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Chapter 6

PSY354H5 Chapter 6: Sexual Development

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Brett Beston

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NotesFromReadingCHAPTER6SEXUALDEVELOPMENTPGS152189FERTILIZATION IS THE FUSION OF ONE SPERM WITH ONE OVUMFertilization The entry of a sperm into an ovum thus transforming the ovum into a genetically unique diploid organism capable of development conceptus This usually occurs if sperm are present in the oviduct at the time of ovulation or arrive within 24 hours afterwardZygote A cell formed by the fusion of gametes a fertilized ovumIf fertilization does not occur within about 24 hours of ovulation the ovum dies and the luteal phase continues on to menstruationBefore fertilization can take place the sperm must undergo two important processesoCapacitation Chemical change in the surface of a sperm within the female reproductive tract that allows it to swim more forcefully and respond to the presence of the ovumoAcrosome Reaction The opening of a sperms acrosome releasing enzymes necessary for penetration of the zona pellucida of the ovumOnce capacitated a single sperm can live only a few hours so it must find an ovum or die Bourgeonal An aromatic aldehyde that attracts spermatozoa to the ovumZona Pellucida Capsule surrounding an ovum that must be penetrated by the fertilizing spermThe sperms acrosome fuses with its outer membrane exposing receptors that bind to the zona pellucida and releasing proteindigesting enzymes that clear a path through the zona pellucida for the sperm to reach ovums plasma membrane When the sperm fuses with the plasma membrane the concentration of free calcium ions within the ovum increases briefly This triggers the release of enzymes from the ovum changing the physical properties of zona pellucida making it difficult for other sperm to pass throughWithin the next few minutes the ovum completes its second meiotic division having the second polar body the other daughter cell inherits most of the cytoplasmoSecond Polar Body A small body containing the chromosomes discarded during the second meiotic division of an ovumThe ovum now contains two Pronuclei A nucleus containing a haploid set of chromosomes derived from a sperm or ovum The two pronuclei undergo a round of DNA replication so that each chromosome now consists of two identical chromatidsThe pronuclear membranes break down a mitotic spindle forms the chromatids are pulled apart and the cell divides This is the first mitotic cell division of the new organismEach daughter cell inherits one set of chromosomes from each of the two pronuclei so these two cells and all their descendants are diploidConception Fertilization of the ovum implantation or the secure establishment of pregnancy The Conceptus Implants in the Uterine WallConceptus The developing organism from the 2cell stage onward including both embryonic and extraembryonic tissuesEmbryois commonly used to refer to a conceptus from the 2cell stage onward especially in thecontext of in vitro fertilization The conceptus remains in the oviduct for about 3 days after ovulation during which time it undergoes few more rounds of cell division The conceptus remains confined within the original zona pellucidaAt the 4 or 8cell stage the conceptuss genes become active for the first timeMorula Conceptus when it consists of about 16 to 32 cells arranged in a compact spherical thmass Around 4 day the conceptus is swept into the uterus by action of cilia lining the oviduct The conceptusnow containing about 32 cellsdevelops a central fluidfilled cavity and the conceptus is now referred to as blastocyst oBlastocyst A conceptus shortly before implantation when it takes the form of a sphere of cells with a central cavity
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