Puberty is simply defined as the biological changes of adolescence. Body composition begins to change. The circulatory and respiratory systems begin to change. The growth spurt usually triggers the feet and legs to grow, followed by the body's trunk and ending in the shoulders and chest. Bones become harder and more dense, while muscle and fat contribute to an adolescent increase in weight.
Sexual development involves enlargement, maturity and the reproduction of the primary sex organs.
For boys, the testes begin to produce part of the fluid for sperm cells and the prostate gland to produce semen. Males are able to ejaculate the semen, which contains the sperm. For girls, the ovaries release the mature ova into the fallopian tubes and menstruation occurs. The Teen Health Project at the Dalhousie Medical School in Nova Scotia, Canada examines all aspects of adolescent development including growth and human sexuality. According to the project, girls experience puberty about 2 years earlier than most boys.