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Mizzou MPP 3202 - Repro & devel lects1&2 11-14

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Slide 1Slide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Slide 28Slide 29Slide 30Slide 31Slide 32Slide 33Slide 34Slide 35Slide 36Slide 37Slide 38Slide 39Reproduction & Development [Ch. 26]•Sexual differentiation & gametogenesis•Hormonal control of reproduction•Procreation & pregnancy•DevelopmentSex determination in embryo [pp. 851-2]Ovum SpermSperm determines genetic sex of zygote•If zygote contains a Y chromosome: male, even if multiple X’s•If zygote gets only Y but no X lethal•X-inactivation in females: early in development, after ovaries develop, one X in each body cell inactivates, becomes Barr body— inactivation is random—some may be sperm-derived, others may be ovum-derivedSexual differentiation occurs early in development—internal organs[pp. 852-855, Fig. 26.2a]•Regardless of genetic sex, embryo has potential to become phenotypically male or female—female pattern occurs unless humoral signals are released from fetal testis•Depends upon presence of SRY gene on Y chromosome•If ♀  no SRY expression, bipotential gonads  ovaries If ♂  SRY expression elicits gonads  testes•Testes produce masculinization factors (testosterone, anti-Müller- ian hormone [AMH])•In absence of SRY, full expression of ♀ is still not default—requires other factorsCritical role of SRY gene in male determination & Development [Fig. 26.3, p. 856]Production of dihydrotestosteronerequired for development of maleexternal genitalia [Fig. 26.4, p. 856]Note that development of testis dependson presence of Y chromosome-associatedSRY expression—NOT testosterone (which is not produced until testes differentiate)Sexual Differentiation [pp. 852-6]Gametogenesis [pp. 857-8]•Males: large numbers of gametes produced continuously from stem cells, beginning at puberty and extending until senescence (age-dependent decrease in testosterone production)•Females: release only one gamete at a time from a limited pool of preformed gametes in a process that is repeated at regular monthly intervals•Gametogenesis begins in utero—mitotic divisions to increase germ cell #’s•Timing varies between male & femaleEmbryopubertyReprod.maturityEmbryoReprod.maturitypubertyMALE FEMALEFig. 26.5, p. 858]Hormonal Control of Reproduction pp. 857-860, Fig. 26.6]•GnRH release is pulsatile—necessary for optimal sensitivity to GnRH (precise mechanism unknown, may be due to modulation of pituitary sensitivity to GnRH)•LH, FSH act via feedback inhbition on GnRH release• Release of LH, FSH stimulated by low levels of gonadal steroids; when steroids ↑, usually get feedback inhibition of LH, FSH• BUT if estrogen ↑↑ can get stimulation of gonadotropin (LH) releaseHypothalamusAnt. PituitaryGonadalendocrinecellsGnRHFSHlong-loopfeedback Inhibitionor stimulationLHshort-loopfeedback inhibitionCNSInternal, environmentalstimuli (stress, nutrition, exogenous estrogens)GameteproductionGonadotropicsteroids, peptidesFemalesonlyActivins. ↑ estrogenInhibins, steroids, e.g. moderate estrogen levelsActivinsMale Reproduction—gross anatomy [pp. 860-862, Fig. 26.7a,b]Placement of testis outside abd.cavity maintains 2-3◦ C < bodytemp—necessary for sperm developmentAccessory glands (seminalVesicles, prostate, bulbo-Urethral glands)—secretefluids which lubricate tubularSystem and nutrients (e.g.fructose) to support energyusage by sperm. Fluid from seminal vesicles constitutesabout 70% to total semen volumeSite of sperm productionTestis [pp. 861-4, Fig. 26.7c-g]Site of maturation& storage of spermDuring arousal & ejaculation, contractions of circular smooth muscle aroundepidiymal duct advance sperm into vas deferens and ultimately the urethraLeydig cells—produce & secretetestosterone in response to LH;active in fetus, virtually disappearafter first 6 months of postnatal life;reappear with onset of pubertySertoli cells—regulation of spermdevelopment—secrete proteinsnecessary for sperm development(e.g. androgen-binding protein) in response to FSH & testosteroneSpermatogenesis in seminiferous tubules[p. 864-5]Hormonal Control of Spermatogenesis [pp. 864-5, Fig. 26.8]Female Reproduction—gross anatomy[pp. 866-7, Fig. 26.9aCervical canal lined with mucus-secreting cells—mucusforms protective barrierbetween vagina & uterusNormal site of implantation &development of fertilizedeggInnermost tissue layerof uterus; epithelialthickness & charactervary during menstrual cycle--cells progressthrough monthly cyclesof proliferative, secretory,and menses phases coinciding with ovarian cycleCiliary action movesegg from ovary towarduterus; dysfunction can result in infertility or ectopic pregnancyFollicular Development-ovarian cycle [p. 867-9, Fig. 26.9d,e]Postovulatory (luteal) phaseOvulationPreovulatory phaseRemnants of ruptured follicle—secreteshormones which help prepare for pregnancyIf no pregnancy,C.L. degenerates& cycle resumesFollicle developing under influence of Steadily rising levels of estrogenWhen estrogen levels peak, induces a surge of LH which induces ovulation•Corpus luteum survives for about 12 days•If no pregnancy, C.L. undergoes apoptosis, becomes inactive (corpus albicans)•As luteal cells die, secretion of estrogen and progesterone ↓•As progesterone levels ↓ blood supply to endometrium is compromised, surface epithelium begins to die•2 days after C.L. ceases fxn (14 days after ovulation), endometrium begins to slough its surface layer & menstruation begins—lasts from 3-7 days•As steroids ↓ negative feedback on hypox, pituitary, so GnRHFSH, LH ↑•Increasing FSH, LH induce start of the next ovulatory cycle (during menstrual cycle•Follicular development begins under influence of FSH•As follicles mature, FSH & LH stimulate granulosa cells and thecal cells, respectively, to produce androgens•Granulosa cells also produce AMH which limits # of follicles developing at a time by ↓’ing their sensitivity to FSH•Thecal cells synthesize androgens diffuse to granulosa cellsconvert androgens estrogensSlides 15-18: Fig. 26.12, p. 872]•At the same time, estrogen stimulates its own production by granulosa cells•Menstruation ends during early follicular phase.•In response to rising estrogen, new


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