FSH and LH

Luteinizing Hormone (LH)

Follicle Stimulating Hormone STRUCTURES, RECEPTORS AND PATHWAYS

go·nad·o·tro·pin (gō'nad-ō-trō'pin, gon'ă-dō-), Control of the reproductive axis originates in the hypothalamus with the periodic pulsatile release of gonadotropin-releasing hormone (GnRH). In response to GnRH (also called luteinizing hormone-releasing hormone or LHRH), the pituitary releases pulses of the gonadotropins, luteinizing hormone (LH) and follicle-stimulating hormone (FSH), into the blood stream. go·nad·o·tro·pin (gō'nad-ō-trō'pin, gon'ă-dō-), 1. A hormone capable of promoting gonadal growth and function; such effects, as exerted by a single hormone, are usually limited to discrete functions or histologic components of a gonad, such as stimulation of follicular growth or of androgen formation; most gonadotropins exert their effects in both genders, although the effect of a given gonadotropin will differ in males and females. 2. Any hormone that stimulates gonadal function. 3. Any substance that has the combined effects of follicle-stimulating hormone and luteinizing hormone.

Structure: Heterodimeric glycoprotein with 2 subunits :Luteinizing Hormone Males: stimulates testosterone production in males Females: triggers ovulation and stimulates progesterone secretion Structure: Heterodimeric glycoprotein with 2 subunits α (92 amino acids) – same as α subunits in FSH, TSH & hCG β (120 amino acids) – binds with LH receptors Secreted in anterior pituitary after stimulation from the hypothalamus via GnRH (gonadotropin-releasing hormone) Shares same pathway of secretion as FSH Regulated in negative feedback loop in men, and both negative and positive feedback loop in women

stimulates ovary to produce steroids FSH LH Female stimulates ovary to produce steroids ovary will produce estradiol during follicular phase and progesterone during luteal phase surge at midcycle, with LH, triggers ovulation surge at midcycle triggers ovulation remember, luteinizing hormone turns the follicle into the corpeus luteum by triggering ovulation Male stimulates Sertoli cells stimulating spermatogenesis. FSH also stimulates Sertoli cells to produce inhibin, which provides negative feedback to the anterior pituitary to decrease FSH secretion stimulates Leydig cells to produce testosterone testosterone provides negative feedback to anterior pituitary and hypothalamus

LH Triggers Puberty LH and FSH levels are elevated from birth until 6 months Development of secondary sex characteristics (puberty) is triggered by LH During puberty, hypothalamus secrete more GnRH ⇧ GnRH => ⇧ LH (and FSH) => ⇧ sex steroid hormones => development of secondary sex characteristics

Testes have 2 main “compartments: Seminiferous tubules – Sertoli cells for spermatogenesis Interstitial tissue – Leydig cells for testosterone secretion

Follicular Phase: Ovulation: Luteal Phase: FSH stimulates growth of follicle which stimulates estradiol secretion Increase in FSH & estradiol stimulates production of LH receptors on graafian cells during late follicular phase LH surge: rise in estradiol increases frequency of GnRh pulses and increases ability of pituitary to respond to GnRH with ⇧LH (positive feedback) Ovulation: LH surge causes graafian follicle to burst Luteal Phase: LH stimulates empty follicle to become restructured into corpus luteum and secrete progesterone in addition to estradiol Increase in progesterone inhibits GnRH, which inhibits LH & FSH (negative feedback) Fall in ovarian hormones causes menstruation

ENDOGENOUS PATHWAY OF FSH IN FEMALES