Puberty is the process o pheesical changes through which a bairn's body maturs intae an adult body capable o sexual reproduction tae enable fertilisation. It is initiatit bi hormonal signals frae the brain tae the gonads: the ovaries in a girl, the testes in a boy. In response tae the signals, the gonads produce hormones that stimulate libido an the growth, function, an transformation o the brain, banes, muscle, bluid, skin, hair, breasts, an sex organs. Pheesical growth—hicht an wicht—accelerates in the first hauf o puberty an is completit when the bairn haes developed an adult body. Till the maturation o their reproductive capabilities, the pre-pubertal pheesical differences atween boys an girls are the external sex organs.