Question

a. Describe the two mechanisms that have been proposed to explain the rise in sex steroid secretion that occurs at puberty. Explain the possible effects of body fat and intense the positive role of melatonin in reproduction.

Answer 1

a.The mechanisms by which rise in sex hormones occurs at puberty are as follows -

1.Hypothalamic-pituitary gonadal feedback mechanism (HPG)

At the time of puberty, the hypothalamic pituitary gonadal axis gets activated through the secretion of estrogen from ovaries in female and testosterone from the testes in male.It starts with the release of gonadotrophin releasing hormone (GnRH) from the hypothalmus via GnRH expressing hormones.GnRH flows down to the anterior pituitary gland via hypophyseal portal system and bound to the secretory cell receptor of adenohypophysis. Further, activated GnRH activates the secretory cells of adenohypophysis to release the LH and FSH hormones and allow them to travel in blood stream.In females LH and FSH hormones,activate the ovaries to stimulate the estrogen(Female Sex hormone) and inhibin to regulate the ovarian cycle.Estrogen maintains the negative feedback loop with GnRH in the hypothalamus. Where as in males, LH activates the interstitial cells in testes and release testosterone (Male Sex hormone) and FSH helps in spermatogenesis.

2.Growth hormone mechanism

GH activates FSH induced granulosa cell differentiation directly and hence increases the ovarian IGF-1 level and enhances the ovarian response to gonadotrophin . As a result it enhances the gonadotrophin effect on granulosa cells.GH works synergistically with GnRH secretion for ovarian maturation.The local accumulation of Growth hormone and IGF-1 generates a intraovarian paracrine control on steroidogenesis .The similar mechanism applies for the testosterone production as well during puberty.