1. Fertilization
Sperm are ejaculated from the penis into the vagina just below the cervix and then swim through the uterus into the Fallopian tubes and they join with an egg = internal fertilization
The egg is surrounded by a thick protective layer that contains sperm binding sites
When a sperm binds to the egg, enzymes in a sac on the head of the sperm (acrosome) break through the protective layer of the egg
The sperm enters the egg and their nuclei rupture and join
A fertilized egg = zygote
The zygote begins to divide by mitosis forming a ball of cells
that attaches itself to the wall of the uterus

2. Fertilization and Implantaton
Section 39-4
Uterine wall
Blastocyst
Morula
4 cells
2 cells
Zygote
Ovary
Fallopian tube
Day 3
Day 2
Day 1
Day 4
Fertilization
Day 0
Day 7
Implantation of blastocyst
Egg released by ovary

3. Early Development
Cleavage is the first major phase of embryonic development, it occurs in the fallopian tubes
It is the rapid succession of cell divisions (Mitotic)
It creates a multicellular embryo from the zygote
NO growth occurs cells divide in given space
After 4 days, the embryo is a ball of about 50 cells = morula
As the morula grows, a hollow fluid-filled cavity forms in the center when this occurs it is now called a blastocyst
After 6-7 days, the blastocyst attaches itself to the wall of the uterus by secreting enzymes that digest a path into the soft tissue = implantation

4. Cleavage and Blastocyst Formation
Figure 20-2

5. Embryonic Development
Gastrulation is the second major phase of embryonic development
The cells at one end of the blastula move inward
Organs start to form after gastrulation
Embryonic tissue layers begin to differentiate into specific tissues and organ systems

6. Gastrulation
3 layers = primary germ layers because all organs and tissue will be formed from them
Ectoderm (outer) – becomes skin and nerves
Mesoderm (middle) – becomes everything else
Endoderm (inner) - becomes digestive, excretory, and respiratory systems
Membranes develop that surround, protect, and nourish the developing embryo = amnion and chorion

9. Structures of early development

10. Placenta
After 3 weeks of development, the nervous and digestive systems have begun to form
The chorion has grown into the placenta
Placenta = connection between mother and developing embryo supplying nutrients and oxygen and eliminating carbon dioxide and other wastes (respiration, nourishment, and excretion)
The placenta separates the mother’s and embryo’s blood, but gases, food and wastes can diffuse across it
After 8 weeks of development, embryo = fetus
After 3 months of development, fetus has umbilical cord connecting fetus to placenta, most organs are fully formed (including muscles) and the fetus can reflex
Amnion has grown into amniotic sac , filled with amniotic fluid that cushions and protects developing fetus

12. Later Development
After 6 months of development, tissues are more complex and specialized, skeleton formed, heartbeat strengthened, soft hair grows over skin, and fetus continues to increase in mass
The fetus may be able to survive outside the uterus with life-supporting equipment
Last 3 months of development increase the fetus’ chances of survival
The fetus doubles in mass, lungs and other organs change to prepare for life outside uterus

13. Critical Times…

14. Childbirth
After about 9 months of development, the fetus if ready for birth
Oxytocin from the pituitary gland affects large involuntary muscles in the uterine wall, stimulating contractions = labor
Cervix expands until large enough to pass the head of the baby
Amniotic sac breaks and fluid rushes out of the vagina = “water-breaking”
Uterine contractions become stronger and more frequent, forcing baby out through the vagina
The baby cries or coughs when outside the body, riding the lungs of fluid, so breathing can begin immediately
The blood supply through the umbilical cord dries up and it is cut leaving a scar on the baby (navel/belly-button)
After birth, the placenta and empty amniotic sac are expelled by a final series of uterine contractions called the afterbirth

15. Labor Dilation Stage Begins with onset of true labor Cervix dilates
Fetus begins to shift toward cervical canal
Highly variable in length, but typically lasts over 8 hours
Frequency of contractions steadily increases
Amnionic membrane ruptures (water breaks)

16. Labor

17. Labor Expulsion Stage Delivery Begins as cervix completes dilation
Contractions reach maximum intensity
Continues until fetus has emerged from vagina:
Typically less than 2 hours
Delivery
Arrival of newborn infant into outside world

18. Labor
Figure 20-11

19. Labor
Placental Stage
Muscle tension builds in walls of partially empty uterus
Tears connections between endometrium and placenta
Ends within an hour of delivery with ejection of placenta, or afterbirth
Accompanied by a loss of blood

20. Labor
Figure 20-11

21. After Childbirth
The baby begins to lead an independent existence (respiration, excretion, maintaining homeostasis)
The mother’s pituitary gland secretes the hormone prolactin, which stimulates the production of milk in the breast tissue
Breast milk contains all of the nutrients the baby needs for growth and development during the first few months of life

22. Multiple Births?
Fraternal twins = when 2 eggs are released and fertilized by 2 sperm during the same cycle
Not identical because different eggs fertilized by different sperm
Identical twins = when 1 zygote splits producing 2 embryos
Identical because contain genetic information from same egg and same sperm

23. Multiple Births Conjoined Twins Siamese twins
Genetically identical twins
Occurs when splitting of blastomeres or of embryonic disc is not completed

24. Reproductive Technologies
have made it possible to:
fertilize and egg outside the female body
called In vitro fertilization. 
introduce semen inside the female body without sex
called artificial insemination.
Implant a fertilized egg into the uterus :
also done by artificial insemination.
Hormone therapy: provide female hormones to woman who can no longer make them. Risky.