1. Development

2. Egg (female gamete) (n) + Sperm (male gamete) (n)
Fertilization
Egg (female gamete) (n) Sperm (male gamete) (n)
fertilization
Zygote (2n)
Corona radiata
Zona pellucida

3. Embryo Development
The single cell zygote must go through a vast number of changes to become a multicellular organism with differentiated cells.

4. Cleavage
A series of rapid mitotic divisions occur without growth or gene expression
The cells form a ball with a fluid filled center called a blastula
Day 1
Day 2
This forms a solid ball of cells called a morula
16 – 32 cells
Day 3
Day 4
Day 5

5. Blastula Does not have an opening Blastocoel – fluid filled center
Blastomeres – outer cells to become chorion
Inner cell mass will become the embryo
Blastula (has no ICM)
Morula
blastocoel
Indicate zygote
Blastomeres (prechorion)
Inner Cell Mass in Blastocyst

6. Human Development
Fertilization and morula formation occur in the oviduct The blastula forms as the developing embryo enters the uterus
Implantation:
Blastocyst secretes enzymes allowing it to imbed
in the uterine lining (day )

7. Implantation
Human Chorionic Gonadotropin (HGC) (secreted by the embryo) maintains the corpus luteum and production of progesterone The placenta will secrete its own progesterone later (takes over in weeks 10-12)

8. Implantation

9. Gastrulation
starts when cells on one side pulled into the embryo (invagination)
ends with the formation of a gastrula
Day 16
Blastopore (opening)
Gastrula:
three tissue layers (ectoderm mesoderm and endoderm) and a primitive digestive tract called the archenteron
invagination

10. Gastrulation ectoderm endoderm mesoderm
All tissues and organs will develop from these three layers (called germ layers). Cell fate has been determined Gene expression begins as differentiation starts.
ectoderm
endoderm
mesoderm
archenteron
blastopore

11. Gastrulation in Humans
Inner Cell Mass produces an embryonic disc Primitive streak - Site of invagination

12. Neurulation Initiating the Nervous System
Ectoderm becomes nerve chord and brain
Induction by notochord
Cell migration forms peripheral nerve tissue
Begins development of body segmentation
Somites from mesoderm form precursors to vertebrae (~ 21 days)

13. Embryonic Germ Layers
Cell differentiation begins to occur at the blastula stage. Different types of cells use (express) different parts of the DNA code

14. Extra Embryonic Tissues

15. Site of exchange of nutrients and waste
Placenta
Site of exchange of nutrients and waste
Embryo part forms from chorion
Maternal part forms from uterine tissues
Blood of mother and embryo or fetus never mix

16. Stretches between placenta and fetus
Umbilical Cord
Stretches between placenta and fetus
Carries oxygen and nutrients to fetus
Carries carbon dioxide and wastes to placenta

17. Embryo Development Fifth Week
Limb buds form, head (brain) enlarges, sensory organs noticeable

18. Embryo Development

19. Embryo Development
Human
Pig
Chick
Fish

20. Fetal Development Embryonic stages occur in the first eight weeks.
All organs are initiated in the embryonic stage
Fetal development occurs from week nine through week 40
Marked by a great increase in size and weight

21. 12 – 16 weeks

22. Figure 29.24
24 weeks

23. Parturition Three stages:
1. Expansion of the cervix Delivery of the fetus
3. Expulsion of the placenta (“afterbirth”)