12.fertilization pregnancy and_lactation


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12.fertilization pregnancy and_lactation

  1. 1. Fertilization, Pregnancy nd Lactation By Dr. D. Fisher
  2. 2. Fertilization of the Ovum <ul><li>Takes place in the fallopian tube. </li></ul><ul><li>Distally, the last 2cm remains spasmatically contracted – under the influence of estrogen for 3 days after ovulation. </li></ul><ul><li>Smooth muscle relaxes under the influence of progeterone – secreted by CL. </li></ul><ul><li>This allows the fertilized embryo to enter into the uterus. </li></ul>
  3. 3. Fertilization
  4. 4. Early Stages of Development
  5. 5. Blastocyst
  6. 6. Formation of Placenta
  7. 7. Mature Placenta and Fetus
  8. 8. Implantation of Zygote <ul><li>Initially the embryo receives its nutrition from the uterus “milk”. </li></ul><ul><li>The trophoblastic cells then secrete proteolytic enzymes which digest the stromal cells of the endometrium. </li></ul><ul><li>The trophoblastic cells then forms the placenta. </li></ul><ul><li>Blood flows from the 16 day after fertilization </li></ul><ul><li>6 weeks after fertilization – placenta takes over the fertilization of the fetus. </li></ul>
  9. 9. Early Cell Division <ul><li>Zygote divides to form 2 cells about 18-39 hours after fertilization </li></ul><ul><ul><li>2 cells divide to form 4, 8, and so on </li></ul></ul><ul><ul><li>Pluripotent: Ability to develop into wide range of tissues </li></ul></ul><ul><li>Morula </li></ul><ul><ul><li>Solid ball of 12 or more cells </li></ul></ul><ul><li>Blastocyst or hollow sphere of cells </li></ul><ul><ul><li>Implantation </li></ul></ul><ul><ul><ul><li>Burrowing into uterine wall </li></ul></ul></ul><ul><ul><li>Placenta develops from trophoblast cells </li></ul></ul>
  10. 10. Prenatal Development <ul><li>From conception to birth </li></ul><ul><ul><li>Three stages </li></ul></ul><ul><ul><ul><li>Germinal period </li></ul></ul></ul><ul><ul><ul><ul><li>First 2 weeks of development during formation of primitive germ layers </li></ul></ul></ul></ul><ul><ul><ul><li>Embryonic period </li></ul></ul></ul><ul><ul><ul><ul><li>2nd to end of 8th week, organ systems develop </li></ul></ul></ul></ul><ul><ul><ul><li>Fetal period </li></ul></ul></ul><ul><ul><ul><ul><li>Last 30 weeks, organ systems grow and mature </li></ul></ul></ul></ul><ul><li>Clinical age </li></ul><ul><ul><li>Mother’s LMP to calculate age of unborn child </li></ul></ul><ul><li>Postovulatory age </li></ul><ul><ul><li>Describes timing of developmental events </li></ul></ul><ul><ul><li>Calculated as 14 days less than clinical age </li></ul></ul>
  11. 11. The Placenta <ul><li>Foods cross the placenta by means of diffusion </li></ul><ul><li>Permeability of the placenta increases constantly – reaches a peak in the last month – sharp decrease in permeability. </li></ul>Permeability 0 8 20 40
  12. 12. Diffusion of O 2 and CO 2 <ul><li>Gradient: Fetus – 30 mmHg </li></ul><ul><li>Mother - 50 mmHg </li></ul><ul><li>Sufficient O 2 : ???? </li></ul><ul><ul><li>Fetal Hb (increase ability to carry O 2 ) </li></ul></ul><ul><ul><li>Fetal [Hb] > maternal [Hb] </li></ul></ul><ul><ul><li>Bohr effect: increase affinity for O 2 in the fetus – decrease affinity in maternal blood. </li></ul></ul><ul><li>CO 2 gradient: Fetal CO 2 – 48 mmHg </li></ul><ul><ul><ul><ul><ul><li>Maternal CO 2 – 45 mmHg </li></ul></ul></ul></ul></ul>20 mmHg gradient
  13. 13. Hormonal Control of Pregnancy <ul><li>Initially the trophoblast cells secrete Human Chorionic Gonadotrophin (HCG) </li></ul><ul><li>Functions of HCG: </li></ul><ul><ul><li>Prevents the degeneration of the corpus luteum </li></ul></ul><ul><ul><li>Stimulates the growth of the CL. </li></ul></ul><ul><ul><ul><li>Increase secretion of both estrogen and progesterone </li></ul></ul></ul><ul><ul><ul><li>Prevents mestruation </li></ul></ul></ul>
  14. 14. Hormonal Secretion of the Placenta <ul><li>Corpus luteum required until the 12 th week of pregnancy – placenta secretion of hormones takes over completely. </li></ul><ul><li>Corpus luteum degenerates. </li></ul><ul><li>During pregnancy the placenta secretes: </li></ul><ul><ul><li>HCG </li></ul></ul><ul><ul><li>Human chorionic somatomammotrophin (HCS) </li></ul></ul><ul><ul><li>Estrogen and progestrogen </li></ul></ul>
  15. 15. Functions of HCG <ul><li>Prevents copus luteum degeneration </li></ul><ul><li>Stimulates the interstitial cells of the fetal testes to secrete testosterone </li></ul><ul><ul><li>Testosterone responsible for the development of the male sex organs. </li></ul></ul>
  16. 16. Functions of HCS <ul><li>Starts to be secreted from the 5 th week </li></ul><ul><li>Increase in HCS secretion is proportional to the weight of the placenta (unterus) </li></ul><ul><li>Functions: </li></ul><ul><ul><li>Development of the breast </li></ul></ul><ul><ul><li>Growth hormone effect enhanced (X200-300) </li></ul></ul><ul><ul><li>Decrease maternal insulin sensitivty </li></ul></ul><ul><ul><ul><li>Increase [glucose] blood of the fetus </li></ul></ul></ul><ul><ul><li>Promotes release of FFA from maternal stores – alternative source of energy for her metabolism. </li></ul></ul>
  17. 17. Functions of Estrogen <ul><li>Enlargement of the uterus </li></ul><ul><li>Enlargement of the breast </li></ul><ul><li>Enlargement of the female external genitalia. </li></ul><ul><li>Relaxes various pelvic ligaments for easier birth. </li></ul>
  18. 18. Functions of Progesterone <ul><li>Initially secreted by the Corpus Luteum in moderate quantities </li></ul><ul><li>Subsequently, secreted mostly by the placenta. </li></ul><ul><li>Action: </li></ul><ul><ul><li>Development of the uterine endometrium – essential for the early nutrition of the embryo. </li></ul></ul><ul><ul><li>Decrease contractility of the gravid uterus </li></ul></ul><ul><ul><li>Contributes to the development of the ovum prior to implantation. </li></ul></ul><ul><ul><li>Prepares the breast for lactation. </li></ul></ul>
  19. 19. Fetal Growth <ul><li>Fetus </li></ul><ul><ul><li>At 60 days embryo becomes a fetus </li></ul></ul><ul><li>Fetal period </li></ul><ul><ul><li>From day 60 to birth is rapid growth </li></ul></ul><ul><ul><li>Lanugo </li></ul></ul><ul><ul><ul><li>Fine soft hair covering </li></ul></ul></ul><ul><ul><li>Vernix caseosa </li></ul></ul><ul><ul><ul><li>Waxy coat of protection </li></ul></ul></ul>
  20. 20. Parturition <ul><li>Parturition </li></ul><ul><ul><li>Process by which a baby is born </li></ul></ul><ul><li>In mother </li></ul><ul><ul><li>Estrogens overcome inhibitory influence of progesterone </li></ul></ul><ul><ul><li>Oxytocin is released </li></ul></ul><ul><li>In fetus </li></ul><ul><ul><li>Adrenal gland is enlarged prior </li></ul></ul><ul><li>Labor </li></ul><ul><ul><li>First stage </li></ul></ul><ul><ul><ul><li>Onset of regular uterine contraction until cervix dilates to fetal head diameter </li></ul></ul></ul><ul><ul><li>Second stage </li></ul></ul><ul><ul><ul><li>From maximum cervical dilation until baby exits vagina </li></ul></ul></ul><ul><ul><li>Third stage </li></ul></ul><ul><ul><ul><li>Expulsion of placenta from uterus </li></ul></ul></ul>
  21. 21. Parturition
  22. 22. Factors Influencing Parturition
  23. 23. Apgar Scores <ul><li>Assessment of newborn baby </li></ul><ul><ul><li>A ppearance, p ulse, g rimace, a ctivity, r espiratory effect </li></ul></ul><ul><ul><li>Rated on scale of 0-2, 2 denotes normal function </li></ul></ul><ul><ul><li>Total Apgar score is sum from five characteristics </li></ul></ul>
  24. 24. Parturition Physiology <ul><li>Factors which initiate: </li></ul><ul><ul><li>Ratio of estrogens/progesterone increase towards the end of pregnancy </li></ul></ul><ul><ul><li>Towards the end of term there is an increase responsiveness of the myometrium to oxytocin. </li></ul></ul><ul><ul><li>Increase fetal [oxytocin] towards end of term. </li></ul></ul><ul><ul><li>Mechanical stretch of the uterus: </li></ul></ul><ul><ul><ul><li>Increase movements of the fetus </li></ul></ul></ul><ul><ul><ul><li>Increase size of the fetus </li></ul></ul></ul><ul><ul><li>Stretch and/or irritation of cervix uterine – uterine reflex </li></ul></ul>
  25. 25. Lactation: <ul><li>Function of prolactin: </li></ul>prolactin Promotes the secretion of milk Estrogen and progesterone Birth Decrease [estrogen + progesterone Increase lactogenic effect (prolactin) Increase [milk] in the alveoli of the Breast – not the ducts!!!!!
  26. 26. Ejection of Milk: Oxytocin <ul><li>Ejection of milk: </li></ul><ul><ul><li>Neural reflex </li></ul></ul><ul><ul><li>Hormonal reflex </li></ul></ul>Suckling of breast Afferent conduction of APs spinal cord hypothalamus Prolactin secretion Oxytocin secretion Increase [milk] in the alveoli of the breast Contraction of the myoepithelial cells Ejection of milk