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  <head>
    <title>085-01 Gametogenesis, fertilisation, cleavage, blastocyst formation, and implantation</title>
    <ownerName>Integrated Medical Foundations</ownerName>
  </head>
  <body>
    <outline text="Gametogenesis to implantation">
      <outline text="Timeline and germ cells">
        <outline text="Developmental age counted from fertilisation">
          <outline text="Gestational age from last menstrual period"/>
          <outline text="Gestational age about two weeks greater"/>
        </outline>
        <outline text="Primordial germ cells specified outside gonad">
          <outline text="Migrate to genital ridges"/>
          <outline text="Survival depends on somatic signals"/>
          <outline text="Imprints erased and re-established"/>
          <outline text="Failure: infertility, dysgenesis, germ-cell tumours"/>
        </outline>
      </outline>
      <outline text="Spermatogenesis">
        <outline text="Begins at puberty in seminiferous tubules"/>
        <outline text="Basal spermatogonia maintain stem cells"/>
        <outline text="Meiosis one separates homologues"/>
        <outline text="Meiosis two separates sister chromatids"/>
        <outline text="Spermiogenesis remodels without division">
          <outline text="Nucleus condenses, acrosome from Golgi"/>
          <outline text="Flagellum with mitochondria proximally"/>
        </outline>
        <outline text="Sertoli cells maintain blood-testis barrier"/>
        <outline text="Epididymal transit matures sperm"/>
        <outline text="Testosterone and follicle-stimulating hormone"/>
        <outline text="Heat, toxins, obstruction impair sperm"/>
      </outline>
      <outline text="Oogenesis and follicle">
        <outline text="Fetal arrest in prophase one">
          <outline text="Finite pool declines by atresia, ovulation"/>
        </outline>
        <outline text="Dominant follicle completes meiosis one">
          <outline text="Secondary oocyte and first polar body"/>
        </outline>
        <outline text="Meiosis two arrests at metaphase">
          <outline text="Completes only after fertilisation"/>
        </outline>
        <outline text="Unequal cytokinesis preserves cytoplasm"/>
        <outline text="Years of arrest raise aneuploidy risk"/>
        <outline text="Granulosa processes regulate meiotic arrest"/>
        <outline text="Theca makes androgen, granulosa aromatises"/>
        <outline text="Luteinising-hormone surge: ovulation, corpus luteum"/>
      </outline>
      <outline text="Fertilisation">
        <outline text="Capacitation in female tract">
          <outline text="Stepwise changes, not a single switch"/>
        </outline>
        <outline text="Occurs in ampulla of uterine tube"/>
        <outline text="Cumulus, zona binding, membrane fusion"/>
        <outline text="Fusion triggers calcium oscillations">
          <outline text="Meiosis two completes, metabolism activates"/>
        </outline>
        <outline text="Cortical reaction modifies zona">
          <outline text="Blocks polyspermy and genome imbalance"/>
        </outline>
        <outline text="Sperm gives paternal genome and centriole"/>
        <outline text="Oocyte gives cytoplasm, mitochondria, messenger RNA"/>
        <outline text="Pronuclei align on first spindle"/>
        <outline text="Many conceptions lost before recognition"/>
      </outline>
      <outline text="Cleavage and blastocyst">
        <outline text="Divisions without growth inside zona"/>
        <outline text="Compaction at about eight cells">
          <outline text="Position and polarity bias lineage"/>
        </outline>
        <outline text="Morula by about day three"/>
        <outline text="Trophectoderm mainly forms placenta"/>
        <outline text="Inner cell mass forms embryo proper"/>
        <outline text="Hatching sheds zona pellucida"/>
        <outline text="Delayed tubal transport risks ectopic">
          <outline text="Rupture with life-threatening haemorrhage"/>
        </outline>
      </outline>
      <outline text="Implantation">
        <outline text="Progesterone-dependent receptive window"/>
        <outline text="Decidualisation stores glycogen and lipid"/>
        <outline text="Apposition, adhesion, embryonic pole orientation"/>
        <outline text="Syncytiotrophoblast invades and erodes"/>
        <outline text="Cytotrophoblast is the proliferative source"/>
        <outline text="Partly embedded week one, enclosed week two"/>
        <outline text="Human chorionic gonadotropin rescues corpus luteum">
          <outline text="Trends and ultrasound beat a single value"/>
        </outline>
        <outline text="Lacunae start uteroplacental circulation"/>
        <outline text="Invasion must be controlled">
          <outline text="Too little: insufficiency, hypertensive disorders"/>
          <outline text="Too much: abnormally deep invasion"/>
        </outline>
      </outline>
      <outline text="Bilaminar disc and cavities">
        <outline text="Epiblast forms all three germ layers"/>
        <outline text="Hypoblast lines yolk-sac structures"/>
        <outline text="Amnioblasts line amnion"/>
        <outline text="Primary then secondary yolk sac"/>
        <outline text="Extraembryonic mesoderm and chorionic cavity">
          <outline text="Somatic layer lines trophoblast and amnion"/>
          <outline text="Splanchnic layer covers yolk sac"/>
        </outline>
        <outline text="Connecting stalk later forms cord"/>
        <outline text="Prechordal plate marks cranial end"/>
      </outline>
      <outline text="Assisted reproduction and synthesis">
        <outline text="Stimulation, retrieval, insemination or injection"/>
        <outline text="Genetic testing samples trophectoderm">
          <outline text="No guarantee of implantation or health"/>
        </outline>
        <outline text="Each failed transition gives a distinct outcome"/>
      </outline>
    </outline>
  </body>
</opml>
