Pregnancy and DevelopmentFertilizationMechanisms of FertilizationEarly Clevages of the EmbryoThe BlastocystGastrulationDerivatives of Germ LayersImplantationNeurulation and Aminon DevelopmentDevelopment After ImplantationFunctions of the PlacentaThe Fetus (Beginning of the Ninth Week)The Effects of Pregnancy on the MotherChildbirth (Partition)Stages of LaborSites and Methods of ContraceptionDevelopmental Aspects of the Reproductive SystemPregnancy and DevelopmentFertilizationEmbryonic developmentFetal developmentChildbirthFertilizationThe oocyte is viable for 12 to 24 hours after ovulationSperm are viable for 12 to 48 hours after ejaculationSperm cells must make their way to the uterine tube for fertilization to be possibleMechanisms of FertilizationMembrane receptors on an oocyte pulls in the head of the first sperm cell to make contactThe membrane of the oocyte does not permit a second sperm head to enterThe oocyte then undergoes its second meiotic divisionFertilization occurs when the genetic material of a sperm combines with that of an oocyte to form a zygoteEarly Clevages of the EmbryoThe BlastocystBall-like circle of cellsBegins at about the 100 cell stageSecretes human chorionic gonadotropin (hCG) to produce the corpus luteum to continue producing hormonesFunctional areas of the blastocyst•Trophoblast – large fluid-filled sphere•Inner cell massGastrulationPrimary germ layers are eventually formed•Ectoderm – outside layer•Mesoderm – middle layer•Endoderm – inside layerThe late blastocyst implants in the wall of the uterus (by day 14)Derivatives of Germ LayersEctoderm•Nervous system•Epidermis of the skinEndoderm•Mucosae•GlandsMesoderm•Everything elseOrgans and structuresImplantationNeurulation and Aminon DevelopmentDevelopment After ImplantationFigure 16.16Functions of the PlacentaThe embryo is surrounded by the amnion (a fluid filled sac)An umbilical cord forms to attach the embryo to the placentaChorionic villi (projections of the blastocyst) develop•Cooperate with cells of the uterus to form the placenta•Forms a barrier between mother and embryo (blood is not exchanged)•Delivers nutrients and oxygen•Removes waste from embryonic blood•Becomes an endocrine organ (produces hormones) and takes over for the corpus luteumEstrogenProgesteroneOther hormones that maintain pregnancyThe Fetus (Beginning of the Ninth Week)All organ systems are formed by the end of the eighth weekActivities of the fetus are growth and organ specializationA stage of tremendous growth and change in appearanceThe Effects of Pregnancy on the MotherPregnancy – period from conception until birthAnatomical changes•Enlargements of the uterus•Accentuated lumbar curvature•Relaxation of the pelvic ligaments and pubic symphysis due to production of relaxinPhysiological changes•Gastrointestinal systemMorning sickness is common due to elevated progesteroneHeartburn is common because of organ crowding by the fetusConstipation is caused by declining motility of the digestive tract•Respiratory SystemNasal mucosa becomes congested and swollenVital capacity and respiratory rate increase•Cardiovascular systemBody water risesBlood volume increases by 25 to 40 percentBlood pressure and pulse increaseVaricose veins are commonChildbirth (Partition)Labor – the series of events that expel the infant from the uterusInitiation of labor•Estrogen levels rise•Uterine contractions begin•The placenta releases prostaglandins•Oxytocin is released by the pituitary•Combination of these hormones produces contractionsStages of LaborDilation•Cervix becomes dilated•Uterine contractions begin and increase•The amnion rupturesExpulsion•Infant passes through the cervix and vagina•Normal delivery is head firstPlacental stage•Delivery of the placentaSites and Methods of ContraceptionDevelopmental Aspects of the Reproductive SystemGender is determined at fertilization•Males have XY sex chromosomes•Females have XX sex chromosomes•Gonads do not begin to form until the eighth week•The determining factor for gonad differentiation is testosterone•Reproductive system organs do not function until pubertyPuberty•Puberty usually begins between ages 10 and 15•Testes form in the abdominal cavity and descend to the scrotum one month before birth•The first menses usually occurs about two years after the start of puberty•Most women reach peak reproductive ability in their late 20sMenopause occurs when ovulation and menses cease entirely•Ovaries stop functioning as endocrine organs•There is a no equivalent of menopause in males, but there is a steady decline in
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