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Development & Inheritance

Development & Inheritance. Fertilization. Sperm is viable for about 48 hrs and secondary oocyte about 24 hrs, therefore there is a 3 day window for fertilization Sperm movement toward egg enhanced by Contractions of uterus due to prostaglandins in semen

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Development & Inheritance

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  1. Development & Inheritance

  2. Fertilization • Sperm is viable for about 48 hrs and secondary oocyte about 24 hrs, therefore there is a 3 day window for fertilization • Sperm movement toward egg enhanced by • Contractions of uterus due to prostaglandins in semen • Possible chemical attractant from oocyte

  3. More Fertilization • Capacitation - increased flagellar activity • Entering sperm must penetrate corona radiata and zona pellucida (presence of glycoprotein (ZP3)) which binds sperm head and initiates release of acrosomal contents (enzymes) • Upon penetration, oocyte membrane depolarizes, triggers intracellular release of Ca+, followed by exocytosis of ZP3 inactivator and zona pellucida hardening • prevents polyspermy

  4. Even More Fertilization • Secondary oocyte completes meiosis II division, another polar body formed • Nuclei fuse becoming zygote

  5. Early Stages • Cleavage - early mitotic cell division of zygote without increase in size • First division - about 30 hrs after fertilization • After 4 days, solid mass of cells - morula • On day 5, a fluid filled cavity forms (blastocele) - blastocyst • Outer layer - trophoblast - primary fetal component for placenta

  6. Implantation • On or about the 6th day • Zona pellucida breaks down, blastocyst increases in size and finally attaches to endometrium in posterior wall • Trophoblast cells form two layers - become part of chorion • Syncytiotrophoblast - outer portion secretes enzymes to burrow into endometrium and has diffuse cell structure • Cytotrophoblast - discrete cell structure

  7. More Implantation • Trophoblast also secretes human chorionic gonadotropin (hCG) - maintains corpus luteum and its production of estrogens and progesterone • Abnormal implantation - ectopic pregnancy

  8. Embryonic Development • First 2 months - primordial organs, membranes, & placenta • Gastrulation - 2  3 germinal layers • At day 8, formation of amnion (from cytotrophoblast) and cavity • At day 12 endoderm expands to enclose yolk sac • At day 14 mesoderm appears as distinct layer • Differentiation of 3 germinal layers at embryonic disc • Provide foundation for organ structures (Table 29.1)

  9. Embryonic Membranes • Form outside of developing embryo • Yolk sac - early site of blood formation and source of cells for primitive germ (sex) cells • Amnion - grows to cover all of embryo and space containing amniotic fluid • Fluid includes maternal blood filtrate, embryonic urine and cell matter • Provides physical and temperature protection • Amniocentesis

  10. More Embryonic Membranes • Chorion - derived from trophoblast and portion of mesoderm to surround embryo (outside of amnion) • Embryo portion of placenta • Produces hCG • Allantois - important in embryonic blood formation and vessels in umbilical cord

  11. Placenta • Partial placental development (complete by month 3) • Function • Exchange of gases, nutrients and wastes • Isolation barrier to microbes (except AIDS, German measles, chicken pox, measles, poliomyelitis) • Storage of certain nutrients - carbos, proteins, calcium and iron

  12. More Placenta • Hormone production - human chorionic gonadotropin, relaxin, human chorionic somatomammotropin (hCS), corticotropin-releasing hormone (CRH) - Fig. 29.10 • hCG in urine detectable at 8 days after fertilization - pregnancy test (peaks at 9 wks) • Typical cause of morning sickness • Maternal portion derived from stratum functionalis of endometrium - decidua basalis

  13. Even More Placenta • Chorion villi extend into endometrium, ultimately with allantois derived vessels extending into regions of maternal blood (intervillous spaces) • Chorionic villi sampling (CVS) • Remains of placenta are “afterbirth”

  14. Gestational Changes • Uterine enlargement in abdomino-pelvic cavity • Increased stroke volume by 30% • Increase cardiac output by 20-30% • Increased heart rate by 10-15% • Increased blood volume by 30-50% • Increased tidal volume by 30-40% • Decreased expiratory reserve by 40% • Decreased residual capacity by 25%

  15. More Gestational Changes • Decrease in airway resistance by 36% • Increased O2 consumption by 10-20% • Pressure on stomach and bladder • Increased renal plasma flow by 35% • Increased glomerular filtration rate by 40%

  16. Labor • Labor initiated by hormonal changes • Maternal estrogen levels increase (source from altered fetal secretions) superceding the effect of progesterone which inhibits uterine contraction • Estrogen increases uterine muscle receptors for oxytocin and gap junctions • Stretching of uterine wall increases release of oxytocin from posterior pituitary (via hypothalamus)

  17. Stages of Labor • Dilation stage - from beginning of regular contractions, rupturing of amniotic sac, to full dilation of cervix • Expulsion state - from dilation to completed delivery • Placental stage - from delivery to expulsion of placenta

  18. On Your Own • Newborn physiological changes • Lactation • Basic genetics and genetic disorders

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