1. By Lauren and Jocelyn

2. Fertilization  The first step in embryonic development is fertilization (the joining of male and female gametes)  Fertilization has three parts: Penetration Activation Nuclei fusion

3. Penetration  The sperm has swam up the female reproductive tract and meets the egg  In this stage, the sperm begins to tunnel into the eggs plasma membrane

4. Activation  Once a sperm penetrates the membrane, changes occur allowing no other sperm to enter  Stimulates second meiotic division making two egg nuclei  Establishes bilateral symmetry when the cytoplasm moves around the entry spot

5. Nuclei Fusion  The sperm nucleus fuses with the haploid egg nucleus and forms the diploid nucleus of the zygote.

6. Cell Cleavage  The second step in development is the division of the zygote into a large number of small cells  The overall volume of the zygote cytoplasm does not increase  The result is a mass of about 32 cells called a morula. Each cell in the morula is called a blastomere  Eventually, a hollow ball of 500 to 2,000 cells is formed called the blastula

7. Blastula  Each cell in the blastula is in contact with neighboring cells. These interactions determine what type of cell it will become.  Just before implant in the uterus, the blastula cells can develop into 210 different types of cells in the body (embryonic stem cells)

8. Gastrulation  Gastrulation is when certain groups of cells dent inward and roll inward from the surface of the blastula  Determine the basic developmental pattern of the embryo  By the end, the cells of the embryo have arranged into three primary germ layers: Ectoderm Mesoderm Endoderm

9. Gastrulation Cont.  The ectoderm forms the epidermis, central nervous system, sense organs, and neural crest  The mesoderm forms the skeleton, muscles, blood vessels, heart, and gonads  The endoderm forms the lining of the digestive and respiratory tract, liver, and pancreas

10. Neural Crest  It is a small strip of cells formed when the neural groove is pinched off. Incorporated into the roof of the neural tube  Differentiation of the neural crest cells depend on the location For example: At the anterior end of the embryo, they merge with the anterior portion of the brain. This helps in the development of skeletal and connective tissues of the head

11. Human Development  Human development, from fertilization to birth takes an average of 266 days  Divided into three periods called trimesters

12. First Month  30 hours- first cleavage occurs  60 hours- second cleavage occurs  6-7 days- embryo reaches the uterus  2 weeks- the placenta forms, this provides nourishmentfor the embryo. Gastrulation also takes place  3 weeks- neurulation occurs. By the end of the thirdweek, over a dozen somites, which give rise to muscles,vertebrae, and connective tissues, are present and theblood vessels and gut have begun to develop. Embryois about 2 millimeters long  4 weeks- organogenesis, which is the formation of bodyorgans takes place. Eyes form, 30 somites are visibleand the arm and leg buds have begun to form. Embryois about 5 millimeters long

13. Second Month  Morphogenesis which is the formation of shape takes place  The miniature limbs of the embryo begin to take their adult shape  The arms, legs, knees, elbows, fingers, and toes can all be seen. Also, a short bony tail!!!!  The embryo has grown to about 25 millimeters and weighs about one gram  The eighth week marks the transition from embryo to fetus, all major organs of the body have been established

14. Third Month  The nervous system develops  The arms and legs begin to move  The embryo begins to show facial expressions and can suck

15. Second Trimester  Fourth month- the bones begin to enlarge and the mother can feel kicking  Fifth month- the head and body grow a fine covering of hair called lanugo, lost later in development  By the end of the fifth month- rapid heartbeat of the fetus can be heard with a stethoscope. It has grown to be about 175 millimeters in length and is 225 grams  Sixth month- the baby weighs 600 grams and is over a foot long, still cannot survive outside the uterus without special medical attention

16. Third Trimester  The weight of the fetus doubles several times  Most of the nerve tract in the brain as well as many new nerve cells are formed  The brain is not complete though. That has to happen outside the uterus because the baby would get to be too big

17. BIRTH!!  The uterus releases prostaglandins which begin the uterine contractions  Oxytocin is also released and that works with prostaglandins to to further stimulate the contractions, forcing the fetus down  When they start, contractions occur a couple times per hour and then they become more frequent  The placenta is then expelled and the umbilical cord, still attached to the baby is cut

18. Postnatal Development  The baby continues growing after birth, at a very fast rate  Babies heads are disproportionate to the rest of the body because different parts grow at different speeds

19. Diseases  Atrial septal defect- a hole between the left andthe right atrium in the heart  Cleft lip deformity- incomplete closures in thearea between the lip and the mouth  Anencephaly- part of the brain is absent

20. Why is it necessary?  It is needed to form babies. Without thissystem, there would be no way forfertilization to form into a human

21. Evolutionary Development  The primitive chordates gave rise to vertebrates, they were initially slow- moving, filter-feeding-animals  The vertebrates became fast-swimming predators  Also, some fish release sperm into the water instead of straight into the female

22. Interdependency  Female and male reproductive system Without the sperm and the egg, there would be no baby The female carries the fetus and provides the egg The male provides the sperm