1. Fertilization and Development

2. Fertilization
Until this point, we have assumed that the released egg was not fertilized by a sperm
However, if sperm are in the Fallopian tube, there is a chance that the egg will become fertilized
Sperm attaches by finding binding sites on egg
Layer containing sites then dissolves, removing possibility of polyspermy

3. Two haploid nuclei merge to form diploid zygote
Will begin to develop even before it reaches the uterus

4. Early Development Divided into three stages: Implantation Gastrulation
Neurulation

5. Implantation
After fertilization, zygote goes through a series of mitotic divisions, with very little time between each
Reaches around 64 cells (solid ball), called a morula
Morula is not much larger than original single cell
Begins to hallow out, becomes blatocyst

6. Blastocyst will secrete digestive enzymes to burrow into uterine lining (recall it should be thickest now) about one week after fertilization
This is the implantation
Can cause spotting for the female

7. Blastocyst cells can begin to differentiate

8. Cluster of cells form inside blastocyst
This inner cell mass will become the embryo
Trophoblast surrounding this will become the placenta and umbilical cord

9. Gastrulation ICM differentiates into three layers
Ecotoderm – skin and nervous system
Endoderm – lining of digestive track and internal organs
Mesoderm – inner tissue and organs

10. Primitive streak is where cell grow out of to form mesoderm
Amniotic cavity
Primitive streak
Mesoderm
Ectoderm
Endoderm
Primitive streak is where cell grow out of to form mesoderm

11. Neurulation Formation of the CNS
Block of mesoderm differentiates into notochord – eventually becoming the spine

12. As the notochord develops, the neural groove changes shape, producing neural folds
Neural crest
Neural fold
Notochord

13. Gradually, these folds move together to create a neural tube from which the spinal cord and the nervous system develop
Neural tube
Neural crest
Ectoderm
Notochord

14. Extraembryonic Membranes
Trophoblast and mesoderm continue to develop, forming two membranes called amnion and the chorion
The amnion develops into a fluid-filled amniotic sac, which cushions and protects the developing embryo
Chorion forms finger-like projections, connecting mother to fetus

15. Amniotic sac
Placenta
Umbilical cord
Uterus
Amnion
Fetus

16. The chorionic villi and uterine lining form the placenta
Maternal portion of placenta
Fetal portion of placenta
Chorionic villus
Amnion
Umbilical cord
Maternal artery
Umbilical arteries
Maternal vein
Umbilical vein
The chorionic villi and uterine lining form the placenta

17. The Placenta
Serves as embryo’s organ for respiration, nourishment, and excretion
Protects fetus from many, but not all, harmful substances
Viruses such as HIV and substances such as alcohol pass through

18. First Trimester Embryo becomes fetus at eight weeks
Most major organs and tissues formed
Umbilical chord develops, connects baby to mother

19. Second Trimester The heart can be heard with a stethoscope
Bone replaces cartilage that forms the early skeleton
A layer of soft hair grows over the fetus’s skin
The fetus grows and the mother can feel it moving

20. Third Trimester The fetus doubles in mass
It can now regulate its body temperature
The central nervous system and lungs completely develop
Gestation

21. Childbirth Mother’s pituitary gland secretes oxytocin
Causes rhythmic, involuntary contractions of muscles around uterine wall
This is known as labour
Amniotic sac will break (water breaking)
Opening to cervix expands, convulsions push baby out through vagina
The Birth Video!