1. FERTILIZATION AND DEVELOPMENT
From One Cell to Many
FERTILIZATION AND DEVELOPMENT

2. Fertilization and Early Development
Fertilization: Fusion of Sperm and Egg

3. The Egg
Surrounded by protective layer with binding sites for sperm attachment.
Sperm release enzymes that break down protective layer.
Once one sperm fertilizes egg, it is called a ZYGOTE.

4. Multiple Embryos
What if two eggs are released during the same menstrual cycle?
What if a single zygote splits apart and each cell begins dividing?

5. Days 1-6 Still in fallopian tube. Zygote begins mitosis.
As embryo grows, a cavity forms in the center, until embryo becomes hollow ball of cells: Blastocyst.

6. Implantation
6-7 days after fertilization, blastocyst attaches to wall of uterus and begins to grow into tissues of mother.

7. Differentiation Blastocyst begins to specialize.
Differentiation: results in development of the various types of body tissue.
Inner Cell Mass: Cluster of cells that develops within the inner cavity of the blastocyst. (body of the embryo will develop from these cells, while other cells will differentiate into protective tissue)

8. Gastrulation
Formation of three cell layers called the ectoderm, mesoderm, and endoderm.
Ectoderm and Endoderm form first. Cells that migrate from each of these layers form the mesoderm.

9. Ectoderm
Develops into skin and nervous system.

10. Mesoderm
Differentiate and form many of the body’s internal structures, including bones, muscle, blood cells, and gonads.

11. Endoderm
Forms linings of organs in the digestive system, such as the stomach, intestines, as well as in the respiratory and excretory systems.

12. Neurulation First step in development of the nervous system.
Shortly after gastrulation is complete, a block of mesodermal tissue begins to differentiate into the notochord.

13. Neurulation (cont’d_
As notochord develops, the ectoderm near the notochord thickens and forms the neural plate.
Raised edges of the neural plate form neural folds and the neural crest.
Neural folds move together and form the neural tube.

14. Neurulation

15. Neurulation (cont’d)
Spinal cord and brain will develop from the neural tube.
Cells of the neural crest migrate to other locations and become types of nerve cells, skin pigment cells, and other structures, such as the lower jaw.

16. Neurulation (cont’d)
If neural tube does not close completely, spina bifida can result.
Folic acid can prevent most cases of spina bifida.

17. The Placenta Specialized membranes form to protect and nourish embryo.
Amnion: sac filled with amniotic fluid that cushions the embryo.
Chorion: outside amnion; makes direct contact with uterine tissues.
Chorionic Villi: finger-like projections that devlop from chorion and extend into uterine lining.

18. The Placenta (cont’d) Placenta:
formed from chorionic villi and uterine lining
Connection between mother and embryo
Embryo’s organ of respiration, nourishment, and excretion
Materials diffuse from mother’s blood to baby’s without blood mixing.

20. The Placenta (cont’d) Umbilical Cord:
contains two arteries and one vein for exchange of gases
Connects embryo to placenta

21. Fetus After 8 weeks of development, the embryo is called a FETUS.
After 3 months, most of the major organs and tissues of the fetus are fully formed.
Fetus may begin to move and show signs of reflexes. (8 cm long, 28 grams) (.25 c)

22. Later Development
Although most tissues and organs have been formed after 3 months, they are not yet ready to go to work on their own.

23. Months 4-6
Tissues become more complex, specialized, and begin to function.
Heart can be heard with stethoscope
Bone replaces cartilage to form skeleton
Lanugo: soft hair grows over fetus

24. Months 7-9
During the last three months before birth, the organ systems of the fetus mature, and the fetus grows in size and mass.
Doubles in mass
Lungs and other organs undergo changes
Fetus can regulate its body temperature
CNS and lung development complete

25. Childbirth
About nine months after fertilization, factors trigger labor.
Oxytocin released from mother’s pituitary gland, triggering involuntary muscles in uterine wall to contract.
After baby is born, umbilical cord is clamped and cut.
Piece of umbilical cord eventually falls of baby leaving scar: belly button.

27. PLANARIA
COMPLETE RESEARCH PROPOSAL FORM. Use information from your prelab questions.
Search possible cuts to make on planaria for Planaria #2.
Change planaria water….use pipette to remove water. Replace water with new water from flask.
3 planaria in 3 different dishes.
Common Name: Freshwater Planarian
Scientific Name: Dugesia tigrina
Kingdom: Animalia
Phylum: Platyheminthes
Class: Turbellaria
Order: Tricladida
Family: Dugesiidae
Genus: Dugesia
Species: D. tigrina