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Pregnancy and Embryology

Pregnancy and Embryology. Conception. An oocyte can be fertilized for about 24 hours after ovulation Sperm remain viable for up to 48 hours within the female reproductive tract. Fertilization. Fertilization usually takes place in the fallopian tube.

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Pregnancy and Embryology

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  1. Pregnancy and Embryology

  2. Conception • An oocyte can be fertilized for about 24 hours after ovulation • Sperm remain viable for up to 48 hours within the female reproductive tract

  3. Fertilization

  4. Fertilization usually takes place in the fallopian tube. • The oocyte may secrete a chemical that attracts sperm. • It requires the combined action of many sperm to allow one sperm to penetrate the oocyte.

  5. After the first sperm enters the egg, changes occur which prevent other sperm from entering. • Nuclei of ovum and sperm unite to form a zygote.

  6. Twins • Dizygotic or fraternal twins occur when two separate eggs are ovulated. • Monozygotic or identical twins occur when a single egg is fertilized but dividing cells break into two groups and develop into two individuals.

  7. Zygote undergoes rapid mitotic cell division, but these do not increase the size of the zygote. They are called cleavage divisions. • Cleavage produces a solid sphere of cells called a morula. • At 4.5 to 5 days cells have developed into a hollow ball of cells called a blastocyst. • It is at this stage that it enters the uterus.

  8. Cleavage of Zygote

  9. Implantation • At about 6 days after ovulation the blastocyst implants. • It secretes enzymes which allow it to digest the endometrial wall. • This nourishes the blastocyst for about a week after implantation.

  10. Implantation anywhere outside the uterus is called an ectopic pregnancy. • It is possible for fetus to grow in the abdominal cavity, but growth inside the uterine tube causes the tube to rupture, resulting in severe bleeding.

  11. As early as 8 -12 days after fertilization, the blastocyst begins to secrete human chorionic gonadotropin or hCG. • hCG keeps the corpus luteum active until the placenta can produce estrogens and progesterone. • The presence of hCG is the basis for pregnancy tests.

  12. Inner cell mass forms two cavities: • The yolk sac • Amniotic cavity

  13. Primary germ layers • In between the yolk sac and the amniotic cavity is the embryonic disc, which gives rise to the primary germ layers: • Endoderm • Mesoderm • Ectoderm

  14. Primary Germinal Layers

  15. Gestation period • Divided into trimesters • During first trimester individual starts out as a zygote and after implantation is called an embryo. • Embryonic phase of development lasts from fertilization until the 8th week of gestation when it becomes a fetus. • By day 35 the heart is beating and eye and limb buds are present.

  16. By the end of the third month the placenta is functioning. • By month four all organ systems are formed and functioning • From then on fetal development is primarily a matter of growth.

  17. Four Month Fetus

  18. The Placenta • The chorion develops into the fetal part of the placenta. • The chorionic villi connect the fetal circulation to the placenta. • Composed of both fetal and maternal tissues

  19. Fetal Circulation

  20. Functions of the placenta: • Transfer gases • Transport nutrients • Excretion of wastes • Hormone production • estrogen and progesterone • Formation of a barrier • alcohol, steroids, narcotics, anesthetics, some antibiotics and some organisms can cross

  21. Quickening • The first movement of the fetus is felt by the mother during the fourth or fifth month of pregnancy. • By month seven the fetus is quite active. • During the last month the fetus becomes less active. • usually due to space constraints

  22. 7 Month Fetus

  23. Near the end of pregnancy the uterus undergoes Braxton-Hicks contractions. • Intermittent painless contractions which can come 10 to 20 minutes apart. • These become more frequent as gestation progresses and can be mistaken for onset of labor. • Cervix begins to thin and dilate

  24. Stage One Labor • The period from the onset of true labor contractions until the cervix is completely dilated at 10 cm. • The uterine contractions cause the cervix to dilate, and the amniotic sac may rupture. • Usually lasts 6 – 24 hours depending on the number of previous deliveries.

  25. Stage One Labor

  26. Stage Two Labor • Period from maximal cervical dilation until the birth of the baby • Lasts minutes to an hour • Contractions become more intense and frequent.

  27. Stage Two Labor

  28. Stage Three Labor • The expulsion of the placenta • Usually occurs within 15 minutes after the birth of the baby • Can range from 5 to 60 minutes.

  29. Stage 3 Labor(Bottom Right)

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