Why changes in the body occur at adolescence?

The changes occurring in body at adolescence is mainly controlled by the action of hormones, Hormones are chemical substance secreted by endocrine gland that reaches to a particular body part via bloodstream. Changes in boys like production of sperms, growth of beard and moustaches, growth of hair on chest, under the arms and in pubic region are all because of release of male hormone testosterone and changes in girls like production of ova, development of breast, development of mammary gland inside the breast, growth of hair under the arms and in pubic region are all because of the female hormone estrogen produced by ovaries.