Development of the human body used to approximately judge a child's age based on physical development. Puberty is the process of physical changes through which a child's body matures into an adult body capable of sexual reproduction. It is initiated by hormonal signals from the brain to the gonads: the ovaries in a girl, the testes in a boy. In response to the signals, the gonads produce hormones that stimulate libido and the growth, function, and transformation of the brain, bones, muscle, blood, skin, hair, breasts, and sex organs. Physical growth—height and weight—accelerates in the first half of puberty and is completed when an adult
Theology of the Body not address whether it was expedient or not to marry, but pointed out that there are "eunuchs" and some are so willingly for the sake of the kingdom of heaven. The fifth cycle discusses the sacrament of marriage. Pope John Paul II began his discussion of contraception on 11 July 1984 with the 114th lecture in this series. This section of the lecture series, the sixth and final part, is largely a reflection on "Humanae vitae", the 1968 encyclical of Pope Paul VI. In it, John Paul continued his emphasis on the design of the human body revealing God's truths.