Do you remember those uncomfortable days in school, when you’d squirm in shame on your chair while you were learning about human reproduction and the anatomy of the male reproductive system for the first time? Then you should consider we’re making a short recap of the information you got then. As opposed to women, whose sex organs are entirely inside the body, the male reproductive organs are located both outside and inside the body and they include:
- Scrotum
- Testicles
- Sperm ducts
- Sexual glands
- Penis
The scrotum is a pouch-like organ made of skin and muscles, which holds and protects the testicles. It is located under the penis, in the pubic area. The scrotum consists of two adjoining pouches, each of them holding a testicle. The smooth muscles in the scrotum allow regulating the distance between the testicles and the rest of the body. When the temperature of the testicles increases above the limit for spermatogenesis, the scrotum relaxes, bringing down the testicles away from the body. On the contrary, the scrotum contracts and brings the testicles closer to the body heat when the temperature drops below the minimum value of the ideal interval for sperm formation.
The two testicles are the male glands responsible for sperm and testosterone production. They are ellipsoidal glandular organs, with a size ranging from 3.5-5 cm in length and about 2.5 cm in diameter. Each testicle, held in its own pouch in the scrotum, is connected to the abdomen through a sperm duct and a special muscle, also associated to the muscles in the scrotum for temperature regulation. The inside of the testicles is divided into small compartments called lobules. Each lobule contains a section of tiny seminiferous tubes (producing sperm cells), lined with epithelial cells. These epithelia (membranes) contain numerous stem cells which divide constantly and form sperm cells in the process called spermatogenesis.
The epididymis is an area that stores sperm cells, coiling around the upper part and the back of each testicle. The epididymis is made of a tube with a total length of about 2 metres, which looks like a compact mass of coils. The sperm produced in the testicles moves to the epididymis to mature before being carried to the reproductive organs. This is precisely the role played by the epididymis: delaying the release of sperm, allowing it to mature.
Inside the scrotum, a pair of sperm ducts connect the testicles to the abdominal cavity. These sperm ducts contain the nerves, veins, arteries and lymphatic vessels that support the testicles’ functioning. In addition, they contain the ductus deferentes (or vasa deferentia), two tiny tubes that carry sperm cells from the epididymis to the abdominal cavity, towards the ejaculatory duct. The vasa deferentia have a larger diameter than the epididymis’ tubes, and their inside is used to store mature sperm cells. The smooth muscles of the vasa deferentia push the seminal fluid, through peristalsis, towards the ejaculatory duct.
The seminal vesicles are a pair of exocrine glands of an irregular shape, which produce and store some of the fluid that composes the semen. This fluid contains proteins and mucus and has an alkaline pH to allow sperm cells to survive in the acidic vaginal environment. The fluid also contains fructose, which feeds spermatic cells so that they can survive for as long as possible and fertilise the egg.
The vasa deferentia pass through the prostate (are surrounded by it) and join the urethra, forming the structure known as the ejaculatory duct. During ejaculation, the duct opens and releases the sperm and the secretions of the seminal vesicles into the urethra.
The seminal fluid goes from the ejaculatory duct and comes out of the body by crossing the urethra, a long muscular tube 20-25 cm in length. The urethra crosses the prostate and opens at the end of the external urethral meatus, located at the tip of the penis. Urine follows the same route during the excretion process, when it is released from the bladder.
The prostate is an exocrine gland the size of a walnut, located under the bladder, around the urethra. The prostate produces a significant part of the fluid that eventually becomes sperm. This fluid has a milky colour and contains enzymes, proteins and other substances that support and protect sperm cells during ejaculation. The prostate also has smooth muscles, which can contract to prevent urine or the seminal fluid from dripping.
Underneath the prostate there are a pair of exocrine glands the size of a pea, called Cowper’s glands (or bulbourethral glands). They secrete into the urethra a thin alkaline fluid that lubricates the urethra and neutralises the acidity of any remaining urine after urination. This fluid enters the urethra during sexual foreplay, before ejaculation, preparing the urethra for the passage of sperm.
The penis is the external male sexual organ, located above the scrotum and below the navel. The penis has a more or less cylindrical shape and contains the last part of the urethra and the external urethral opening. The large alveoli inside the penis tissue allow it to be filled with blood, facilitating erection. The erection of the penis makes it harder, longer and thicker. The function of the penis is to carry the sperm into the vagina during intercourse. Aside from the reproductive function, the penis allows the release of urine through the urethra.
The semen is the fluid produced by males for sexual reproduction, ejaculated from the body during intercourse. Semen contains sperm cells (or spermatozoa), male reproductive cells, along with a series of other substances, suspended in a fluid material. The chemical composition of semen gives it a thick, sticky consistency and a slightly alkaline pH. These characteristics allow it to support reproduction by helping the sperm cells after sexual intercourse. The sperm are helped to remain inside the vagina, and the acidity of the vaginal environment is neutralised. In healthy adult males, one mililitre of semen contains about 100 million sperm cells. These male reproductive cells are designed to fertilise the egg inside the woman’s Fallopian tubes.