1. Germ Cells Haploid cells
Have the ability to unite with a haploid cell of the opposite sex
Examples?
Unites to form a diploid cell

2. Embryonic Development
Development: series of orderly, precise steps that transform a zygote into a multicellular embryo ~early stage of development of multicellular organism
Includes:
1. cell division
2. cell growth
3. cell differentiation
~changing of unspecialized embryonic cells into specialized cells, tissues,& organs

3. Early Embryonic Development
Cleavage is the first major phase of embryonic development
It is the rapid succession of cell divisions (Mitotic)
It creates a multicellular embryo from the zygote
NO growth
Stages:
1. Morula~solid ball of cells
2.Blastula~ single layer of cells surrounding a fluid-filled cavity called the blastocoel
ZYGOTE
2 cells
4 cells
8 cells
Blastocoel
Many cells (solid ball)
Cross section of blastula
BLASTULA (hollow ball)

4. Embryonic Development
Gastrulation is the second major phase of embryonic development
The cells at one end of the blastula move inward,
It adds more cells to the embryo
It sorts all cells into three distinct cell layers
The embryo is transformed from the blastula into the gastrula

5. Embryonic Development
The three layers produced in gastrulation
Ectoderm, the outer layer
Endoderm, an embryonic digestive tract
Mesoderm, which partly fills the space between the ectoderm and endoderm

6. Embryonic Development
The tissues and organs of a tadpole emerge from cells of the ectoderm, mesoderm, and endoderm

7. Embryonic Development
ectoderm cells~ eventually they develop into the skin and nervous tissue of the animal
endoderm cells ~develop into the lining of the animal’s digestive tract and into organs associated with digestion.
mesoderm cells ~develop into the muscles, circulatory system, excretory system, and, in some animals, the respiratory system.

8. Embryonic Development
Organs start to form after gastrulation
Embryonic tissue layers begin to differentiate into specific tissues and organ systems

9. Tissues and organs take shape in a developing embryo as a result of
Changes in cell shape, cell migration, and programmed cell death give form to the developing animal
Tissues and organs take shape in a developing embryo as a result of
cell shape changes
cell migration
Ectoderm

10. Development programmed cell death (apoptosis) Cell suicide
Dead cell engulfed and digested by adjacent cell
programmed cell death (apoptosis)

11. Pregnancy

12. HUMAN DEVELOPMENT
The embryo and placenta take shape during the first month of pregnancy
Gestation is pregnancy
It begins at conception and continues until birth
Human gestation is 266 days (38 weeks or 9 months)
Mouse gestation is 1 month
Elephant gestation is 22 months

13. HUMAN DEVELOPMENT
Human development begins with fertilization in the oviduct
Cleavage starts
Fertilization of ovum
Ovary
Oviduct
Blastocyst (implanted
Ovulation
Endometrium
Uterus

14. HUMAN DEVELOPMENT
The embryo floats in the fluid-filled amniotic cavity,
The placenta’s chorionic villi absorb food and oxygen from the mother’s blood
Mother’s blood vessels
Placenta
Yolk sac
Amniotic cavity
Amnion
Embryo
Chorion
Chorionic villi

15. Placenta
Food & gases diffuse across blood vessels

16. HUMAN DEVELOPMENT
Embryonic development of essential organs occur in early pregnancy
The embryo may encounter risks from faults in its genes & from mother’s exposure to environmental factors
The placenta allows for a variety of substances to pass from mother to fetus
Protective antibodies
German measles virus
HIV
Drugs (prescription and nonprescription)
Alcohol
Chemicals in tobacco smoke

17. Human development from conception to birth is divided into three trimesters
First trimester
First three months
The most rapid changes occur during the first trimester
7 weeks weeks
4 weeks

18. Human development from conception to birth is divided into three trimesters
Second trimester
Increase in size of fetus
General refinement of human features
12 weeks

19. Human fetal development
The fetus just spends much of the 2nd & 3rd trimesters just growing
…and doing various flip-turns & kicks inside amniotic fluid
Week 20

20. Human fetal development
24 weeks (6 months; 2nd trimester)
fetus is covered with fine, downy hair called lanugo. Its skin is protected by a waxy material called vernix

21. Human fetal development
30 weeks (7.5 months)
umbilical cord

22. Getting crowded in there!!
32 weeks (8 months)
The fetus sleeps 90-95% of the day & sometimes experiences REM sleep, an indication of dreaming

23. Human development from conception to birth is divided into three trimesters
Third trimester
Growth and preparation for birth

24. Childbirth is hormonally induced and occurs in three stages
Hormonal changes induce birth
Labor is controlled by a positive feedback mechanism
Estrogen released from the ovaries increases the sensitivity of the uterus to oxytocin

25. Positive feedback Mechanism
Oxytocin is a powerful stimulant for the smooth muscles of the uterus
Oxytocin also stimulates the placenta to make prostoglandins that stimulate the uterine muscles to contract even more
Uterine contractions stimulate the release of more and more oxytocin and prostoglandins

26. positive feedback
Birth

27. Three stages of labor 1.Dilation of the cervix is the first stage
-Cervix reaches full dilation at 10cm
Longest stage of labor (6-12 hours or longer)
Dilation of the cervix

28. Three stages of labor Expulsion is the second stage
Period from full dilation of the cervix to delivery of the infant
Uterine contractions occur every 2-3 minutes
Mother feels urge to push down with her abdominal muscles
Infant is forced down and out of uterus and vagina within a period of 20 minutes

29. Three stages of labor
The delivery of the placenta is the final stage of labor
Usually occurs within 15 minutes after the birth of the baby

30. The end of the journey!
And you think 9 months of Biology is hard!

31. Childbirth is hormonally induced and occurs in three stages
Hormones continue to be important after the baby and placenta are delivered
Decreasing progesterone and estrogen levels allow the uterus to return to its pre-pregnancy state
Oxytocin and prolactin stimulate milk secretion

32. Reproductive technology increases our reproductive options
Hormone therapy can increase sperm or egg production
Surgery can correct blocked oviducts
Assisted reproductive technology
In vitro fertilization (IVF)
Surrogate motherhood