve supply.

Erection is caused by the parasympathetic nerve impulses from the sacral region of the spinal cord passing the penis, dilating the arteries of the penis. This causes blood, under high pressure to enter the blood sinuses of the corpus cavernosum and spongiosum of the penis.  This large quantity of blood compresses the veins leaving the penis so that most of the blood that enters stays.

As a result of this, the penis becomes engorged with blood and increases in both diameter and length. While the penis is becoming erect, the parasympathetic impulses cause the bulbourethral glands to secrete mucus that flows through the urethra to aid lubrication for intercourse. It should be pointed out that most of the lubrication comes from the female.

Once erection has happened, the next step is getting the sperm into the female reproductive tract. Once the sexual stimulus has become highly intense, reflex centres in the spinal cord carry sympathetic impulses that leave the spinal cord at the first and second lumbar vertebrae and pass to the genitals to begin emission.

Sexual stimulation causes nitric oxide to be released into the penis. This causes increased production of guanosine monophosphate, which relaxes the smooth muscle of the blood vessels of corpora cavernosa ( muscle found in the penis), allowing them to engorged with blood. Usually, following ejaculation, the enzyme phosphodiesterase 5(PDE5) removes GMP.

Viagra was discovered initially meant for treatment of cardiac issues. However, patient on viagra started reporting unusual side effects. Viagra works by inhibiting PDE5, thereby maintaining the erection.

Key Points

  • The Male reproductive system has four regions – gonads duct system, accessory glands and the penis. The gonads are the testes this is the site for sperm formation (spermatogenesis)
  • Embryologically the testis develops within the abdomen and usually descend about seven months during the foetal development
  • Around the seminiferous tubules is interstitial connective tissue which contains nerves and blood vessels, as well as one important cells type, the Leydig cells that produce testosterone. 


These notes were used to prepare for the reproductive biology exam, if there are any inaccuracies, feel free to point them in the comments section and we endeavour to rectify them.


Rizzo, D. C. (2015). Fundamentals of anatomy and physiology. Cengage Learning.

Sweeney, M. F., Hasan, N., Soto, A. M., & Sonnenschein, C. (2015). Environmental endocrine disruptors: effects on the human male reproductive system. Reviews in Endocrine and Metabolic Disorders16(4), 341-357.



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