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
The Description of the Human Body He believed the heat of the heart somehow caused all movement of the body. Blood vessels he realized were pipes, he saw that veins carried digested food to the heart. (This was brought further by William Harvey. Harvey developed the idea of the circulation of the blood.) Descartes felt that an energetic part of blood went to the brain and there gave the brain a special type of air imbued with vital force that enabled the brain to experience, think and imagine. This special air then went through the nerves to the muscles enabling them to move. The Description of