الفهرس Only 14 pages are availabe for public view
 |  | from | 151 |  |  |
| | | from | 151 | | |
Abstract
Puberty is a critical human development process that leads to sexual maturation and reproductive capability. It requires an intact hypothalamic pituitary gonadal axis (HPG). Any disruption of this axis can result in temporary or permanent disorders of reproductive endocrine function. The HPG axis is active during fetal development and continues to function in infancy until it enters a relative quiescent state. Pubertal onset is heralded by the re-emergence of the pulsatile secretion of hypothalamic GnRH. GnRH stimulates gonadotropin in the anterior pituitary gland to secret lutenizing hormone and follicle stimulating hormone that in turn bind to ligand specific receptors in the gonads , causing gonadal maturation and production of sex steroids, most notably testosterone and esradiol . This process is termed gonadarche. Testosterone and estradiol together with inhibin, activin and others regulate the subsequent activity of the hypothalamus and pituitary gland. Puberty is a dynamic period of physical growth, sexual maturation and psychosocial achievement that generally begins in boys between 9-14 years. The factors that regulate the onset of puberty remain elusive. Certainly, environmental and metabolic factors are critical regulators of HPG axis and the timing of puberty, but their influence on puberty is dependant on significant genetic control. Gene GPR54 appears to be a signal for the beginning of puberty in human beings. Leptin plays an important role in signaling nutritional status to the central reproductive axis and appears to be at least a permissive factor in the initiation of puberty. Combination of these factors lead to the pulsatile secretion of GnRH. Mutation in GPR54 in human causes hypogonadotropic hypogonadism, pubertal delay and sexual infantilism that can be corrected by administration of exogenous GnRH in pulsatile manner. The standard clinical system for describing normal pubertal development and its variations is the five stage system (Tanner staging). The Tanner stages of puberty are based on the development of the genitalia and pubic hair distribution.
Testicular enlargement and increase in scrotal folds and pigmentation are the first clear signs of true puberty in boys. The onset of testicular enlargement occurs at age of 9.5- 13.5 year, then development of secondary sexual characters. Adrenarche is the puberty of the adrenal gland, the phenotypic result of adrenarche is pubarche or the development of axillary’s and pubic hair that appears in boys at about age 8 years. The phenomenon of adrenarche is unique to human beings. The sexual precocity is the appearance of any sign of secondary sexual maturation before the age of nine years in boys. Precocity due to early activation of the pulse generation of hypothalamic GnRH is known as central or GnRH dependant precocious puberty.