Rb3 - Fertilization and Dev't


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Rb Group 3
Fertilization and Development
CNs 21-29

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Rb3 - Fertilization and Dev't

  2. 2. FERTILIZATION <ul><li>Initiation of biological reproduction </li></ul><ul><li>(through insemination or pollination) </li></ul><ul><li>Main Functions: </li></ul><ul><ul><li>Combine haploid sets of chromosomes from male and female  zygote </li></ul></ul><ul><ul><li>Activate egg cell </li></ul></ul><ul><ul><li>(Sperm + Egg contact = metabolic reactions) </li></ul></ul>
  3. 3. ACROSOMAL REACTION <ul><li>Release of hydrolytic enzymes to break down coating of the egg </li></ul><ul><li>Lock and Key Recognition (importance of specificity) </li></ul><ul><li>Leads to fusion of sperm + egg membranes and entry of a single sperm </li></ul><ul><li>Present in sea urchins </li></ul>
  6. 6. FUSION OF MEMBRANES Effect #1: Fast Block to Polyspermy (1/10 th sec) 1. Triggering of electrical response in egg membrane 2. Ion channel gates open 3. Na + changes membrane potential (depolarization)
  7. 7. <ul><li>Effect #2: Cortical Reaction </li></ul><ul><li>(changes in egg cytoplasm) </li></ul><ul><li>Production of IP3 </li></ul><ul><li>Increase of Ca 2+ </li></ul><ul><li>Fusion of cortical granules with membrane </li></ul><ul><li>Creation of osmotic gradient (water drawn in) </li></ul><ul><li>Swelling (pushes outer layer away from membrane) </li></ul>FUSION OF MEMBRANES … and then the outer layer will serve as the FERTILIZATION MEMBRANE. (prevents multiple fertilization)
  8. 8. CORTICAL REACTION <ul><li>Causes granules from cortex to be released via exocytosis </li></ul><ul><li>Enzymes released during this reaction hardens the fertilization membrane ( zona pellucida for humans)  Slow Block to Polyspermy </li></ul>
  9. 9. SUMMARY OF FERTILIZATION <ul><li>Contact of sperm and egg </li></ul><ul><li>Acrosomal reaction </li></ul><ul><li>Fusion of egg and sperm membranes </li></ul><ul><li>(Entry of only 1 sperm) </li></ul><ul><li>4. Fast Block to Polyspermy </li></ul><ul><li>5. Cortical Reaction </li></ul><ul><li>6. Slow Block to Polyspermy </li></ul>
  10. 10. PREGNANCY/ GESTATION <ul><li>divided into trimesters (“3 months”) </li></ul><ul><li>1 st Trimester: conception - Week 14 </li></ul><ul><li>2 nd Trimester: Week 14 – Week 28 </li></ul><ul><li>3 rd Trimester: Week 28 – Delivery/Labor/Week 40 </li></ul>
  11. 11. PREGNANCY/ GESTATION FIRST TRIMESTER <ul><li>Most profound development/rapid period of growth </li></ul><ul><li>Fetus is most susceptible to damage (disease, alcohol, etc.) </li></ul><ul><li>1. Fertilization </li></ul><ul><li>2. Cleavage - succession of rapid cell divisions </li></ul><ul><li>3. Zygote  Blastomere  Morula  Blastocyst </li></ul><ul><li>4. Implantation – attachment of blastocyst to endometrium </li></ul><ul><li>5. Start of Differentiation </li></ul>
  12. 12. <ul><li>6. Embedding of blastocyst in endometrium </li></ul><ul><li>7. Embryo directly gets nutrients from endometrium </li></ul><ul><li>8. Forming of placenta from tissues that grow out of embryo </li></ul><ul><li>9. Organogenesis </li></ul><ul><ul><li>Ectoderm- forms outer layer of gastrula </li></ul></ul><ul><ul><li>Endoderm – lines embryonic digestive tract </li></ul></ul><ul><ul><li>Mesoderm – fills space between ectoderm + endoderm </li></ul></ul>10. Secretion of hormones to signal presence and control mother’s reproductive system (ex. HCG) FIRST TRIMESTER Human Chroionic Gonadotropin (HCG) – peptide hormone produced by embryo which keeps progesterone levels up to make uterus lining thick
  13. 13. SECOND TRIMESTER <ul><li>Growth up to 30cm; Activity may be visible through abdominal wall </li></ul><ul><li>Hormone levels stabilize as HCG declines. </li></ul><ul><li>Corpus Luteum / uterine wall deteriorates. </li></ul><ul><li>Placenta secretes own progesterone to maintain pregnancy. </li></ul><ul><li>Uterus grows large enough to make pregnancy obvious. </li></ul>
  14. 14. THIRD TRIMESTER <ul><li>Growth up to 3.5kg in weight and 50cm in length </li></ul><ul><li>Fetal activity decreases </li></ul><ul><li>Uterus expansion </li></ul><ul><li>Displacement of mother’s abdominal organs </li></ul><ul><li>* Hormones to induce and regulate labor </li></ul>
  15. 15. HORMONES TO INDUCE AND REGULATE LABOR <ul><li>Highest level of estrogen  formation of oxytocin </li></ul><ul><li>Oxytocin </li></ul><ul><li>- stimulates powerful contractions through smooth muscles of the uterus </li></ul><ul><li>- stimulates placenta to secrete prostaglandins to enhance contraction </li></ul><ul><li>3. Positive Feedback : Physical and emotional stress associated with contractions stimulate release of more oxytocin and prostaglandins </li></ul>
  16. 16. MOMMY & BABY WHY DOESN’T THE MOM’S BODY REJECT THE BABY? <ul><li>Recall: Immune System </li></ul><ul><li>Self and non-self recognition </li></ul><ul><li>The baby is considered non-self because it contains half a different set of chromosomes. </li></ul><ul><li>THE PLACENTA </li></ul><ul><li>Physical barrier </li></ul><ul><li>Allows red blood cells & </li></ul><ul><li>nutrients to pass, but not </li></ul><ul><li>lymphocytes </li></ul><ul><li>T cells are restricted </li></ul>
  17. 17. MOMMY & BABY WHY DOESN’T THE MOM’S BODY REJECT THE BABY? <ul><li>FETUS </li></ul><ul><li>lymphocytic suppressor cells that inhibit response to interleukin-2 </li></ul><ul><li>masks fetus from interleukin-2’s detection of foreign objects </li></ul>
  18. 18. PARTURITION <ul><li>Birth of fetus from uterus </li></ul><ul><li>3 stages: </li></ul><ul><li>1. Dilation </li></ul><ul><li>2. Fetal Exposure </li></ul><ul><li>3. Umbilical Cord Closure and Placental Exposure </li></ul>
  19. 19. DILATION <ul><li>Thinned cervix opens up to around 3cm </li></ul><ul><li>Cervix is integrated in lower part of the uterus and on top of baby’s head </li></ul><ul><li>Full Dilation: 10 cm </li></ul><ul><li>Duration varies </li></ul><ul><li>(4-8 hours) </li></ul>
  20. 20. FETAL EXPOSURE <ul><ul><li>pressure on cervix, uterine contraction </li></ul></ul><ul><li>head must pass through narrowest part of pelvis, pubic arch and itroitus = PUSHING </li></ul><ul><li>burning sensation in labia </li></ul><ul><li>after birth of fetal head: </li></ul><ul><li>1. delivery by extension </li></ul><ul><li>2. head points to side </li></ul><ul><li>3. rotation to expose shoulders </li></ul>
  21. 21. UMBILICAL CORD CLOSURE <ul><li>After fetal exposure </li></ul><ul><li>Umbilical cord is cut and would close normally if not clamped </li></ul>
  22. 22. PLACENTAL EXPOSURE <ul><li>physiological separation done 15 – 30 mins after delivery </li></ul><ul><li>done with or without assistance (intramuscular injection of oxytocin followed by contraction) </li></ul>
  23. 23. HORMONES INVOLVED IN PARTURITION <ul><li>To make cervix ready: </li></ul><ul><ul><li>- relaxin, prostaglandin, estrogen </li></ul></ul><ul><li>b) For uterine contraction: </li></ul><ul><li>- prostaglandin, progesterone, oxytocin, specific positive feedback in oxytocin </li></ul>
  24. 24. LACTATION <ul><li>Secretion/formation of milk by the mammary glands </li></ul><ul><li>During pregnancy… </li></ul><ul><ul><li>remarkable growth in breast size due to the action of estrogen, adrenal steroids, and growth hormones which make ducts and alveoli in breast grow </li></ul></ul><ul><ul><li>prolactin, progesterone also involved </li></ul></ul>
  25. 25. START OF SECRETORY ACTIVITY <ul><li>in Milk producing unit / alveoli </li></ul><ul><li>caused by prolactin when estrogen and progesterone are withdrawn from the blood </li></ul>
  26. 26. <ul><li>Colostrum: </li></ul><ul><ul><li>also known as the ‘first milk’ of the mother </li></ul></ul><ul><ul><li>good for baby’s health </li></ul></ul><ul><ul><li>expected at pregnancy or childbirth </li></ul></ul><ul><ul><li>milk secretion increases after, usually 3 rd or 4 th day after birth </li></ul></ul><ul><ul><li>breasts are engorged, tense, tender, feel warm </li></ul></ul>START OF SECRETORY ACTIVITY
  27. 27. <ul><li>Depends on baby’s suction </li></ul><ul><li>Contractile mechanism </li></ul><ul><ul><li>moves milk fr. alveoli to ducts </li></ul></ul><ul><li>During suckling.. </li></ul><ul><ul><li>pressure in mother’s breasts </li></ul></ul><ul><ul><li>nerve impulse fr. sucking of baby </li></ul></ul><ul><ul><li>path of impulse : sensory neurons in nipples  hypothalamus in the brain  pituitary gland </li></ul></ul><ul><ul><li>Pituitary gland secretes oxytocin (for contraction of myoepithelial cells of alveoli and ducts containing milk) </li></ul></ul>EJECTION OF MILK
  28. 28. EJECTION OF MILK <ul><li>Maintenance of Breastmilk Production </li></ul><ul><ul><li>What is needed? </li></ul></ul><ul><ul><ul><li>Prolactin </li></ul></ul></ul><ul><ul><ul><li>Sucking – for removal of milk, release of prolactin </li></ul></ul></ul><ul><ul><ul><li>Milk pressure, hence periodic breast feeding </li></ul></ul></ul><ul><ul><ul><li>Continuous unless there is congestion, emotional disturbance </li></ul></ul></ul>