Development and Puberty By: Amber Martinez and gabby madrigal

Puberty Puberty is the process of physical changes through which a child's body matures into an adult body capable of sexual reproduction to enable fertilization. It is initiated by hormonal signals from the brain to the gonads: the ovaries in a girl, the testes in a boy.

Process The Y chromosome contains a gene called SRY, which stands for “sex- determining region Y.” The gene encodes a protein called a transcription factor, which controls when other genes are transcribed- in other words, when they are switched on or off. By regulating other genes, the SRY gene acts as molecular switch that triggers a cascade of events leading to the development of male sex organs. A zygote with a normal Y chromosome, therefore, becomes a male. A zygote without a Y chromosome will develop into a female.

Embryonic and Fetal Development Fifth week: reproductive organs begin to develop Sixth and seventh week: male and female embryos are visually indistinguishable because they first develop in the same way in both males and females Seventh week: SRY gene starts to take effect in embryos that have a Y chromosome – male organs begin to develop starting with the testes. The cells in the developing testes secrete testosterone, which causes the penis, scrotum, and male accessory organs to develop. Embryos without and SRY gene will start to develop in the eighth week. Female organs and external genitals begin to develop Final two months: Testes descend from the pelvic cavity to the scrotum in males. In females the ovaries descend somewhat, but they remain within the pelvis cavity.

Normal hormonal control of puberty

The initial stimulus for puberty is elevated secretion of gonadotropin-releasing hormone, or GnRH. This hormone is secreted by the hypothalamus in the brain. GnRH causes the pituitary gland to produce more follicle-stimulating hormone. In turn, FSH and LH stimulate production of gonadal hormones – testosterone in males, and estrogen in females. The rising levels of gonadal hormones stimulate maturation of the reproductive organs, and cause the appearance of secondary sex characteristics.

Males First physical phase of puberty is marked by growth of the scrotum and testes. Followed by secondary sex characteristics appearing: pubic and axillary hair growth, an increase in the size of the larynx and the length of the vocal folds causes the voice to deepen The penis grows larger in proportion to the body size Unexpected erections at unexpected times Occasional emission of semen during sleep – nocturnal emission By the end of puberty mature sperm are present in semen Epiphyseal plates close and the long bones in the body stop growing.

Females First phase marked by breast growth Followed by development of secondary sex characteristics: growth of underarm hair, gradual changes in the width of the pelvis and size of pelvic outlet to facilitate pregnancy and childbirth. Skeletal growth accelerates After about 2 years from beginning puberty the first menstrual bleeding occurs. At this time epiphyseal plates in long bones close causing height growth to stop