Early Stages of Embryonic Development

Fertilization: The sperm travels through the fallopian tubes, meets with the egg, enters the egg, and the two nuclei fuse together. This new cell is a diploid called a Zygote.

Cleavage: The single cell begins to divide, soon to become a solid ball of cells.
The Morula is this solid ball of cells.Click HERE to see the Morula!
The Blastocyst is eventually what the Morula becomes. The Blastocyst is a HOLLOW ball of cells.

The blastocyst moves into the uterus, where it will burrow into the endometrium (the inner layer of the uterus). This is called Implantation.
Cell Differentiation occurs and the cells become specialized. Three distinct germ layers begin to form...
The Endoderm (gut liver and lungs)
The Mesoderm (skeleton, muscles heart and blood)
The Ectoderm (skin and nervous system ).
The blastula is now called a Gastrula (a hollow ball with three germ layers).

Now that pregnancy is established...

The Support Structures for the Fetus begin to form.
Site used:

The placenta is the first structure to form. It connects the mother and the fetus, which is surrounded by amniotic fluid for protection.
(pic of placenta and blood vessels) Notice how the blood vessels are CLOSE to each other. They are NOT connected.Click HERE to see an animation all about the placenta!
The umbilical cord forms next and connects the fetus to the placenta. Nutrients and oxygen from the mother are passed to the baby from the placenta through the umbilical cord. (pic of umbilical cord). Click HERE to see a simplified video about the Umbilical Cord!

Moving on to Stages of Fetal Development...

The Stages of Fetal Development are divided into Trimesters, of which there are three during pregnancy.


In the First Trimester, fertlization, cleavage, implantation and gastrulation occur. Pregnancy is established. HCG is released (HCG stands for Human Chorionic Gonadtropin. It is the hormone released that signals pregnancy). The first organ system to develop is the nervous system. The first organ to develop and work is the heart. All other systems begin to form as well. The placenta and the umbilical cord have been connected to the mother.

In the Second Trimester, accessory organs (nails, eyeleashes, and eyebrows) form. the baby is able to move, suck its thumb, kick and punch. With the help of an ultrasound, the doctors can tell the gender. The mother can feel the baby move. Soft, downy protective hair covers the skin. The baby's lungs begin to develop.
Click HERE to see the first nine weeks of pregnancy!

In the Third Trimester, the organs continue in their development. Fat deposits begin to develop (cute little fat baby!). The baby's skin develops. Light is visible, sounds are audible and the baby will react to both.

Childbirth ... This is the last stage of development and pregnancy!

Childbirth usually occurs between 38 and 42 weeks and is divided into 3 stages...

Stage 1: Dilation

The contractions trypically begin in this stage and the cervix begins to dilate. It will expand to 10 centimeters. During contractions, the baby's head pushes down on the

cervix and the amniotic sac bursts.

Stage 2: Expulsion

In this stage, the cervix is now fully dilated and contractions occur every one to two minutes. This is the stage during which the mother-to-be should be in the hospital

becuase the baby is born at the end of stage two!

Stage 3: Afterbirth

After the child is born, the placenta is expelled and the woman now has a baby! Time to celebrate!!!!!

Bibliography/Works Cited/Pictures (in order of appearance)


Other works...
The notes given out in class