Male Genitalia/Reproductive System
The Male Reproductive System
The purpose of the organs of the male reproductive system is to perform the following functions:
- To produce, maintain, and transport sperm (the male reproductive cells) and protective fluid (semen)
- To discharge sperm within the female reproductive tract during sex
- To produce and secrete male sex hormones responsible for maintaining the male reproductive system
Unlike the female reproductive system, most of the male reproductive system is located outside of the body.
These external structures include the penis, scrotum, and testicles.
- Penis: This is the male organ used in sexual intercourse. It has three parts: the root, which attaches to the wall of the abdomen; the body, or shaft; and the glans, which is the cone-shaped part at the end of the penis. The glans, also called the head of the penis, is covered with a loose layer of skin called foreskin. This skin is sometimes removed in a procedure called circumcision. The opening of the urethra, the tube that transports semen and urine, is at the tip of the penis. The glans of the penis also contains a number of sensitive nerve endings.
- The body of the penis is cylindrical in shape and consists of three circular shaped chambers. These chambers are made up of special, sponge-like tissue. This tissue contains thousands of large spaces that fill with blood when the man is sexually aroused. As the penis fills with blood, it becomes rigid and erect, which allows for penetration during sexual intercourse. The skin of the penis is loose and elastic to accommodate changes in penis size during an erection.
- Semen, which contains sperm (reproductive cells), is expelled (ejaculated) through the end of the penis when the man reaches sexual climax (orgasm). When the penis is erect, the flow of urine is blocked from the urethra, allowing only semen to be ejaculated at orgasm.
- Scrotum: This is the loose pouch-like sac of skin that hangs behind and below the penis. It contains the testicles (also called testes), as well as many nerves and blood vessels. The scrotum acts as a "climate control system" for the testes. For normal sperm development, the testes must be at a temperature slightly cooler than body temperature. Special muscles in the wall of the scrotum allow it to contract and relax, moving the testicles closer to the body for warmth or farther away from the body to cool the temperature.
- Testicles (testes): These are oval organs about the size of large olives that lie in the scrotum, secured at either end by a structure called the spermatic cord. Most men have two testes. The testes are responsible for making testosterone, the primary male sex hormone, and for generating sperm. Within the testes are coiled masses of tubes called seminiferous tubules. These tubes are responsible for producing sperm cells.
The internal organs of the male reproductive system, also called accessory organs, include the following:
- Epididymis: The epididymis is a long, coiled tube that rests on the backside of each testicle. It transports and stores sperm cells that are produced in the testes. It also is the job of the epididymis to bring the sperm to maturity, since the sperm that emerge from the testes are immature and incapable of fertilization. During sexual arousal, contractions force the sperm into the vas deferens.
- Vas deferens: The vas deferens is a long, muscular tube that travels from the epididymis into the pelvic cavity, to just behind the bladder. The vas deferens transports mature sperm to the urethra, the tube that carries urine or sperm to outside of the body, in preparation for ejaculation.
- Ejaculatory ducts: These are formed by the fusion of the vas deferens and the seminal vesicles (see below). The ejaculatory ducts empty into the urethra.
- Urethra: The urethra is the tube that carries urine from the bladder to outside of the body. In males, it has the additional function of ejaculating semen when the man reaches orgasm. When the penis is erect during sex, the flow of urine is blocked from the urethra, allowing only semen to be ejaculated at orgasm.
- Seminal vesicles: The seminal vesicles are sac-like pouches that attach to the vas deferens near the base of the bladder. The seminal vesicles produce a sugar-rich fluid (fructose) that provides sperm with a source of energy to help them move. The fluid of the seminal vesicles makes up most of the volume of a man's ejaculatory fluid, or ejaculate.
- Prostate gland: The prostate gland is a walnut-sized structure that is located below the urinary bladder in front of the rectum. The prostate gland contributes additional fluid to the ejaculate. Prostate fluids also help to nourish the sperm. The urethra, which carries the ejaculate to be expelled during orgasm, runs through the center of the prostate gland.
- Bulbourethral glands: Also called Cowper's glands, these are pea-sized structures located on the sides of the urethra just below the prostate gland. These glands produce a clear, slippery fluid that empties directly into the urethra. This fluid serves to lubricate the urethra and to neutralize any acidity that may be present due to residual drops of urine in the urethra.
How Does the Male Reproductive System Function?
The entire male reproductive system is dependent on hormones, which are chemicals that regulate the activity of many different types of cells or organs. The primary hormones involved in the male reproductive system are follicle-stimulating hormone, luteinizing hormone, and testosterone.
Follicle-stimulating hormone is necessary for sperm production (spermatogenesis), and luteinizing hormone stimulates the production of testosterone, which is also needed to make sperm. Testosterone is responsible for the development of male characteristics, including muscle mass and strength, fat distribution, bone mass, facial hairgrowth, voice change, and sex drive.
Structure of the Male Reproductive System
By Irvin H. Hirsch, MD
- The penis and the urethra are part of the urinary and reproductive systems.
- The scrotum, testes (testicles), vas deferens, seminal vesicles, and prostate comprise the rest of the reproductive system.
The penis consists of the root (which is attached to the lower abdominal structures and pelvic bones), the visible part of the shaft, and the glans penis (the cone-shaped end). The opening of the urethra (the channel that transports semen and urine) is located at the tip of the glans penis. The base of the glans penis is called the corona. In uncircumcised males, the foreskin (prepuce) extends from the corona to cover the glans penis.
The penis includes three cylindrical spaces (sinuses) of erectile tissue. The two larger ones, the corpora cavernosa, occur side-by-side. The third sinus, the corpus spongiosum, surrounds most of the urethra. When these spaces fill with blood, the penis becomes large and rigid (erect).
The scrotum is the thick-skinned sac that surrounds and protects the testes. The scrotum also acts as a climate-control system for the testes because they need to be slightly cooler than body temperature for normal sperm development. The cremaster muscles in the wall of the scrotum relax to allow the testes to hang farther from the body to cool or contract to pull the testes closer to the body for warmth or protection.
The testes are oval bodies that average about 1.5 to 3 inches (4 to 7 centimeters) in length and 2 to 3 teaspoons (20 to 25 milliliters) in volume. Usually the left testis hangs slightly lower than the right one. The testes have two primary functions:
- Producing sperm (which carry the man's genes)
- Producing testosterone (the primary male sex hormone)
The epididymis is a collection of coiled microscopic tubes that together are almost 20 feet (6 meters) long. The epididymis collects sperm from the testis and provides the environment for sperm to mature and acquire the ability to move through the female reproductive system and fertilize an ovum. One epididymis lies against each testis.
The vas deferens is a firm tube (the size of a strand of spaghetti) that transports sperm from the epididymis. One such duct travels from each epididymis to the back of the prostate and joins with one of the two seminal vesicles. In the scrotum, other structures, such as muscle fibers, blood vessels, and nerves, also travel along with each vas deferens and together form an intertwined structure, the spermatic cord.
The urethra serves a dual function in males. This channel is the part of the urinary tract that transports urine from the bladder and the part of the reproductive system through which semen is ejaculated.
The prostate lies just under the bladder and surrounds the urethra. Walnut-sized in young men, the prostate enlarges with age. When the prostate enlarges too much, it can block urine flow through the urethra and cause bothersome urinary symptoms.
The seminal vesicles, located above the prostate, join with the vas deferens to form the ejaculatory ducts, which travel through the prostate. The prostate and the seminal vesicles produce fluid that nourishes the sperm. This fluid provides most of the volume of semen, the fluid in which the sperm is expelled during ejaculation. Other fluid that makes up a very small amount of the semen comes from the vas deferens and from Cowper glands in the urethra.
Male Reproductive Organs
What is the male reproductive system?
The organs and structures of the male reproductive system give men the ability to fertilise a woman's egg (ovum) to produce a baby. Several different organs and structures make up the male reproductive system. These include:
The scrotum, or scrotal sac. This is the loose bag of skin which hangs under the main body cavity between the upper thighs. It is divided into two, and each side contains one testicle (testis).
The testicles (testes). There are two testes. Each is an egg-shaped structure located in the scrotum. The testes produce sperm and also produce male hormones. The testes start developing inside the body cavity in a growing baby (fetus). About two months before a male baby is born, the testes start to drop down into the scrotal sacs. Because they are outside the main body cavity the testes are slightly cooler. This difference in temperature helps sperm production.
The epididymis. This is the tube attached to the testis where sperm is stored.
The vas deferens. This is the tube which carries the sperm from the epididymis. It meets a tube from the seminal vesicle (see below) to form a short tube called the ejaculatory duct. This then opens into the urethra, which is the tube that takes the sperm outside the body.
The accessory sex glands. There are three glands which produce fluids that mix with the sperm to make up semen. Semen is the liquid which is ejected from the penis during ejaculation. The three glands are located close to the bladder and are called:
- The seminal vesicles
- The prostate gland. The prostate gland lies just beneath the bladder (see diagram). It is normally about the size of a chestnut.
- The bulbourethral glands
The penis. The penis has a single tube in it called the urethra. There are three main parts of the penis - the root, body and glans. The root is the part attached to the skin at the top of the scrotum. The body of the penis is made up of a spongy type of tissue, which swells when blood enters during an erection. The glans penis is the slightly larger area towards the end of the penis and contains the opening of the urethra.
The urethra. This is the tube which passes from the bladder down the penis to the outside. It carries both urine and semen.
What does the male reproductive system do?
The main function is to give men the ability to fertilise a woman's egg (ovum) by producing and delivering semen. The testicles (testes) also make hormones which help men develop the characteristics associated with being male. This includes:
- The development of hair in a male distribution - for example, on the chest, under the arms, on the face and in the pubic area.
- Enlargement of the penis.
- Deepening of the voice.
- Muscle growth.
- Bone growth and increased height.
How does the male reproductive system work?
During puberty, the level of a hormone called gonadotrophin-releasing hormone (GnRH) increases. GnRH is produced in a part of the brain called the hypothalamus. In turn this causes an increase in the production of two hormones from another part of the brain, called the pituitary gland. These hormones are called luteinising hormone (LH) and follicle-stimulating hormone (FSH). LH in the bloodstream causes cells in the testicles (testes) to make and release testosterone, the main male hormone.
FSH and testosterone work together to stimulate the testes to produce sperm. Each sperm cell takes between 65-75 days to form and around 300 million are produced every day. Inside the testes sperm is made in structures called the seminiferous tubules. At the top and to the back of each testicle (testis) is the epididymis, which stores sperm.
Leading from the epididymis is the vas deferens. The vas deferens carries sperm towards the penis. Along the way it joins other tubes and during ejaculation collects fluids from the accessory sex glands. The mixture of sperm and fluids from the accessory sex glands is called semen. About two thirds of the volume of semen come from the seminal vesicles. The semen is then passed into the urethra.
When sexually aroused, a number of changes occur inside the penis. The arteries supplying the penis get bigger, allowing more blood to enter its tissues. The extra blood flow causes the penis to enlarge and to become more rigid. The extra blood flow plus signals from the nervous system and chemical changes cause an erection.
Ejaculation is the term for the contractions that release semen. This is a reflex action, which means it is not consciously controlled. As part of the reflex action, the opening that drains the bladder is closed. This means that urine is not released at the same time as semen. The volume of semen in a typical ejaculation is between 2.5-5 millilitres (mL). There are normally more than 20 million sperm in each mL of semen. During sexual intercourse, the penis of the male enters the vagina of the female, carrying the sperm to the neck of the womb (cervix) to fertilise the woman's egg.
Some disorders of the male reproductive system
Facts on The Male Anatomy
The male reproductive system includes the following structures:
- Testes (testicles)
- Vas deferens
- Seminal vesicles
Anatomy of the Male Torso
The penis consists of three main parts: the root, the body, and the glanspenis.
1. The root is attached to the abdominal and pelvic wall.
2. The body is the middle portion. The body of the penis consists of three cylindrical spaces of soft tissue. When the two larger spaces fill with blood, the penis becomes large and rigid, forming an erection.
- Two larger cylindrical spaces of soft tissue, called the corpora cavernosa, are located side by side and form the bulk of the penis.
- The third cylindrical space of soft tissue, called the corpus spongiosum, surrounds the urethra, which forms the urinary passage.
3. The glans penis is the cone-shaped end or head of the penis, which is the termination of the corpus spongiosum. The small ridge that separates the glans penis from the shaft or body of the penis is called the corona.
The scrotum is a thin sac of skin and thin muscle in which lie the testicles. The scrotum acts as a climate control system, allowing the testicles to be slightly away from the rest of the body and keeping them slightly cooler than normal body temperature for optimal sperm development. The muscles in the scrotum, called the cremasteric muscles, move the testicles slightly within the scrotum depending on the surrounding temperature.
The testes (or testicles) are two olive-sized oval bodies, one on the right side and one on the left side. The testes have two main functions:
- to produce sperm (the male reproductive cell), and
- to produce testosterone (the male sex hormone).
The epididymides and the vasa deferentia are attached to the testicles and are important in transporting sperm cells after they develop in the testes.
The term testicles includes the testes as well as the surrounding structures, such as the vas deferens and the epididymis. These two names, testes and testicles, are often used interchangeably even though their definitions are slightly different.
Vas Deferens and Seminal Vesicles
Once sperm are produced, they travel through a collection area, called the epididymis, and then through a tube or duct, called the vas deferens, which then joins the seminal vesicles to form the ejaculatory duct. The seminal vesicles produce a fluid that provides nutrients for the sperm and lubricates the urethra. This fluid mixes with other fluids to create the semen.
During ejaculation, muscles surrounding the seminal vesicles contract and push out the sperm and the fluid from the seminal vesicles, much like squeezing a tube of toothpaste. The seminal vesicles are located behind the prostate and the bladder.
The prostate is a walnut-sized gland that lies below the urinary bladder and surrounds the urethra. Along with the seminal vesicles, the prostate gland produces a fluid, called prostatic fluid, that contains, protects, nourishes, and supports the sperm. The white, sticky fluid originally from the prostate forms most of the volume of the semen. The prostate has no known function other than reproduction.
The prostate grows throughout life. This growth often causes a blockage in the urethra that affects voiding with such symptoms as urinary frequency, excessive urination at night (nocturia), urgency of urination, and weakening of the urinary stream. This enlargement of the prostate, called benign prostatic hyperplasia (or BPH), can be treated with medication or various surgical procedures.
The prostate is also the source of a prostate specific antigen (or PSA) that is used as a blood test to detect and monitor prostate cancer.
Picture of the Prostate Gland
The urethra is surrounded by the corpus spongiosum, one of the cylindrical spaces of soft tissue of the penis described earlier. In men, the urethra provides a dual purpose:
- to transport urine from the bladder, and
- to transport the semen (sperm cells and fluid from the seminal vesicles and the prostate) out the tip of the penis.
Scar tissue in this passage, called strictures, can cause urinary difficulty.