The puberty and the hormonal and physical modifications. Representation for the boy and for the girl of the changes observed during puberty at the level of genital organs, of the areas on silhouettes of sexual secondary characters and other developped specifically thanks to the secretion of testosterone for the boy and estrogen for the girl. It is the hypothalamus that triggers the processus of puberty in boys at 13-14 years old and in girls at 10-11 years old. The pituitary gland secretes lh (luteinizing hormone) and FSH (follicle-stimulating hormone) towards the testicles in boys and the ovaries in girls, in charge of making sexual cells. Testicles and ovaries stimulate the production of sexual hormones that enclenchent the internal and external transformations of the body.