This leaflet gives a brief overview of the male reproductive system.
The organs and structures of the male reproductive system give men the ability to fertilise a woman's ovum (egg) to produce a baby.
Several different organs and structures make up the male reproductive system. These include the testes, where sperm is made, several ducts (tubes) where sperm is stored, and the penis. The penis has a single duct called the urethra; this releases both sperm and urine. Also included in the male reproductive system are the accessory sex glands, which include the prostate gland and seminal vesicles. These glands make special fluids, which are added to sperm as it travels through the ducts. Together the liquid is known as semen.
Hormones are also made by parts of a man's reproductive system.
The testes start developing inside the internal body cavity in a growing baby (fetus). About two months before a male baby is born, the testes start to descend 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 penis contains the urethra, which passes both urine and semen. There are three main parts of the penis - the root, body and glans. The root is the part attached to the lower abdomen. 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.
Its main function is to give men the ability to fertilise a woman's ovum by producing and delivering semen. The testes also make hormones which help men develop the characteristics associated with being male. This includes the distribution of pubic hair, enlargement of the penis and deepening of the voice.
During puberty, levels of certain hormones in the brain begin to increase. These changes cause an increase in the production and release of two hormones from the pituitary gland - luteinising hormone (LH) and follicle-stimulating hormone (FSH). (The pituitary gland is a small gland at the base of the brain. It makes various hormones which are released into the bloodstream, including LH and FSH.) LH in the bloodstream causes cells in the testes to make and release testosterone, another hormone. Some of this testosterone gets converted into another form. Together, the two forms of testosterone help to develop and enlarge the penis and other male sex organs. Testosterone also helps to encourage muscle and skeletal growth and deepen the male voice.
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 testis is the epididymis, which stores sperm.
Leading from the epididymis is the vas deferens. The vas deferens carries sperm to the penis. To do this, the vas deferens passes into the internal cavity of the body. Passing close to the bladder, the vas deferens eventually enters the prostate gland where the tube becomes the urethra.
The prostate gland lies just beneath the bladder (see diagram). It is normally about the size of a chestnut. The prostate gland makes a specialised fluid which is added to sperm during ejaculation. The seminal vesicles also add fluid to the sperm during ejaculation.
The mixture of sperm, fluid from the prostate and fluid from the seminal vesicles is called semen. About 60-70% of the volume of semen comes from the seminal vesicles. The urethra (the tube which transports urine and semen) runs through the middle of the prostate.
When sexually aroused, a number of changes occur inside the penis. The arteries supplying the penis expand allowing more blood to enter its tissues. The increase in blood flow causes the penis to enlarge. The extra blood flow plus signals from the nervous system and chemical changes cause an erection. Ejaculation (the contractions that release semen) 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) with more than 20 million sperm per mL.
From Gray's Anatomy Online
From Wikibooks, the open-content textbooks collection