1. 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

2. 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)

3. 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

4. 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

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

6. 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.

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

8. 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

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

10. Embryonic induction initiates organ formation
Induction is the mechanism by which one group of cells influences the development of tissues and organs from ectoderm, endoderm, and mesoderm
Adjacent cells and cell layers use chemical signals to influence differentiation
Chemical signals turn on a set of genes whose expression makes the receiving cells differentiate into a specific tissue

11. Pattern formation organizes the animal body
Pattern formation is the emergence of a body form with structures in their correct relative positions
It involves the response of genes to spatial variations of chemicals in the embryo

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 Cleavage produces a blastocyst
A blastocyst is a fluid-filled cavity
The inner cells of the blastocyst form the baby
The outer cells form the embryo trophoblast
ENDOMETRIUM
ENDOMETRIUM
Inner cell mass
Cavity
Trophoblast

15. HUMAN DEVELOPMENT
The trophoblast secretes enzymes to enable the blastocyst to implant in the uterine wall
ENDOMETRIUM
Blood vessel (maternal
Future embryo
Multiplying cells of trophoblast
Future yolk sac
Trophoblast
UTERINE CAVITY

16. HUMAN DEVELOPMENT
Gastrulation occurs and organs develop from the ectoderm, endoderm, and mesoderm
Amnion
Mesoderm cells
Chorion
Yolk sac

17. HUMAN DEVELOPMENT Meanwhile, the four embryonic membranes develop
Amnion~fluid filled sac for protection
Chorion ~ will form the embryo’s part of the placenta
Yolk sac ~ produces first blood cells &germ cells
Allantois ~ will form the umbilical cord (ropelike structure that attaches embryo to uterus)
Chorion
Amnion
Allantois
Yolk sac

18. 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

19. Placenta
Food & gases diffuse across blood vessels

20. 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

21. 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

22. 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

23. 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

24. 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

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

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

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

28. 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

29. 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

30. positive feedback
Birth

31. 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

32. 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

33. 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

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

35. 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

36. 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