The male reproductive organs are the testes (or testicles). The testes are two egg-shaped organs located in a pouch called the scrotum outside the body. In the scrotum, the temperature is a few degrees cooler than body temperature. The testes develop in the abdominal cavity before birth, and then descend to the scrotum.
Sperm production in the testes takes place within coiled passageways called seminiferous tubules. Within the walls of these tubules, primitive cells called spermatogonia undergo a series of changes and proceed through meiosis to yield sperm cells. Each human sperm cell has 23 chromosomes.
The sperm cells mature in a tube called the epididymis. The epididymis is located along the surface of the testes. The hormone that stimulates sperm cell production is the follicle-stimulating hormone (FSH). A second hormone important in reproduction is the interstitial cell-stimulating hormone (ICSH), which acts on interstitial cells located between the seminiferous tubules. The interstitial cells secrete male hormones, including testosterone. The male hormones regulate the development of secondary male characteristics.
The organ responsible for carrying the sperm cells to the female is the penis. Within the penis, the sperm cells are carried in a tube, the urethra. During periods of sexual arousal, the penis becomes erect as blood fills its spongelike tissues. The sperm cells are mixed with secretions from the prostate gland, seminal vesicles, and Cowper's glands. These secretions and the sperm cells constitute the semen.
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