Structures of the male reproductive system include testes, accessory glands, penis, semen, and hormones.
The testes are located outside the abdominal cavity, suspended in a sac called the scrotum, which is between the thighs. Each of the two testis (singular) is surrounded by a tough fibrous connective tissue capsule.
The word for the testes originated in the Greek and so named for its oval shape – orchis. Orchis was dubbed by Aristotle and is still the medical term used today, as in orchitis, an inflammation of the testicles. The actual word testis came from the Latin meaning to bear witness, sharing the same root word with testify.
In ancient Rome, as well as in the Bible, only men could bear witness or testify in a public forum. In order to show importance to their testimony, they would hold their testicles as they spoke. An oath was declared while holding another’s testicles.
Each testis is divided into about 250 smaller units called lobules. Each lobule contains seminiferous tubules and interstitial cells. Seminiferous tubules form sperm. Interstitial cells produce the male hormones called androgens.
The testes contain two types of hormone-producing cells: interstitial and sustentacular.
- Interstitial cells produce the steroid hormones known as androgens. The most important is testosterone, which does the following:
- promotes the production of functional sperm;
- maintains the secretory glands of the male reproductive tract;
- determines the secondary sex characteristics: for example, the distribution of facial hair and body fat;
- controls aggressiveness and sexual desire;
- is equally critical for both men and women as it increases lean muscle and red blood cell mass, stimulates GH (growth hormone) release, and increases the metabolic rate.
- Sustentacular cells are directly associated with the formation and function of the sperm, and secrete a hormone called inhibin, which occurs under FSH stimulation. Inhibin depresses this secretion by the anterior pituitary gland. Throughout adult life, these two hormones interact to maintain normal levels of sperm production.
The penis has two functions:
- carry urine to the outside;
- a reproductive organ.
The shaft or body of the penis contains three columns of erectile tissue. The enlarged tip is called the glans penis. The loose skin that forms a cuff around the glans is called the foreskin or prepuce.
At the time of puberty, small glands located in the foreskin and the glans secrete an oily substance. This substance, along with the surrounding dead cells, forms a cheesy compound called smegma. Therefore, daily hygiene should include pulling back the foreskin for cleansing to avoid infections.
Sperm cannot live at body temperature (37°C or 98.6°F). It prefers temperatures of 34°C (93.2°F). Wearing tight underwear or jeans will elevate temperatures, thus lowering sperm count.
Most sperm live only a few hours after being deposited in the female reproductive tract, but some can survive for as long as three days.
Each day, millions of sperm are formed by the epithelium of the seminiferous tubules, which contain two types of cells:
- spermatogenic cells, which produce sperm
- supporting cells, also called sustentacular cells, Sertoli cells (or nurse cells). These cells support, nourish, and regulate the spermatogenic cells.
Sperm has three parts:
- Head, which contains the nucleus with all the genetic information. The front part of the head has a specialized structure called the acrosome which contains enzymes that helps penetrate the egg at the time of fertilization.
- Body, or midpiece, which is a spiral-shaped structure that contains the mitochondria and supplies the sperm with the needed energy for propulsion.
- Tail, which is the flagellum which enables the sperm to move in a whip-like fashion.
As sperm form, they gather in the siminiferous tubules and then move into a series of genital ducts, where they mature before being transported from the testes to the outside. The ducts include:
- two epididymes;
- two vas ductus deferens;
- two ejaculatory;
- one urethra.
- Prostate Gland: The prostate gland secretes a milky alkaline substance that increases sperm motility and counteracts the acidic environment of the female vagina. During ejaculation, the smooth muscle of the prostate gland contracts, forcing the secretions into the urethra. About 60% of the seminal volume comes from the seminal vesicles, with the rest coming from the prostate gland.
- Bulbourethral glands (Cowper glands) are tiny glands that secrete a thick mucus into the male urethra to serve as a lubricant during sexual intercourse.
- Epididymis is a tightly coiled duct that measures about 6 or 7 meters (20 to 23 feet) in length. Each of the two epididymis ducts connects each testis to the ductus deferens and is the site of sperm maturation.
- Vas ductus deferens (sperm duct) conducts sperm between epididymis and prostate.
- Seminal vesicles secrete fluid that makes up much of the volume of semen.
- Urethra conducts semen and urine to exterior.