Reproduction Physiology and Pathophysiology PDF

Reproduction Andrea C. Gore, PhD Professor, Division of Pharmacology and Toxicology [email protected] 1 Learning Objectives By the end of this lecture you will learn about: Reproductive physiology and the HPG axis Male reproductive physiology Female reproductive physiology Sexual develop...

Reproduction Andrea C. Gore, PhD Professor, Division of Pharmacology and Toxicology [email protected] 1 Learning Objectives By the end of this lecture you will learn about: Reproductive physiology and the HPG axis Male reproductive physiology Female reproductive physiology Sexual development, determination and differentiation, and puberty Gonadal sex steroid hormones, receptors, and steroidogenesis Sex and Reproduction Pregnancy, Placenta, Parturition Lactation Female Reproductive Disorders Male Reproductive Disorders 2 Introduction to Reproductive Physiology The reproductive system includes: Hypothalamus, pituitary, gonads – the HPG axis Reproductive tract and accessory sex glands External genitalia Reproduction requires gametogenesis (generation of sperm or ova) and steroidogenesis in both sexes, and ovulation in females. 3 Hypothalamicpituitarygonadal axis (HPG) 4 HPG Hormones, Receptors Hypothalamic hormone: Gonadotropin-releasing hormone (GnRH), also called luteinizing hormone-releasing hormone (LHRH) Pituitary hormones: Luteinizing hormone (LH) Follicle-stimulating hormone (FSH) Gonadal hormones: Estrogens (17b-estradiol) Androgens (testosterone) Progestins (progesterone) *The a subunit of LH, FSH and TSH is identical Peptide, 10 amino acids GnRH Receptor is GPCR Glycoproteins, made in gonadotropes, with common a (92 aa) and unique b subunits, (115 aa).* Receptors are GPCRs Steroids, derived from cholesterol Nuclear (genomic) receptors, and membrane (non-genomic) receptors 5 Male Reproduction Gonad: Primary sex organ, determined by XY genotype Reproductive Tract: System of specialized ducts that transport or house gametes after they are produced Accessory Sex Glands: make supportive fluids that are released into the reproductive tract External Genitalia Testis – site of spermatogenesis, steroidogenesis Epididymis Vas (ductus) deferens Ejaculatory duct Seminal vesicles Prostate gland Bulbourethral (Cowper’s) glands Penis, Scrotum 6 Male Gonad - Testis Testicular descent happens at ~7th month of gestation. Scrotum - allows for cooler temperature needed for spermatogenesis. Interstitial (Leydig) cells: steroidogenesis. Spermatogenesis takes place in seminiferous tubules (spheres of Sertoli cells) Sertoli cells are separated by tight junctions that create the blood-testis barrier. Coiled seminiferous tubules Testis Spermatozoa (sperm) 7 Male reproductive tract, glands, & genitalia Reproductive tract: Sperm passage from Epididymis (Capacitation – sperm gain ability to move and fertilize), then to vas deferens to ejaculatory duct Accessory sex glands: Seminal vesicles, Prostate, Bulbourethral Gland – secretions make up the bulk of semen. External genitalia: penis and scrotum 8 Spermatogenesis Go from undifferentiated diploid primordial germ cells (spermatogonia) to haploid spermatozoa (sperm). 64 day cycle. Three major stages 1. Mitotic proliferation 2. Meiosis (2 phases) 3. Packaging: Spermiogenesis ACG: You do not need to memorize these steps, but know that spermatogenesis involves both mitosis and meiosis and results in haploid sperm. 9 Sertoli cell & Developing Sperm Spermatozoan remains closely associated with Sertoli cells throughout development Functions of Sertoli cells Tight junction forms blood-testis barrier Sertoli cells provide nourishment to developing sperm. Secrete androgen-binding protein – maintains 100x more concentrated testosterone locally than in the blood Express testosterone receptor, FSH receptor. Release inhibin - provides negative feedback to FSH release. 10 Anatomy of a Spermatozoon Three functional parts: 1. Head - Consists primarily of the nucleus (contains DNA) and the Acrosome. The acrosome is: – Enzyme-filled vesicle cap used as an “enzymatic drill” to penetrate ovum – Formed by endoplasmic reticulum and Golgi complex before these organelles are discarded 2. Midpiece - concentrated mitochondria provide energy 3. Tail - Provides mobility 11 HPG axis Feedback Regulation Important points: Sertoli cell: spermatogenesis (in response to FSH) Leydig cell: steroidogenesis (in response to LH) Inhibin: made by Sertoli cell, negative feedback is selective to FSH secretion. 12 Plasma testosterone changes dynamically across the male life cycle, in coordination with reproductive development and needs 13 Female Reproduction Gonad: Primary sex organ, determined by XX genotype Ovary – site of oogenesis, ovulation, steroidogenesis Reproductive Tract: System of specialized ducts that house gametes after they are produced Accessory Sex Glands: make supportive fluids that are released into the reproductive tract External Genitalia Oviducts (Fallopian tubes) Uterus Upper vagina Secretions from glandular tissue in cervix, vaginal cells Vagina, clitoris, labia 14 Female Gonad - Ovary 15 Female Reproductive Tract Oviducts (Fallopian tubes) – Pick up oocyte on ovulation – Site for fertilization Uterus – Gestation – Parturition – Lowest portion, the cervix, projects to the vagina. Upper vagina – Muscular tube 16 Oogenesis Chromosomes in each cell Stages of oogenesis 46 (diploid number; single strands) Oogonium 1 Mitotic proliferation prior to birth (Arrested in first meiotic division) Primary oocytes After puberty, one primary oocyte reaches maturity and is ovulated about once a month until menopause ensues Enlarged primary oocyte 46 (diploid number; doubled strands) 46 (diploid number; doubled strands) (First meiotic division completed just prior to ovulation) First polar body Secondary oocyte 23 (haploid number; doubled strands) 2 Meiosis (Second meiotic division completed after fertilization) Second polar body Mature ovum Polar bodies degenerate 17 23 (haploid number; single strands) from ovum plus 23 (haploid number; single strands) from sperm for diploid fertilized ovum with 46 chromosomes Hormones and the Menstrual Cycle Follicular phase FSH/LH – follicle – E2 Follicle development - antrum formation – mature follicle Uterine proliferative phase E2 surge – preovulatory GnRH/LH surge Ovulation Luteal phase Corpus luteum – P4 Uterine secretory phase If no fertilization - corpus luteum degeneration- uterine menstrual phase (breakdown of endometrium) Fertilization - corpus Luteum of pregnancy v Feedback: negative or positive depending on the phase of the cycle 18 Development of the Follicle, Ovulation, and the Corpus Luteum 19 19 HPG Axis Feedback 20 Comparisons of spermatogenesis & oogenesis Both include chromosome replication and division during gamete production in both sexes Timing and end result are very different Spermatogenesis Oogenesis Accomplished within two months Takes anywhere from age 11 (puberty) to 50 (menopause) to complete on cyclic basis Postpubertal male can produce several hundred million sperm each day Female born with limited, largely nonrenewable supply of germ cells Each primary spermatocyte yields four equally viable spermatozoa Each primary oocyte yields only one cytoplasm-rich ovum and three cytoplasm-poor polar bodies that disintegrate 21 Menopause - Women Unique process in women (no true andropause in men – see slide 15) Cessation of woman’s menstrual cycle Usually occurs between 45 – 55 years Women don’t “run out” of ova due to ovulation – rather, it is due to age-related follicular atresia Preceded by period of progressive ovarian failure – Irregular cycles – dwindling ovarian estrogen levels (from as much as 300 mg/day to essentially nothing). – Loss of progesterone, androgens Period of transition called the climacteric = perimenopause Not a disease but rather a natural life change May be associated with pathological changes in bone, cardiovascular system, hot flashes, vaginal dryness 22 Menopause - Women from: BK Wich & M Carnes, Endocrinol & Metab Clin North America Vol 24, 273-295 (1995) 23 Menopause - Pathophysiology Although not a disease, menopause can be associated with physical and psychological changes that impair quality of life: Vasomotor symptoms – hot flashes, sweating/chills Psychological symptoms – irritability, anxiety, depression Urogenital changes to vaginal epithelium Osteoporosis Loss of libido 24 Menopausal Hormone Treatments (HT) Fact: The loss of ovarian hormones, especially estrogens, is causally linked to hot flashes, sleep disorders, and osteoporosis. Controversy: The Women’s Health Initiative (WHI) raised concerns that risks of HT outweighed benefits – very small increased risk of adverse cardiovascular events and breast cancer. Aftermath: Reanalysis of the WHI indicated that most participants were 65+ years old – more than 15 years post-menopause - and were disproportionately obese. Current recommendations: If risk factors for thrombembolism or breast cancer are absent, women with significant menopausal symptoms can benefit estrogen-progestin therapy (intact uterus) or estrogen alone therapy (hysterectomy). Women are recommended to use hormones for shortest 25 possible length of time. 4. Sexual Development, Determination & Differentiation, and Puberty Males and females differ by: – Genetic: XX, XY (SRY gene on Y-chromosome) – sex determination – Gonadal: Ovary, testis – Phenotypic: Apparent anatomic sex of individual. Usually determined by gonadal sex Other aspects of sexuality: – Hormonal (differences in levels of sex hormones) – Behavioral (receptive behaviors of females, mounting and penile intromission behaviors of males) – Psychological (gender identity) – Legal (birth certificate) 26 Disorders of sexual differentiation Genetic male fails to properly differentiate and secrete hormones à phenotypic female Genetic male lacks functional androgen receptor à phenotypic female Genetic male lacking DHT à internal organs are male but external genitalia are not fully masculinized Congenital adrenal hyperplasia (CAH): in females, excessive secretion of adrenal DHEA causes masculinization of female genitalia. XO female – Turner’s syndrome (45,X) – appear female but lack secondary sex characteristics, are short stature, and other characteristics. ACG: all of this is different from “sexual dysphoria” 27 Puberty & Adolescence Puberty: Maturational period associated with the attainment of adult reproductive function. – Females: Begins at 10-12 years – Males: Begins at 12-14 years – Both: lasts about 3-5 years Adolescence: The entire transitional period between childhood and adulthood, not just sexual maturation Puberty is driven by the brain – requires activation of GnRH neurons, driving pituitary gonadotropins, and subsequently, gonadal development and increased hormone synthesis and release. 28 Secondary Sexual Characteristics External (phenotypic) characteristics that are not directly involved in reproduction, but which distinguish males and females Typically develop during puberty Usually due to differences in absolute or relative levels of sex steroid hormones – Androgens: most important for masculine qualities (deeper voice, body morph) – Estrogens: most important for feminine qualities (female “curves”, breasts) 29 Gonadal sex steroid hormones, receptors, and steroidogenesis Progestins (progesterone) Androgens (testosterone, DHT) Estrogens (estradiol, estrone, estriol) In circulation, bind to binding globulins or albumin. Androgens, estrogens: sex hormone binding globulin (SHBG) Progestins: Corticosteroid-binding globulin (CBG) When bound, activity is reduced or eliminated. Free hormone exerts biological actions. Metabolism of steroids takes place in the liver. Excretion occurs in the urine. 30 Testosterone as precursor to DHT, 17β-Estradiol Testosterone P450 aromatase 17β-estradiol 5α reductase 5a-dihydrotestosterone31 (5α-DHT) 31 Steroidogenesis MALES: In the testis Leydig cells synthesize androgens and secrete them into the bloodstream. FEMALES: In the ovary – Thecal cell (LH receptor): cholesterol à androgen – Granulosa cell (FSH receptor): androgen à estrogen. 32 Androgens - Physiology Testosterone (T) is the principal androgen in men, but DHT is more potent. ~ 40% of T binds to sex-hormone binding globulin (SHBG)biounavailable. ~ 60% of T binds to albumin with low affinity - may become unbound and available for binding to the androgen receptor (AR). 1-2% of T is “free” to act upon the AR. [Testosterone] Across Life Cycle Goodman & Gilman Fig. [T] in women is ~30-50 ng/dl; made by the corpus luteum and adrenals 33 Androgen Effects Reproductive system before birth – Masculinization of the reproductive tract, external genitalia; testicular descent into scrotum (w/ proteins) Sex-specific tissues after birth – Growth & maturation of reproductive system at puberty, and maintenance at adulthood; spermatogenesis Other reproductive-related effects in both sexes – Libido – Negative feedback regulation of gonadotropins Secondary sexual characteristics – Male hair growth; vocal changes; muscle growth. – Females: axillary hair (underarm, pubic) Non-reproductive actions – Protein anabolism; bone growth at puberty & epiphyseal plate closure after conversion to estrogen outside of testes by aromatase; may induce aggressive behavior 34 Estrogens - Physiology Estriol 17b-estradiol 17β-estradiol: Most potent natural estrogen, produced at highest levels in the gonads. Estrone: Major form formed in peripheral tissues from androgen. Estriol: Major estrogen secreted by the placenta Estrone Estrone and estriol are also produced by metabolism of estradiol in the liver. Estrone is also synthesized from adrenal DHEA, and in adipose tissue in postmenopausal women. All three estrogens circulate in the blood, and are excreted in the urine. The placenta synthesizes estrone and estriol from fetal DHEA. 35 Estrogen Effects Formation of female secondary sex characteristics Reproductive tract: – Stimulates endometrial growth – Uterine growth – Vaginal lubrication Skeleton: Bone growth and remodeling Cardiovascular: Coagulation Fat metabolism Maintenance of vessels and skin Brain: mood, learning 36 Progesterone Progesterone Progesterone is the most abundant natural progestin in men and women. In the ovary, progesterone is largely produced by the corpora lutea. It is also synthesized in testis, adrenal cortex and placenta. In males, progesterone may partner with androgens in some actions, including reproduction. In circulation: Bound by albumin and corticosteroid-binding globulin (CBG). 37 Progesterone Effects Neuroendocrine systems: feedback onto the GnRH system Reproductive tract: causes endometrium to become secretory; if fertilization doesn’t occur, P declines and results in menstruation Endocervical glands: P causes thickening of secretions, and decrease sperm penetration Pregnancy: P is crucial to maintenance of pregnancy Mammary gland: P is involved in gland development; at late pregnancy, contributes to mammary gland cell proliferation Brain: involved in basal body temperature (mechanism is unknown); depressant actions in the brain. Metabolism: increases [insulin]; enhances fat deposition 38 Gonadal Steroid Hormone Receptors Estrogen receptors Nuclear ERs (ERα and ERβ) are homologous (44% aa identity) but produced off of two different genes. Membrane ER (GPR30) - GPCR Progestin receptors One nuclear PR gene with two isoforms, PRA and PRB, synthesized off of two different promoters. Androgen receptor One known nuclear AR, binds testosterone and its metabolites (DHT), the latter with higher affinity. There is now known to be a membrane AR. Receptors are widely distributed through brain & body, reflecting the diverse actions of steroids. 39 Sex & Reproduction Males: Erection – Pathophysiology: Erectile Dysfunction (ED) Ejaculation Females: Fertilization or conception Gestation or pregnancy Parturition Lactation 40 Males: Penile Erection Erection: engorgement of penile erectile tissue with blood. Two long chambers in the penis, the corpora cavernosa, contain columns of spongelike vascular tissue. The arterioles that supply these vascular chambers are usually constricted. Erection requires a sequence of events: 1. Sensory (mechanoreceptors in penis) or mental stimulation. 2. The brain sends impulses to local nerves in the penis, causing muscles of the corpora cavernosa to relax, and allowing blood to flow in and fill the spongelike tissues. 3. Pressure makes the penis expand. 4. A membrane sheath around the corpora cavernosa, called the tunica albuginea, helps trap blood. 5. Erection ends after climax or arousal has passed. Veins open and blood flows back out into the body. 41 Males: Ejaculation Ejaculation – also a spinal reflex. Two phases: Emission – Emptying of semen (sperm and fluids) into the urethra – Due to sympathetic impulses causing contraction of smooth muscles in the walls of ducts and accessory sex glands Expulsion – Expulsion of semen from the penis – Semen triggers nerve impulses that cause rhythmic contraction of skeletal muscles at base of penis 42 Erectile Dysfunction (ED) https://www.niddk.nih.gov/health-information/urologic-diseases/erectile-dysfunction ED is present when a man: Can get an erection sometimes but not every time. Can get an erection but it doesn’t last long enough for intercourse. Is unable to get an erection. ED is more common as men age, and affects 30 million of men in the US. Prevalence of ED with age: Younger than 60: 12% 60-69: 22% 70 years+: 30% Identify and treat the underlying causes of ED: Address lifestyle changes Change or adjust medications Counseling 43 Erectile Dysfunction (ED) - Causes Causes of or contributors to ED: High blood pressure Diabetes Atherosclerosis Overweight, obese Heart and blood vessel disease Chronic kidney disease Multiple sclerosis Injuries from treatments for prostate cancer, including radiation and surgery Surgery for bladder cancer Peyronie’s disease (scar tissue, called plaque, forms in penis) Lifestyle: smoking, alcohol, certain drugs, sedentary lifestyle Psychological or emotional issues: anxiety, depression, fear of sexual failure, stress Side effect of common medications used to treat BP, antihistamines, antidepressants, tranquilizers, appetite suppressants, ulcer medications. Low testosterone: Not usually a cause. Oral medications: most work to relax smooth muscle and increase blood flow in the penis 44 during sexual stimulation Fertilization in females Sperm travels up the female reproductive tract – optimal site of fertilization is oviduct – upper third (ampulla) Fuses with plasma membrane of ovum – Triggers chemical change in ovum’s surrounding membrane that makes outer layer impermeable to entry of any more sperm – Head of fused sperm gradually pulled into ovum’s cytoplasm – Within an hour, sperm and egg nuclei fuse Fertilized ovum now called a zygote Optimally occurs within 24 hours after ovulation – Sperm usually survive about 48 hours but can survive up to 5 days in female reproductive tract 45 Sperm transport during fertilization 46 Process of Fertilization ACG words to know: Corona radiata Zona pellucida Acrosome reaction 47 Pregnancy, Placenta, Parturition Fertilized ovum (zygote) divides mitotically – Within week grows and differentiates into morula then blastocyst capable of implantation Blastocyst implants in endometrial lining by means of enzymes released by trophoblasts – Enzymes digest endometrial tissue Carve hole in endometrium for implantation of blastocyst Release nutrients from endometrial cells for use by developing embryo 48 Ovum cross section) From Fertilization to Implantation Blastocyst (cross section) Inner cell Morula Cleavage Spermatozoa mass Head of fertilizing spermatozoon Destined to become fetus Trophoblast Accomplishes implantation and develops into fetal portions of placenta Fertilization Polar bodies Secondary oocyte (ovum) Ovulation Implantation Ovary Endometrium of uterus 49 Implantation of Blastocyst Blastocyst adheres to the endometrial lining, and trophoblastic cell cords begin to penetrate Trophoblastic cells tunnel deeper, carving out hole for blastocyst At completion of implantation, the blastocyst is completely buried in the endometrium 50 Formation of Placenta & Amniotic sac * 51 51 Placenta Organ of exchange between maternal and fetal blood Acts as transient, complex endocrine organ that secretes essential pregnancy hormones: – Human chorionic gonadotropin (hCG) – basis of pregnancy tests » Maintains corpus luteum until placenta takes over function in last two trimesters » CL of pregnancy secretes estrogens and progestins – Estrogen » Essential for maintaining normal pregnancy - stimulates growth of myometrium; estriol promotes mammary gland duct development – Progesterone » Essential for maintaining normal pregnancy - suppresses uterine contraction, forms mucus plug in cervical canal, stimulates development of breast milk glands 52 Secretion Rates of Placental Hormones 53 The placenta plays a key role in steroidogenesis Estriol 54 Other placental hormones Human chorionic somatomammotropin (hCS) – increases glucose and fatty acid availability to fetus and protect against fetal hypoglycemia. Parathyroid hormone-related peptide (PTHrp) mobilizes calcium from maternal bones to ensure calcification of fetal bones (happens when the mother does not consume enough calcium) Relaxin – Softens the cervix and loosens connective tissue between pelvic bones in preparation for delivery 55 Gestation Pregnancy (or gestation) – About 38 weeks from conception (40 weeks from LMP or ~37 weeks from implantation) – Physical changes within mother to meet demands of pregnancy Uterine enlargement Breasts enlarge and develop ability to produce milk Volume of blood increases 40% Weight gain Respiratory activity increases by about 20% Urinary output increases Kidneys excrete additional wastes from fetus Nutritional requirements increase 56 Parturition Labor, delivery, birth Requires – Dilation of cervical canal to accommodate passage of fetus from uterus through vagina and to the outside – Contraction of uterine myometrium that are sufficiently strong to expel fetus Exact factors triggering increase in uterine contractility and initiating parturition not fully established 57 Parturition - Hormones Relaxin - cervical softening Nuclear Factor kB (NF-kB) in uterus - increases oxytocin receptors CRH - from fetal portion of placenta - stimulates fetal adrenal synthesis of DHEA which drives placental estrogen secretion; also involved in development of fetal lungs Estrogen – increases oxytocin receptors in myometrium Oxytocin – Causes stronger contractions – Positive-feedback cycle progressively increases until cervical dilation and delivery are complete 58 Lactation Prolactin (ant. Pituitary) – milk protein synthesis Oxytocin (post. Pituitary) – milk letdown 59 Breast milk Colostrum is milk produced in first 5 days with particularly high immunoglobulin content IgA made in breast lymphocytes – confers passive immunity on the newborn. Mucus - adheres to microorganisms and prevent absorption Lactoferrin - decreases iron availability which is needed for pathogen multiplication Bifidus factor - promotes multiplication of nonpathogenic microorganisms, Lactobacillus bifidus 60 Female Reproductive Disorders Polycystic ovary syndrome (PCOS) Menstrual disorders Abnormal vaginal bleeding Infertility Preeclampsia-eclampsia 61 Polycystic ovarian syndrome (PCOS) Occurs in 2-5% reproductive age women Typically obese with hyperinsulinemia, insulin resistance, dyslipidemia Elevated plasma androgens and estrogens (estrone) 62 Menstrual Disorders – Amenorrhea, Dysmenorrhea Amenorrhea: Lack of menstrual bleeding May be due to uterine disorders (problems with endometrium), ovarian problems (anovulation, ovarian insufficiency), hormone feedback problems, pituitary or hypothalamic disorders (usually due to trauma) Dysmenorrhea: Pain and other symptoms during menstruation Symptoms include sweating, weakness, insomnia, GI problems, back pain, headache, dizziness Due to disordered prostaglandin (PGF2a) production, usually overproduction, by the secretory endometrium Can be due to endometriosis Can be accompanied by PMS 63 Abnormal vaginal bleeding Excess vaginal bleeding, or irregular bleeding. Pathogenesis: Endocrine disorder Structural lesions that alter the endometrial cavity; includes polyps, fibroids Malignancy – Unopposed estrogen can lead to endometrial cancer – this is why women with a uterus who use estrogen also get a progestin Blood clotting disorders 64 Female infertility A couple is infertility if there is 12+ months of unprotected sex without conception. About 15% of couples are infertile, about 50:50 for male and female causes. 65 Preeclampsia-Eclampsia Occurs in ~5% of pregnancies in the US Hypertension, proteinuria, and edema One of the most common causes of maternal death in developed countries. 66 Male Reproductive Disorders Male infertility Benign prostatic hyperplasia (BPH) Erectile dysfunction (see earlier) 67 Male Infertility A couple is infertile if there is 12+ months of unprotected sex without conception. About 15% of couples are infertile, about 50:50 for male and female causes. May be due to defects at: – Hypothalamus or pituitary – Testicles – problems with production and maturation of sperm – Post-testicular – problems with sperm transport, ejaculation 68 Benign prostatic hyperplasia (BPH) Nonmalignant growth of the prostate stroma and epithelial glands, resulting in enlargement of the prostate gland. Clinical symptoms occur in 1/3 of men over 65 years Etiology is unknown, although age and hormone status play roles. 69 BPH - Pathogenesis Aging is associated with prostatic hyperplasia Prostatic capsule – may cause obstruction and pressure on the bladder Roles of hormones: – Androgens (especially DHT) – therefore 5α-reductase blockers are used clinically, as are androgen receptor blockers – Estrogens – induce androgen receptors Roles of growth factors: – Fibroblast growth factors (FGFs), especially FGF7, stimulates growth of prostate epithelial cells. – Transforming GFs (TGFs), especially TGFβ, inhibit cell growth. – IGFs also play an inhibitory role 70 Learning Objectives By the end of this lecture you will learn about: Reproductive physiology and the HPG axis Male reproductive physiology Female reproductive physiology Sexual development, determination and differentiation, and puberty Gonadal sex steroid hormones, receptors, and steroidogenesis Sex and Reproduction Pregnancy, Placenta, Parturition Lactation Female Reproductive Disorders Male Reproductive Disorders 71