1. Feb 1, 2011 AIM: How does a zygote develop from embryo to fetus to full-term baby?
DN: On slips, check true, false, or idk
Quiz FRI on Human Reproduction, Regents-style questions
HW #32 – Exam corrections due THURS Feb 3. Explain what the question wants, what you need to know, the correct answer, and your mistake.

2. Embryonic Development

3. Development of Embryo Fertilization Cleavage
Differentiation/Gastrulation
Ectoderm
Mesoderm
Endoderm

4. 1. Fertilization Combination of egg and sperm Fertilized egg = zygote
External fertilization - occurs outside the female’s body (ex: fish and amphibians)‏
Internal fertilization – occurs inside the female’s body (ex: birds and mammals)‏

5. Internal Fertilization

6. 2. Cleavage
The zygote goes through a series of rapid cell divisions (mitosis) called cleavage

7. A scanning electron micrograph of a human embryo at the eight-cell stage (day three)‏

8. 3. Gastrulation- formation of 3 cell layers

9. Parts of the Embryo
Embryo
Placenta
Amnion
Umbilical cord

10. External Development – OUTSIDE of the female's body
Egg laying
High number of eggs
Low survival rate of offspring
Offspring are less protected
In fish, amphibians, reptiles, birds

11. Internal Development – INSIDE of the female's body
Low number of eggs produced
High survival rate of offspring
Offspring are protected inside mother because the embryo grows within the mother’s body
In mammals

12. During Internal Fertilization in Placental Mammals
Egg matures in the ovary
Egg leaves ovary and enters Fallopian tube
Egg is fertilized in Fallopian tube
The fertilized egg (zygote) travels down Fallopian tube, dividing
After several divisions, the zygote has become an embryo.
The embryo attaches itself to the uterus, where it will continue to grow.

14. Feb 2, 2011 AIM: How does a developing mammalian baby receive needed substances and eliminate waste?
DN: To hand in: draw and label what you think a fetus, umbilical cord, and placenta are arranged within the uterus (womb).
Quiz FRI on Human Reproduction, Regents-style questions
HW #32 – Exam corrections due THURS Feb 3. Explain what the question wants, what you need to know, the correct answer, and your mistake.

15. Placenta

16. Placental Mammals (Internal Development)‏
Animals such as humans that feed the embryo using a placenta
Placenta - where wastes, oxygen, carbon dioxide and nutrients are exchanged between mother and embryo
The mother’s blood and the baby's blood DO NOT MIX
Gas exchange at the placenta occurs due to diffusion and active transport

17. Placental Mammals (cont’d)‏
Umbilical cord - attaches the embryo to the placenta (carries blood between embryo and placenta)‏
Uterus - site of embryonic development (baby grows here), also known as the womb

18. Human Embryo
After the zygote attaches to the wall of the uterus it is known as an embryo (~7 days)‏
Remember: the uterus has been thickening in preparation to receive the zygote
Receives nutrients from fluids in the uterus until the placenta develops
Eventually, an umbilical cord develops that connects the embryo to the placenta

19. Placenta
Materials diffuse between the mother’s blood and the embryo’s blood (their bloods do NOT mix)‏
Blood vessels in the umbilical cord carry nutrients and oxygen from mother’s blood through placenta to embryo
Can also carry drugs, toxins, and other disease organisms

21. Amnion Fluid filled sac that surrounds embryo
Filled with amniotic fluid which cushions the embryo and keeps it moist
Forms during 3rd week of pregnancy

22. Fetal Development Pregnancy lasts about 38-39 weeks!
At 5 weeks, embryo has head with eyes, nose, and mouth features
Weeks 6 and 7 - fingers and toes
During 1st two months, major organs form and heart structure begins to beat (called fetus after first 2 months)‏

23. Embryo: 4, 5, 6, 7, & 8 weeks

24. 12 Weeks

25. 14 Weeks

26. 3rd Trimester

27. Twins
Fraternal twins – develop from two separate eggs, each fertilized by different sperm
Identical twins – develop from one zygote that splits in half during early cleavage

29. Birth Begins with muscular contractions of the uterus
The amniotic sac usually breaks and releases its fluid
Over a period of hours, the contractions cause the opening of the uterus to widen
More powerful and frequent contractions push the baby out through the vagina to its new environment