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Luteinizing Hormone (LH) Will McNees Physiology 3 November 28, 2016 LH Overview Gonadotropic 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 LH Regulation 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 Less GABA inhibition Glutamate stimulation GnRH => LH (and FSH) => sex steroid hormones => development of secondary sex characteristics LH in Males Testes have 2 main “compartments: Seminiferous tubules – Sertoli cells for spermatogenesis Interstitial tissue – Leydig cells for testosterone secretion LH in Males LH receptors found exclusively on Leydig cells Directly stimulates testosterone secretion by Leydig cells Indirectly stimulates spermatogenesis by Sertori cells Regulated by testosterone in negative feedback loop Secretion of LH & FSH is relatively constant LH in Males LH in Males LH in Women Follicular 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 LH in Women LH in Women Questions The release of __________ by the __________ causes the secretion of LH & FSH by the __________. What substances cause inhibition of LH? What cells contain receptors for LH in males? What event triggers ovulation? What does LH stand for? Answers The release of GnRH by the hypothalamus causes the secretion of LH & FSH by the anterior pituitary. What substances cause inhibition of LH? Testosterone and progesterone What cells contain receptors for LH in males? Leydig cells in interstitial tissue of testes What event triggers ovulation? LH surge What does LH stand for? Luteinizing hormone
