The human reproductive systems are two sets of organs that are both physiologically and anatomically different, one possessed by the male and the other by the female. These two organs, when working together, act to reproduce human life. The male reproductive system produces the male hormone testosterone and is responsible for the transfer of sperm from the male to the female reproductive system. Sperm cells (or spermatozoa) are produced in the testes and are activated during adolescence (around the 10th to 15th year of human life) to begin production. The testes are two separate glands within the male reproductive system and house a network of coiled tubes called the epididymis. These open into a singular vessel from one of the testes called the vas deferens or vas deferens. The testes are the sperm-producing facility that matures as it passes through the epididymis and will eventually be delivered to the female reproductive system to fertilize an egg. The pituitary gland at the bottom of the brain produces follicle-stimulating hormone (FSH) which controls sperm production. The vas deferens connect the epididymis of each testicle to the urethra in the prostate, a gland at the bottom of the bladder. Also at the prostate level, two sacs called seminal vesicles connect to each vas deferens via an ejaculatory duct. These vesicles secrete nutrient-rich seminal fluid as the sperm joins at the urethra to facilitate the sperm's journey to the female ovum (egg). At the same time, the seminal fluid is mixed with an alkaline fluid from the prostate to help the male ejaculate neutralize the acidic environment within the female reproductive system. By the time the ejaculate reaches the urethra, the composition of the male fluid is complete…half paper…new lining and a small amount of bleeding occurs. This cycle, however, is not renewed if an egg has been fertilized and implanted. The opening to the female reproductive system begins at the vagina. Its environment is kept moist with acidic secretions from the cervix to prevent bacterial microbes from entering the opening of the vagina. The vagina has two functions; to receive the male penis during intercourse and to serve as a birth canal during childbirth. The elasticity of the vagina helps this secondary purpose. During puberty, both in males and females, physiological, anatomical and hormonal changes occur. The main changes with respect to the reproductive system are; the sperm inside the male matures and is capable of fertilizing a mature female egg. The female begins her monthly menstrual cycle and is now capable of hosting a fertilized embryo.