Y khoa, y dược - The reproductive system: Part C

27 The Reproductive System: Part CEstablishing the Ovarian CycleDuring childhood, until pubertyOvaries secrete small amounts of estrogensEstrogen inhibits release of GnRHEstablishing the Ovarian CycleAt pubertyLeptin from adipose tissue decreases the estrogen inhibition GnRH, FSH, and LH are releasedIn about four years, an adult cyclic pattern is achieved and menarche occursHormonal Interactions During a 28-Day Ovarian CycleDay 1: GnRH  release of FSH and LHFSH and LH  growth of several follicles, and estrogen release estrogen levelsInhibit the release of FSH and LHStimulate synthesis and storage of FSH and LH Enhance further estrogen outputHormonal Interactions During a 28-Day Ovarian CycleEstrogen output by the vesicular follicle increasesHigh estrogen levels have a positive feedback effect on the pituitary at midcycleSudden LH surge at day 14 Hormonal Interactions During a 28-Day Ovarian CycleEffects of LH surgeCompletion of meiosis I (secondary oocyte continues on to metaphase II)Triggers ovulationTransforms ruptured follicle into corpus luteumHormonal Interactions During a 28-Day Ovarian CycleFunctions of corpus luteumProduces inhibin, progesterone, and estrogenThese hormones inhibit FSH and LH releaseDeclining LH and FSH ends luteal activity and inhibits follicle developmentHormonal Interactions During a 28-Day Ovarian CycleDays 26–28: corpus luteum degenerates and ovarian hormone levels drop sharply Ends the blockade of FSH and LHThe cycle starts anewFigure 27.19HypothalamusLate follicular andluteal phases 1122234556887 Slightlyelevated estrogen and rising inhibin levels. Positivefeedback exerted by large inestrogen output.Mature follicleCorpus luteumOvulatedsecondaryoocyteRupturedfollicleLH surgeProgesteroneEstrogenInhibinHypothalamusEarly and midfollicular phasesTravels viaportal bloodGranulosacellsInhibinAndrogensConvertandrogens toestrogensThecalcellsAnterior pituitaryGnRHFSHLHFigure 27.20a(a) Fluctuation of gonadotropin levels: Fluctuating levels of pituitary gonadotropins (follicle-stimulating hormone and luteinizing hormone) in the blood regulate the events of the ovarian cycle.FSHLHFigure 27.20b(b) Ovarian cycle: Structural changes in the ovarian follicles during the ovarian cycle are correlated with (d) changes in the endometrium of the uterus during the uterine cycle.PrimaryfollicleSecondaryfollicleVesicularfollicleOvulationCorpusluteumDegeneratingcorpus luteumFollicularphaseOvulation(Day 14)LutealphaseUterine (Menstrual) CycleCyclic changes in endometrium in response to ovarian hormonesThree phases Days 1–5: menstrual phaseDays 6–14: proliferative (preovulatory) phaseDays 15–28: secretory (postovulatory) phase (constant 14-day length) Uterine CycleMenstrual phaseOvarian hormones are at their lowest levelsGonadotropins are beginning to riseStratum functionalis is shed and the menstrual flow occursUterine Cycle Proliferative phaseEstrogen levels prompt generation of new functional layer and increased synthesis of progesterone receptors in endometriumGlands enlarge and spiral arteries increase in numberUterine Cycle Secretory phaseProgesterone levels promptFurther development of endometriumGlandular secretion of glycogenFormation of the cervical mucus plug Figure 27.20c(c) Fluctuation of ovarian hormone levels: Fluctuating levels of ovarian hormones (estrogens and progesterone) cause the endometrial changes of the uterine cycle. The high estrogen levels are also responsible for the LH/FSH surge in (a).ProgesteroneEstrogensFigure 27.20d(d) The three phases of the uterine cycle: • Menstrual: Shedding of the functional layer of the endometrium. • Proliferative: Rebuilding of the functional layer of the endometrium. • Secretory: Begins immediately after ovulation. Enrichment of the blood supply and glandular secretion of nutrients prepare the endometrium to receive an embryo.Both the menstrual and proliferative phases occur before ovulation, and together they correspond to the follicular phase of the ovarian cycle. Thesecretory phase corresponds in time to the luteal phase of the ovarian cycle. MenstrualphaseMenstrualflowEndometrialglandsBlood vesselsFunctional layerBasal layerProliferativephaseSecretoryphaseDaysUterine CycleIf fertilization does not occurCorpus luteum degeneratesProgesterone levels fallSpiral arteries kink and spasmEndometrial cells begin to dieSpiral arteries constrict again, then relax and open wideRush of blood fragments weakened capillary beds and the functional layer sloughsEffects of Estrogens Promote oogenesis and follicle growth in the ovaryExert anabolic effects on the female reproductive tractSupport the rapid but short-lived growth spurt at pubertyEffects of EstrogensInduce secondary sex characteristicsGrowth of the breastsIncreased deposit of subcutaneous fat (hips and breasts)Widening and lightening of the pelvisEffects of EstrogensMetabolic effectsMaintain low total blood cholesterol and high HDL levelsFacilitates calcium uptakeEffects of ProgesteroneProgesterone works with estrogen to establish and regulate the uterine cycleEffects of placental progesterone during pregnancyInhibits uterine motilityHelps prepare the breasts for lactationFemale Sexual ResponseInitiated by touch and psychological stimuliThe clitoris, vaginal mucosa, and breasts engorge with bloodVestibular gland secretions lubricate the vestibule Orgasm is accompanied by muscle tension, increase in pulse rate and blood pressure, and rhythmic contractions of the uterusFemale Sexual ResponseFemales do not have a refractory period after orgasm and can experience multiple orgasms in a single sexual experienceOrgasm is not essential for conceptionSexually Transmitted Infections (STIs)Also called sexually transmitted diseases (STDs) or venereal diseases (VDs)The single most important cause of reproductive disordersGonorrheaBacterial infection of mucosae of reproductive and urinary tractsSpread by contact with genital, anal, and pharyngeal mucosae GonorrheaSigns and symptomsMalesUrethritis, painful urination, discharge of pus Females20% display no signs or symptomsAbdominal discomfort, vaginal discharge, or abnormal uterine bleedingCan result in pelvic inflammatory disease and sterilityTreatment: antibiotics, but resistant strains are becoming prevalentSyphilisBacterial infection transmitted sexually or contracted congenitallyInfected fetuses are stillborn or die shortly after birthInfection is asymptomatic for 2–3 weeksA painless chancre appears at the site of infection and disappears in a few weeksSyphilisIf untreated, secondary signs appear several weeks later for 3–12 weeks, and then disappear: pink skin rash, fever, and joint painThe latent period may or may not progress to tertiary syphilis, characterized by gummas (lesions of the CNS, blood vessels, bones, and skin)Treatment: penicillinChlamydiaMost common bacterial STI in the United StatesResponsible for 25–50% of all diagnosed cases of pelvic inflammatory diseaseSymptoms: urethritis; penile and vaginal discharges; abdominal, rectal, or testicular pain; painful intercourse; irregular mensesCan cause arthritis and urinary tract infections in men, and sterility in womenTreatment: tetracyclineViral InfectionsGenital warts Caused by human papillomavirus (HPV)Second most common STI in the United StatesIncrease the risk of cancers in infected body regionsViral InfectionsGenital herpesCaused by human herpes virus type 2Characterized by latent periods and flare-upsCongenital herpes can cause malformations of a fetusTreatment: acyclovir and other antiviral drugsDevelopmental Aspects: Determination of Genetic Sex One of the 23 pairs of chromosomes in body cells are sex chromosomes: X and YFemales are XX and each egg has an X chromosomeMales are XY, so ~50% of sperm contain X, ~50% contain YDevelopmental Aspects: Determination of Genetic SexX egg + X sperm  XX (female offspring)X egg + Y sperm  XY (male offspring)The SRY gene on the Y chromosome initiates testes development and malenessDevelopmental Aspects: Sexual DifferentiationSexually indifferent stageGonads begin development in fifth week as gonadal ridgesParamesonephric (Müllerian) ducts (future female ducts) form lateral to the mesonephric (Wolffian) ducts (future male ducts)Primordial germ cells migrate to the gonadal ridges to provide germ cells destined to become spermatogonia or oogoniaGonads begin development in seventh week in males, eighth week in femalesFigure 27.21 (1 of 5)MesonephrosGonadal ridgeMetanephros(kidney)5- to 6-week embryo:sexually indifferent stageMesonephric(Wolffian) ductParamesonephric(Müllerian) ductCloacaFigure 27.21 (2 of 5)Paramesonephricduct (degenerating)TestesMesonephric ductforming the ductusdeferensUrinary bladderSeminal vesicleUrogenital sinusforming the urethraEpididymisEfferent ductules7- to 8-week male embryoFigure 27.21 (3 of 5)Ovaries8- to 9-week female fetusParamesonephricduct forming theuterine tubeMesonephric duct(degenerating)Fusedparamesonephricducts forming the uterusUrinary bladder(moved aside)Urogenital sinusforming the urethraand lower vaginaDevelopmental Aspects: Development of External GenitaliaGenital tubercle  penis of male; clitoris of femaleUrethral fold  urethra of male; labia minora of femaleLabioscrotal folds  scrotum of male: labia majora of femaleFigure 27.22aUrethral foldLabioscrotalswellingUrethral grooveGenitaltubercleAnusTail (cut)(a) IndifferentFigure 27.22bGlans penisPenisScrotumAnus(b) Male developmentUrethralfolds Glans penisLabioscrotalswellings(scrotum)AnusApproximately 5 weeksFigure 27.22aUrethral foldLabioscrotalswellingUrethral grooveGenitaltubercleAnusTail (cut)(a) IndifferentFigure 27.22c(c) Female developmentAnusLabia majoraGlans clitorisLabiaminoraAnusLabioscrotalswellings(labia majora)Glans clitorisUrogenitalsinusUrethralfolds(labiaminora)Approximately 5 weeksDevelopment Aspects: Descent of the GonadsAbout two months before birthTestosterone stimulates the migration of the testes toward the scrotumOvaries also descend, but are stopped by the broad ligament at the pelvic brimGubernaculum: fibrous cord from each testis to the scrotum or from ovary to labium majus; guides the descentFigure 27.21 (4 of 5)TestisPenisUrinary bladderSeminal vesicleEpididymisUrethraDuctus deferensBulbourethral glandProstateEfferent ductulesAt birth: male developmentFigure 27.21 (5 of 5)At birth: Female developmentUterine tubeOvaryUterusUrinary bladder(moved aside)VaginaHymenVestibuleUrethraDevelopment Aspects: PubertyIn response to rising levels of gonadal hormonesReproductive organs grow to adult size and become functionalSecondary sex characteristics appear Earliest time that reproduction is possibleMenopauseHas occurred when menses have ceased for an entire yearThere is no equivalent to menopause in malesMenopauseDeclining estrogen levels Atrophy of reproductive organs and breastsIrritability and depression in someHot flashes as skin blood vessels undergo intense vasodilation Gradual thinning of the skin and bone lossIncreased total blood cholesterol levels and falling HDL