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CheaperHibiscus4554

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sex hormones hormonal cycles reproductive health biology

Summary

This document outlines the process of sex hormone formation, focusing on the hypothalamic-pituitary-gonadal (HPG) axis. It details the roles of hormones like GnRH, FSH, LH, testosterone, and estrogen in both male and female puberty and reproductive cycles. The document also briefly touches on oral contraceptives and pregnancy.

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Sex Hormones Gonadotrophin Releasing Hormone : GnRH The first step in sex hormone formation is the release of the Gonadotropin Releasing Hormone from the hypothalamus GnRH is released in a PULSATILE fashion Rate of GnRH pulse affects subsequent FSH/LH release pattern Cont...

Sex Hormones Gonadotrophin Releasing Hormone : GnRH The first step in sex hormone formation is the release of the Gonadotropin Releasing Hormone from the hypothalamus GnRH is released in a PULSATILE fashion Rate of GnRH pulse affects subsequent FSH/LH release pattern Continuous administration of GnRH  Decreases FSH/LH Pituitary factors : Gonadotropins The anterior pituitary responds to GnRH by secreting gonadotropins: FSH= Follicular Stimulating Hormone LH = Luteinizing Hormone Although the effects of FSH and LH are quite different in males and females, a certain analogy exists : Gonadotropins act via two-cell system in males and females. Males LH FSH Leydig Sertoli cells cells Testosterone Spermatogenesis synthesis Females LH FSH Granulosa Cells Theca Cells Aromatase Activation Androgen Synthesis Estrogen Note: All Estrogen is synthesised from androgen precursors via aromatase enzyme Progesterone is first synthesised then converted to androgen precursors Females Biosynthesis of Sex Hormones Negative Feedback Testosterone inhibits Hypothalamic GnRH and pituitary FSH/LH secretion Estrogen: ↓ FSH/ ↓ LH, May also ↓GnRH High levels increase LH (LH surge) Estrogen + Progesterone: estrogen effect multiplied Progesterone alone may ↓GnRH pulse frequency ↓ Anterior pituitary responsiveness to GnRH Puberty It is initiated by hormonal signals from the brain to the gonads (HTH-P-G axis) LH FSH Hypothalamus less sensitive to gonadal steroids Puberty is not an isolated event It is a process which takes place over several years Male Puberty Generally starts between the ages of 11-12 Generally ends between the ages of 16-17 Characterized by the secretion of androgens Androgens Testosterone Androstenedione Dihydrotestosterone (DHT) The precursor of all estrogens (oestrogens) Biosynthesis of Sex Hormones Actions of Androgens Mainly Testosterone: Stimulate spermatogenesis (sperm production) The development of secondary sexual characteristics Male Puberty Male secondary sexual characteristics:  height and weight broadening shoulders (bone growth) muscle development (2x skeletal muscle) growth of the sexual organs pubic and facial hair growth voice deepening (thicker vocal folds) body odor (fatty acid composition of skin secretions, acne) Hypothalamic-pituitary- gonadal axis Luteinizing Hormone (LH) induces the production of testosterone from interstitial cells (Leydig) in the testes. Testosterone: stimulates secondary sex characteristics in males helps stimulate spermatogenesis in the testes (with FSH) sex drive (brain) Hypothalamic-pituitary- gonadal axis Androgens -Testosterone -Dihydrotestosterone (DHT): embryogenesis  Formation of gonads DHT produced locally (hair follicles)  DHT  Alopecia (androgenetic alopecia) Oestradiol Receptors in brain, penis, and testis Sexual appetite Erection Spermatogenesis Female Puberty Female puberty: generally starts between the ages of 10- 11 generally ends between the ages of 15- 17 characterized by the secretion of estrogens and progesterone: Follicular maturation Menstrual cycle the development of secondary sexual characteristics NORMAL MENSTRUAL CYCLE What is the mean duration of the MC? Mean 28 days (only 15% of women) Range 21-35 What is the average duration of menses? 2-7 days When does ovulation occur? Usually day 14 36 hrs after the onset of mid-cycle LH surge Female Hormonal cycle Cyclic changes in hormone levels  Periodicity of the ovulation Controlled by the hypothalamic-pituitary- gonads axis The Cycle Strongly linked to the endocrine system: hormone based  acts distant target (GnRH on pituitary) paracrine based  acts local (changes in the endometrium) During the course of a normal menstrual cycle: The ovaries go through 3 phases: 1.Follicular. 2.Ovulation. 3.Luteal. The endometrium goes through 3 phases: 4.Proliferative. 5.Secretory. 6.Menstruation. Follicular Phase FOLLICULAR PHASE Begins with menses on day 1 of the menstrual cycle & ends with ovulation RECRUITMENT MATURATION OF THE FOLLICLE SELECTION FOLLICULAR PHASE RECRUITMENT MATURATION OF THE FOLLICLE FSH  maturation of a cohort of ovarian follicles  only one reaches maturity Follicular Phase Maturation of primordial follicles into primary follicles FOLLICULAR PHASE SELECTION As the follicles mature   estrogen  FSH “-ve feed back on the pituitary”  the follicle with the highest number of FSH receptors will be selected The other follicles “that were recruited” will become atretic (breakdown) PREOVULATORY PERIOD NEGATIVE FEEDBACK ON THE PITUITARY - Estrogen (estradiol)  - feed back on pituitary   FSH POSITIVE FEEDBACK ON THE PITUITARY   estradiol (reaching a threshold concentration)   + feed back on the pituitary   LH surge  ovulation PREOVULATORY PERIOD LH SURGE Lasts for 48 hrs Ovulation occurs after 36 hrs Accompanied by rapid fall in estrogen level Granulosa cells  lutenization  progesterone synthesis Affects follicular wall  follicular rupture Luteal Phase Now empty follicle changes to a yellow colour, becomes corpus luteum Continues to secrete estrogen, but now beings to release progesterone Progesterone further develops uterine lining If pregnancy occurs  Human hCG Initially secreted by the trophoblast layer of the developing blastocyst hCG behaves like FSH and LH but it is NOT inhibited by a rising level of progesterone. hCG prevents the deterioration of the corpus luteum at the end of the fourth week Enables pregnancy to continue Menstruation If no embryo, the corpus luteum begins to disintegrate Progesterone levels drop, uterine lining detaches, menstruation can begin Tissue, blood, unfertilized egg all discharged Can take from 3-7 days MENSTRUATION The external hallmark of the menstrual cycle Periodic desquamation of the endometrium Prostaglandins are maximal in the endometrium just before menses Prostaglandins  constriction of the arterioles ischemia & desquamation Followed by arteriolar relaxation, bleeding & tissue breakdown hCG  Human chorionic gonadotropin (hCG) is a peptide hormone produced during pregnancy.  Good pregnancy marker: rapid rise in the concentration of hCG in the woman's urine hCG  Detectable concentration of hCG in urine 7-10 days after conception.  The concentration increases and reaches its maximum between the 8-11 weeks of pregnancy. Oral Contraceptives Combined oral contraception (COC) Contain estrogen and progesterone Most effective preparations 99% effective Progesterone only pill (POP) Offers an alternative when oestrogens are contraindicated If taken correctly 99% effective (no Mechanism of Action Estrogen & progesterone inhibit GnRH Preventing: FSH releases The mid-cycle surge of LH Ovulation There is no egg to be fertilized.

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