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Gamete transport and fertilization

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Gamete transport and fertilization

  1. 1. Gamete Transport andGamete Transport and FertilizationFertilization
  2. 2. Semen releaseSemen release • Trace the movement of spermTrace the movement of sperm • 200 million a day200 million a day • Semen released in 3 stagesSemen released in 3 stages – Bulbourethral glandsBulbourethral glands – Seminal vesicles and prostateSeminal vesicles and prostate – Seminal vesiclesSeminal vesicles • Sperm is present in first stageSperm is present in first stage
  3. 3. Contents of SemenContents of Semen • WaterWater • MucusMucus • BuffersBuffers • Carnitine – metabolism of fatty acidsCarnitine – metabolism of fatty acids • GPC – diesterase in uterus breaks downGPC – diesterase in uterus breaks down • Enzymes for clotting and liquefactionEnzymes for clotting and liquefaction • ZincZinc • PGPG
  4. 4. Sperm StructureSperm Structure • 40 to 500 million in each ejaculate40 to 500 million in each ejaculate • 30% are abnormal30% are abnormal • Controversy over declining sperm countsControversy over declining sperm counts • StructureStructure – NeckNeck – MidpieceMidpiece – TailTail – AcrosomeAcrosome • Inner and outer membranesInner and outer membranes
  5. 5. Sperm TransportSperm Transport • 20 to 200 sperm reach the egg20 to 200 sperm reach the egg • VaginaVagina – Semen coagulation – fibrinogenaseSemen coagulation – fibrinogenase – Semen liquefactionSemen liquefaction • Many sperm are into the cervix and uterus withinMany sperm are into the cervix and uterus within minutesminutes • CervixCervix – Canal is narrow and filled with a thick mucusCanal is narrow and filled with a thick mucus – Mucus becomes more liquid before ovulationMucus becomes more liquid before ovulation – Cervical cryptsCervical crypts
  6. 6. Sperm TransportSperm Transport • UterusUterus – Climb up uterus with flagellaClimb up uterus with flagella – Oxytocin released by mechanical stimulationOxytocin released by mechanical stimulation of the cervixof the cervix – Movement of leukocytesMovement of leukocytes • OviductOviduct – Sperm wait in the isthmusSperm wait in the isthmus – Infundibulum changes orientationInfundibulum changes orientation – Cilia of fimbriaCilia of fimbria
  7. 7. Sperm CapacitationSperm Capacitation • Gains ability to fertilizeGains ability to fertilize • Modification of glycocproteins on headModification of glycocproteins on head • Thermotaxis?Thermotaxis? • Sperm last for 6 days?Sperm last for 6 days? • Egg viable or 12 to 24 hoursEgg viable or 12 to 24 hours
  8. 8. Process of fertilizationProcess of fertilization • Ovum and cumulus oophorusOvum and cumulus oophorus – Hyaluronidase breaks junctions between cellsHyaluronidase breaks junctions between cells • Zona pellucidaZona pellucida – ZP 1, 2 and 3ZP 1, 2 and 3 – Binding of sperm head to ZP3Binding of sperm head to ZP3 • Initiates the acrosomal reactionInitiates the acrosomal reaction • ZP2 receptor in inner acrosomal membraneZP2 receptor in inner acrosomal membrane maintains contactmaintains contact • Perivitelline spacePerivitelline space • Sperm attachment to membraneSperm attachment to membrane
  9. 9. Cortical reactionCortical reaction • Prevention of polyspermyPrevention of polyspermy • Ca in cytoplasm increasesCa in cytoplasm increases • Cortical granules fuse with membraneCortical granules fuse with membrane • Release contents into perivitelline spaceRelease contents into perivitelline space • Completion of 2Completion of 2ndnd meiotic divisionmeiotic division • Fusion of pronucleiFusion of pronuclei – Sperm mitochondria and tail are destroyedSperm mitochondria and tail are destroyed • Role of ubiquitinRole of ubiquitin
  10. 10. • Sex ratiosSex ratios – 105 to 100105 to 100 – Male fetuses suffer greater mortalityMale fetuses suffer greater mortality • Sex preselectionSex preselection – Microsort methodMicrosort method – Preimplantation genetic diagnosisPreimplantation genetic diagnosis • Multiple EmbryosMultiple Embryos – Fraternal and identicalFraternal and identical • ParthenogenesisParthenogenesis
  11. 11. Chromosomal AberrationsChromosomal Aberrations • Most are aborted within first trimesterMost are aborted within first trimester • Polar body fertilized – genetic mosaicPolar body fertilized – genetic mosaic – Could result in intersexCould result in intersex • Androgenesis and gynogenesisAndrogenesis and gynogenesis – Both are lethalBoth are lethal • TriplodyTriplody – PolyspermyPolyspermy • AneuploidyAneuploidy • Chromosomal tranlocationsChromosomal tranlocations

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