1. Chapter 18 Development

2. Fertilization, Cleavage, and Implantation

3. FIGURE 18.2
Early stages in the reproductive process

4. Fertilization
Sperm and egg unite: 6-24 hours after intercourse, sperm survives days in female reprod. tract
One sperm fertilizes one egg
Occurs in upper oviduct
Acrosome: contains digestive enzymes
Sperm digests thru follicle cells and zona pellucida
Sperm membrane fuses with egg membrane
Zona pellucida made impermeable to other sperm

5. FIGURE 18.3a
Fertilization. (a) Diagram showing the processes that occur before and during fertilization.

7. FIGURE 18.A
Intracytoplasmic sperm injection. An egg, held in place with a blunt-nosed pipette (right), is injected with a single sperm.

8. How many sperm normally fertilize a single egg?1 2 4
More than a million

9. Early Development
Cleavage involves: cell division without cell growth, up to about day four
Function is to restore cell size to normal (i.e. smaller than the egg cell)
Produces a “morula” – a solid ball of cells

10. FIGURE 18.8
Early stages of development in cross section

11. Blastocyst Inner cell mass cells form embryo proper
Source of embryonic stem cells
Outer (trophoblast) cells form placenta
Secrete hCG (human chorionic gonadotropin) after implantation
Extends life of corpus luteum
Basis of pregnancy test

12. Implantation
FIGURE 18.5
Implantation. About 6 days after fertilization, the blastocyst attaches to the endometrium of the uterus and begins to digest its way inward.

13. Implantation

14. The cells of the blastocyst that produce the embryo proper are called:
Zona cells
Trophoblast cells
Inner cell mass
Amnion

15. Gastrulation Cells migrate to produce a three layered embryo
Ectoderm: outermost layer
Forms nervous system, skin, etc.
Mesoderm: middle layer
Muscle, bones, blood, gonads, etc.
Endoderm: innermost layer
Viscera, gut, etc.

17. Neurulation Forms Neural Tube
The neural tube forms the CNS (brain & spinal cord)
Inductive interactions between tissues
Chemical signals influence development of nearby tissue
Ex: Neural tube induced by notochord

18. FIGURE 18.9
Formation of the central nervous system from ectoderm. Dorsal views of a human embryo (left) and corresponding cross-sectional views or parts of such views (right) are shown at 4 days during development of the brain and spinal cord.

19. FIGURE 18.9 part 1
Formation of the central nervous system from ectoderm. Dorsal views of a human embryo (left) and corresponding cross-sectional views or parts of such views (right) are shown at 4 days during development of the brain and spinal cord.

20. FIGURE 18.9 part 2
Formation of the central nervous system from ectoderm. Dorsal views of a human embryo (left) and corresponding cross-sectional views or parts of such views (right) are shown at 4 days during development of the brain and spinal cord.

21. FIGURE 18.9 part 3
Formation of the central nervous system from ectoderm. Dorsal views of a human embryo (left) and corresponding cross-sectional views or parts of such views (right) are shown at 4 days during development of the brain and spinal cord.

22. Somites: form bone & muscle
FIGURE 18.9 part 4
Formation of the central nervous system from ectoderm. Dorsal views of a human embryo (left) and corresponding cross-sectional views or parts of such views (right) are shown at 4 days during development of the brain and spinal cord.
Somites: form bone & muscle

23. The neural tube develops into:
The digestive tube
Reproductive tract
Brain and spinal cord

24. Extraembryonic Membranes and Placenta
Amnion: lines amniotic cavity, filled with amniotic fluid
Chorion: makes human chorionic gonadotropin (hCG)

25. FIGURE 18.6
Extraembryonic membranes. The amnion, yolk sac, chorion, and allantois begin to form during the second to third week after fertilization.

26. Placenta Functions Nutrient exchange with mother
Umbilical cord connects fetus to placenta
Filters nutrients, waste, and provides antibodies for fetus
No mixing of mother and fetal circulations
Endocrine organ: produces hormones
hCG
Estrogen and Progesterone

27. FIGURE 18.7
The placenta is formed from the chorion of the embryo and the endometrium of the mother. (a) The placenta begins to form at about 2 weeks (shortly after implantation) and is fully developed by about 12 weeks. (b) The internal structure of the placenta.

28. FIGURE 18.7b
The placenta is formed from the chorion of the embryo and the endometrium of the mother. (b) The internal structure of the placenta.

29. The following are functions of the placenta
Nutrient exchange with the mother
Produces hormones required for pregnancy

30. FIGURE 18.13c
The developing human. (c) An embryo about 7 weeks old.

31. FIGURE 18.13d
The developing human. (d) A fetus about 4 months old.

32. FIGURE 18.13e
The developing human. (e) A fetus about 5 months old.

34. During the first stage of labor, the cervix opens (dilates) and thins out (effaces) to allow the baby to move into the birth canal. In figures A and B, the cervix is tightly closed. In figure C, the cervix is 60 percent effaced and 1 to 2 cm dilated. In figure D, the cervix is 90 percent effaced and 4 to 5 cm dilated. The cervix must be 100 percent effaced and 10 centimeters dilated before a vaginal delivery.

35. Factors That Contribute to Labor
Estrogen: Progesterone ratio
High P promotes uterine quiescence (early pregnancy)
High E promotes uterine contractility (late pregnancy)
Oxytocin promotes uterine contractions via neuroendocrine reflex

36. Figure: 10-10
Title:
Oxytocin and childbirth.
Caption:
The steps by which oxytocin stimulates uterine contractions during childbirth.

37. Lactation During Pregnancy: After Childbirth:
High E and P during pregnancy promote breast development but inhibit milk prodn.
After Childbirth:
E & P levels plummet
Prolactin promotes milk synthesis
Oxytocin induces milk ejection via neuroendocrine reflex

38. Figure: 10-11
Title:
Oxytocin and milk ejection.
Caption:
The steps by which oxytocin stimulates milk ejection (letdown) from the mammary glands.

39. Environmental Disruptions During the Embryonic Period Cause Major Birth Defects

40. Lower limbs
FIGURE 18.16
Critical periods in development

41. Spina bifida

42. Spina bifida baby