The male reproductive system produces sperm, or male gametes, and passes them to the female reproductive system. Sperm are produced in the testes (also called testicles), which are housed externally in a sac-like structure called the scrotum. The scrotum contracts and relaxes to move the testes closer or farther from the body. This process keeps the testes at the appropriate temperature for sperm production, which is slightly lower than regular body temperature.
Mature sperm are stored in the epididymis. During sexual stimulation, sperm travel from the epididymis through a long, thin tube called the vas deferens. Along the way, the sperm is joined by fluids from three glands to form semen. The seminal vesicles secrete the bulk of the fluid which makes up semen, which is composed of various proteins, sugars, and enzymes. The prostate contributes an alkaline fluid that counteracts the acidity of the vaginal tract. Finally, the Cowper gland secretes a protein-rich fluid that acts as a lubricant. Semen travels through the urethra and exits the body through the penis, which becomes rigid during sexual arousal.
The main hormone associated with the male reproductive system is testosterone, which is released by the testes (and in the adrenal glands in much smaller amounts). Testosterone is responsible for the development of the male reproductive system and male secondary sexual characteristics, including muscle development and facial hair growth.
The female reproductive system produces eggs, or female gametes, and gestates the fetus during pregnancy. Eggs are produced in the ovaries and travel through the fallopian tubes to the uterus, which is a muscular organ that houses the fetus during pregnancy. The uterine cavity is lined with a layer of blood-rich tissue called the endometrium. If no pregnancy occurs, the endometrium is shed monthly during menstruation.
Fertilization occurs when the egg absorbs the sperm; it usually takes place in the fallopian tubes but may happen in the uterus itself. After fertilization the new zygote implants itself in the endometrium, where it will grow and develop over thirty-eight weeks (roughly nine months). During gestation, the developing fetus acquires nutrients and passes waste through the placenta. This temporary organ is attached to the wall of the uterus and is connected to the baby by the umbilical cord.
When the fetus is mature, powerful muscle contractions occur in the myometrium, the muscular layer next to the endometrium. These contractions push the fetus through an opening called the cervix into the vagina, from which it exits the body. The placenta and umbilical cords are also expelled through the vagina shortly after birth.
The female reproductive cycle is controlled by a number of different hormones. Estrogen, produced by the ovaries, stimulates Graafian follicles, which contain immature eggs cells. The pituitary gland then releases luteinizing hormone, which causes the egg to be released into the fallopian tubes during ovulation. During pregnancy, estrogen and progesterone are released in high levels to help with fetal growth and to prevent further ovulation.
Common pathologies of the male and female reproductive systems include infections, cancers, and dysfunction.