Bài giảng Biology - Chapter 46: Animal Reproduction

Chapter 46Animal ReproductionOverview: Doubling Up for Sexual ReproductionThe two earthworms in this picture are matingEach worm produces both sperm and eggs, which will fertilizeAnd in a few weeks, new worms will hatchFigure 46.1A population transcends finite life spansOnly by reproductionConcept 46.1: Both asexual and sexual reproduction occur in the animal kingdomAsexual reproduction is the creation of new individualsWhose genes all come from one parentSexual reproduction is the creation of offspringBy the fusion of male and female gametes to form a zygoteThe female gamete is the eggThe male gamete is the spermMechanisms of Asexual ReproductionMany invertebrates reproduce asexually by fissionThe separation of a parent into two or more individuals of approximately the same sizeFigure 46.2Also common in invertebrates is buddingIn which two new individuals arise from outgrowths of existing onesAnother type of asexual reproduction is fragmentation, whichIs the breaking of the body into several pieces, some or all of which develop into complete adultsMust be accompanied by regeneration, the regrowth of lost body partsReproductive Cycles and PatternsMost animals exhibit cycles in reproductive activityOften related to changing seasonsReproductive cyclesAre controlled by hormones and environmental cuesAnimals may reproduce exclusively asexually or sexuallyOr they may alternate between the twoSome animals reproduce by parthenogenesisA process in which an egg develops without being fertilized Among vertebrates, several genera of fishes, amphibians, and lizards, including whiptail lizardsReproduce exclusively by a complex form of parthenogenesis Figure 46.3a, bTimeOvarysizeHormonesBehaviorOvulationOvulationProgesteroneEstrogenFemale-likeMale-likeFemale-likeMale-like(a) Both lizards in this photograph are C. uniparensfemales. The one on top is playing the role of a male. Every two or three weeks during the breeding season, individuals switch sex roles.(b) The sexual behavior of C. uniparens is correlated  with the cycle of ovulation mediated by sex hormones. As blood levels of estrogen rise, the ovaries grow,  and the lizard behaves like a female. After ovulation, the estrogen level drops abruptly, and the progesterone level rises; these hormone levels  correlate with male behavior.Sexual reproduction presents a special problem for certain organismsThat seldom encounter a mateOne solution to this problem is hermaphroditismIn which each individual has both male and female reproductive systemsAnother remarkable reproductive pattern is sequential hermaphroditismIn which an individual reverses its sex during its lifetimeFigure 46.4Concept 46.2: Fertilization depends on mechanisms that help sperm meet eggs of the same speciesThe mechanisms of fertilization, the union of egg and spermPlay an important part in sexual reproductionSome species have external fertilization, in whichEggs shed by the female are fertilized by sperm in the external environmentFigure 46.5EggsOther species have internal fertilization, in whichSperm are deposited in or near the female reproductive tract, and fertilization occurs within the tractIn either situation, fertilization requires critical timingOften mediated by environmental cues, pheromones, and/or courtship behaviorInternal fertilizationRequires important behavioral interactions between male and female animalsRequires compatible copulatory organsEnsuring the Survival of OffspringAll species produce more offspring than the environment can handleBut the proportion that survives is quite smallThe embryos of many terrestrial animalsDevelop in eggs that can withstand harsh environmentsInstead of secreting a shell around the embryoMany animals retain the embryo, which develops inside the femaleMany different types of animalsExhibit parental care to ensure survival of offspringFigure 46.6Gamete Production and DeliveryTo reproduce sexuallyAnimals must have systems that produce gametesThe least complex systemsDo not even contain distinct gonads, the organs that produce gametes in most animalsThe most complex reproductive systemsContain many sets of accessory tubes and glands that carry, nourish, and protect the gametes and the developing embryosMany animals with relatively simple body plansPossess highly complex reproductive systemsFigure 46.7Male organs:Female organs:Genitalpore(Excretory pore)Seminalreceptacle(Digestive tract)Testis1Vas efferens2Sperm duct(vas deferens)3Seminalvesicle4Ovary1Oviduct2Yolk ductYolk gland3UterusMost insectsHave separate sexes with complex reproductive systemsFigure 46.8a, b(a) Male honeybee. Sperm form in the testes, pass through the sperm duct (vas deferens), and are stored in the seminal vesicle. The male ejaculates sperm along with fluidfrom the accessory glands. (Males of somespecies of insects and other arthropods haveappendages called claspers that grasp thefemale during copulation.)(b) Female honeybee. Eggs develop in the ovaries and then pass through the oviducts and into the vagina. A pair of accessory glands (only one is shown)add protective secretions to the eggs in the vagina. After mating, sperm are stored in the spermatheca, a sac connected to the vagina by a short duct.Testis1Accessorygland3Seminalvesicle Vas deferens2Penis5Ejaculatoryduct4AccessoryglandSpermathecaOvary1Vagina3OviductConcept 46.3: Reproductive organs produce and transport gametes: focus on humansFemale Reproductive AnatomyThe female external reproductive structures includeThe clitorisTwo sets of labiaThe internal organs are a pair of gonads And a system of ducts and chambers that carry gametes and house the embryo and fetusReproductive anatomy of the human femalePrepuce(Rectum)CervixVaginaBartholin’s glandVaginal openingOvaryOviductLabia majoraLabia minora(Urinary bladder)(Pubic bone)UterusUrethraShaftGlansClitorisFigure 46.9VaginaUterusCervixOvariesOviductUterine wallEndometriumFolliclesCorpus luteumOvariesThe female gonads, the ovariesLie in the abdominal cavityEach ovary Is enclosed in a tough protective capsule and contains many folliclesA follicleConsists of one egg cell surrounded by one or more layers of follicle cellsThe process of ovulationExpels an egg cell from the follicleThe remaining follicular tissue then grows within the ovaryTo form a solid mass called the corpus luteum, which secretes hormones, depending on whether or not pregnancy occursOviducts and UterusThe egg cell is released into the abdominal cavityNear the opening of the oviduct, or fallopian tubeCilia in the tubeConvey the egg to the uterusVagina and VulvaThe vagina is a thin-walled chamberThat is the repository for sperm during copulationThat serves as the birth canal through which a baby is bornThe vagina opens to the outside at the vulvaWhich includes the hymen, vestibule, labia minora, labia majora, and clitorisMammary GlandsThe mammary glands are not part of the reproductive systemBut are important to mammalian reproductionWithin the glandsSmall sacs of epithelial tissue secrete milkMale Reproductive AnatomyIn most mammalian speciesThe male’s external reproductive organs are the scrotum and penisThe internal organs Consist of the gonads, which produce sperm and hormones, and accessory glandsReproductive anatomy of the human maleFigure 46.10Erectile tissueof penisProstate gland(Urinarybladder)Bulbourethral glandVas deferensEpididymisTestisSeminalvesicle(behind bladder)UrethraScrotum Glans penisSeminal vesicle(Rectum)Vas deferensEjaculatory ductProstate glandBulbourethral gland(Urinarybladder)(Pubic bone)Erectiletissue ofpenisUrethraGlans penisPrepuceVas deferensEpididymisTestisScrotumTestesThe male gonads, or testesConsist of many highly coiled tubes surrounded by several layers of connective tissueThe tubes are seminiferous tubules Where sperm formProduction of normal spermCannot occur at the body temperatures of most mammalsThe testes of humans and many mammalsAre held outside the abdominal cavity in the scrotum, where the temperature is lower than in the abdominal cavityDuctsFrom the seminiferous tubules of a testisThe sperm pass into the coiled tubules of the epididymisDuring ejaculationSperm are propelled through the muscular vas deferens, the ejaculatory duct, and exit the penis through the urethraGlandsThree sets of accessory glandsAdd secretions to the semen, the fluid that is ejaculatedA pair of seminal vesiclesContributes about 60% of the total volume of semenThe prostate gland Secretes its products directly into the urethra through several small ductsThe bulbourethral glandSecretes a clear mucus before ejaculation that neutralizes acidic urine remaining in the urethraSemen in the Female Reproductive TractOnce in the female reproductive tractA number of processes, including contractions of the uterus, help move the sperm up the uterusPenisThe human penisIs composed of three cylinders of spongy erectile tissueDuring sexual arousalThe erectile tissue fills with blood from the arteries, causing an erectionHuman Sexual ResponseTwo types of physiological reactions predominate in both sexesVasocongestion, the filling of tissue with bloodMyotonia, increased muscle tensionThe sexual response cycle can be divided into four phasesExcitement, plateau, orgasm, and resolutionConcept 46.4: In humans and other mammals, a complex interplay of hormones regulates gametogenesisThe process of gametogenesisIs based on meiosis, but differs in females and malesOvaryPrimary germ cell in embryoDifferentiationOogoniumOogoniumin ovaryMitoticdivisionPrimary oocyte,arrested in prophaseof meiosis I(present at birth)Completion of meiosis Iand onset of meiosis IIPrimaryoocytewithinfollicleSecondary oocyte,arrested at meta-phase of meiosis IIFirstpolarbodyOvulationEntry ofsperm triggerscompletion ofmeiosis IIOvumGrowingfollicleMature follicleRupturedfollicleOvulatedsecondary oocyteCorpus luteumDegeneratingcorpus luteum2n2nnnnnFigure 46.11Oogenesis is the development of mature ovaSpermatogenesis is the production of mature spermEpididymisSeminiferous tubuleTestisCross sectionof seminiferoustubuleSertoli cellnucleusLumen ofSeminiferous tubuleSpermatogoniumPrimary spermatocyte(in prophase of meiosis I)Secondary spermatocyteEarlyspermatidsSpermatids(at two stages ofdifferentiation)Differentiation(Sertoli cells providenutrients)Meiosis IIMeiosis I completedMitotic division,producing large numbersof spermatogoniaSperm cellsAcrosomeNucleusMitochondriaNeckTailPlasma membraneHeadMidpiece2n2nnnnnnnnnnnFigure 46.12Differentiation andonset of meiosis IOogenesis differs from spermatogenesis In three major waysFirst, during the meiotic divisions of oogenesisCytokinesis is unequal, with almost all the cytoplasm monopolized by a single daughter cell, the secondary oocyteSecond, sperm are produced continuously throughout a male’s life Which is not the case in oogenesisThird, oogenesis has long “resting” periodsWhile spermatogenesis produces sperm in uninterrupted sequenceThe Reproductive Cycles of FemalesIn femalesThe secretion of hormones and the reproductive events they regulate are cyclicMenstrual Versus Estrous CyclesTwo different types of cycles occur in femalesHumans and other primates have menstrual cyclesWhile other mammals have estrous cyclesIn both cases ovulation occurs at a time in the cycleAfter the endometrium has started to thicken in preparation for implantationIn menstrual cyclesThe endometrium is shed from the uterus in a bleeding called menstruationSexual receptivity is not limited to a specific timeframeIn estrous cyclesThe endometrium is reabsorbed by the uterusSexual receptivity is limited to a “heat” periodThe Human Female Reproductive Cycle: A Closer LookThe female reproductive cycleIs one integrated cycle involving two organs, the uterus and ovariesCyclic secretion of GnRH from the hypothalamusAnd of FSH and LH from the anterior pituitary orchestrates the female reproductive cycleFive kinds of hormonesParticipate in an elaborate scheme involving both positive and negative feedbackThe reproductive cycle of the human femaleFigure 46.13a–eControl by hypothalamusInhibited by combination of estrogen and progesteroneStimulated by high levelsof estrogenInhibited by low levels ofestrogenHypothalamusAnterior pituitaryGnRHFSHLHPituitary gonadotropinsin bloodLHFSHFSH and LH stimulatefollicle to growLH surge triggersovulationOvarian cycleGrowing follicleMaturefollicleCorpusluteumDegenerating corpus luteumEstrogen secretedby growing follicle inincreasing amountsProgesterone andestrogen secretedby corpus luteumFollicular phaseLuteal phaseOvulationOvarian hormonesin bloodPeak causes LH surgeEstrogenProgesteroneEstrogen levelvery lowProgesterone and estro-gen promote thickeningof endometriumUterine (menstrual) cycleEndometriumMenstrual flow phaseProliferative phaseSecretory phase05101415202528Days1(a)(b)(c)(d)(e)3678452109The Ovarian CycleIn the ovarian cycleHormones stimulate follicle growth, which results in ovulationFollowing ovulationThe follicular tissue left behind transforms into the corpus luteumThe Uterine (Menstrual) CycleCycle after cycleThe maturation and release of egg cells from the ovary are integrated with changes in the uterusIf an embryo has not implanted in the endometrium by the end of the secretory phaseA new menstrual flow commencesMenopauseAfter about 450 cycles, human females undergo menopauseThe cessation of ovulation and menstruationHormonal Control of the Male Reproductive SystemTestosterone and other androgensAre directly responsible for the primary and secondary sex characteristics of the maleAndrogen secretion and sperm productionAre both controlled by hypothalamic and pituitary hormonesStimuli from otherareas in the brainHypothalamusGnRH from thehypothalamus reg-ulates FSH and LHrelease from theanterior pituitary.FSH acts on theSertoli cells of theseminiferoustubules, promotingspermatogenesis.LH stimulates the Leydig cells to maketestosterone, whichin turn stimulatessperm production.AnteriorpituitaryNegativefeedbackLeydig cellsmaketestosteronePrimary andsecondary sexcharacteristicsSertoli cellsSpermatogenesisTestisFigure 46.14Concept 46.5: In humans and other placental mammals, an embryo grows into a newborn in the mother’s uterusConception, Embryonic Development, and BirthIn humans and most other placental mammalsPregnancy, or gestation, is the condition of carrying one or more embryos in the uterusFertilization of an egg by a sperm, conceptionOccurs in the oviductFigure 46.15a, bOvaryUterusEndometriumFrom ovulation to implantationEndometriumInner cell massCavityBlastocystTrophoblast(a)Implantation of blastocyst(b) Ovulation releases asecondary oocyte, whichenters the oviduct.1Fertilization occurs. A sperm enters the oocyte; meiosis of the oocyte finishes; and the nuclei of the ovum and sperm fuse, producing a zygote.2Cleavage (cell division)begins in the oviductas the embryo is movedtoward the uterus by peristalsis and themovements of cilia.3 Cleavage continues. By the time the embryoreaches the uterus, it is a ball of cells.It floats in the uterus forseveral days, nourished byendometrial secretions. It becomes a blastocyst.4 The blastocyst implants in the endometriumabout 7 days after conception.5After fertilizationThe zygote undergoes cleavage and develops into a blastocyst before implantation in the endometriumFirst TrimesterHuman gestation Can be divided into three trimesters of about three months eachThe first trimesterIs the time of most radical change for both the mother and the embryoDuring its first 2 to 4 weeks of developmentThe embryo obtains nutrients directly from the endometriumMeanwhile, the outer layer of the blastocystMingles with the endometrium and eventually forms the placentaBlood from the embryoTravels to the placenta through arteries of the umbilical cord and returns via the umbilical veinPlacentaUmbilical cordChorionic villuscontaining fetalcapillariesMaternal bloodpoolsUterusFetal arterioleFetal venuleUmbilical cordMaternal portionof placentaFetal portion ofplacenta (chorion)Umbilical arteriesUmbilical veinMaternalarteriesMaternalveinsFigure 46.16The first trimester is the main period of organogenesisThe development of the body organsFigure 46.17a–c(a) 5 weeks. Limb buds, eyes, theheart, the liver, and rudimentsof all other organs have startedto develop in the embryo, whichis only about 1 cm long.(b) 14 weeks. Growth anddevelopment of the offspring,now called a fetus, continueduring the second trimester.This fetus is about 6 cm long.(c) 20 weeks. By the end of thesecond trimester (at 24 weeks),the fetus grows to about 30 cmin length.Second TrimesterDuring the second trimesterThe fetus grows and is very activeThe mother may feel fetal movementsThe uterus grows enough for the pregnancy to become obviousThird TrimesterDuring the third trimesterThe fetus continues to grow and fills the available space within the embryonic membranesA complex interplay of local regulators and hormonesInduces and regulates labor, the process by which childbirth occursEstrogenOxytocinfromovariesfrom fetusand mother'sposterior pituitaryInduces oxytocinreceptors on uterusStimulates uterusto contractStimulatesplacenta to makeProstaglandinsStimulate morecontractionsof uterusPositive feedbackFigure 46.18Birth, or parturitionIs brought about by a series of strong, rhythmic uterine contractionsThe process of labor has three stagesFigure 46.19PlacentaUmbilicalcordUterusCervixDilation of the cervixExpulsion: delivery of the infantUterusPlacenta(detaching)UmbilicalcordDelivery of the placenta123The Mother’s Immune Tolerance of the Embryo and FetusA woman’s acceptance of her “foreign” offspringIs not fully understoodMay be due to the suppression of the immune response in her uterusContraception and AbortionContraception, the deliberate prevention of pregnancyCan be achieved in a number of waysSome contraceptive methodsPrevent the release of mature eggs and sperm from gonadsPrevent fertilization by keeping sperm and egg apartPrevent implantation of an embryoMechanisms of some contraceptive methodsFigure 46.20MaleFemaleMethodEventEventMethodProduction ofviable spermProduction ofviable oocytesVasectomyCombinationbirth control pill (or injection,patch, orvaginal ring)Sperm transportdown maleduct systemOvulationAbstinenceCondomCoitusinterruptus(very highfailure rate)Spermdepositedin vaginaCapture of theoocyte by theoviductAbstinenceTubal ligationSpermicides;diaphragm;cervical cap;progestin alone(minipill, implant,or injection)Sperm movementthrough femalereproductivetractTransportof oocyte inoviductMeeting of sperm and oocytein oviductMorning-after pill (MAP)Union of sperm and eggImplantation of blastocyst in properly prepared endometriumBirthProgestin aloneModern Reproductive TechnologyRecent scientific and technological advancesHave made it possible to deal with many reproductive problemsAmniocentesis and chorionic villus samplingAre invasive techniques in which amniotic fluid or fetal cells are obtained for genetic analysisNoninvasive proceduresUsually use ultrasound imaging to detect fetal conditionFigure 46.21HeadBodyHeadBodyModern technologyCan help infertile couples by in vitro fertilization