Embryonic and Fetal Development Online Lab

Rotation

8 Weeks- All Major Body Parts are Present

Umbilical Cord Forms

Implantation

Fertilization


10 Significant Events During Embryonic / Fetal Development:

Event 1: Fertilization:
-What: Sperm penetrates the oocyte. The fusion of the oocyte with the sperm nuclei is the creation of the zygote.
- When: 1 day post ovulation.
- Why it is significant: Obviously, without this event, there would be no pregnancy / baby. I find it amazing that there is such a small period of time for fertilization to occur: ovulation usually only lasts approximately 24 hours.

Event 2: Implantation:
- What: Embryo implants itself into wall of uterus. Chorion secretes enzymes to digest away some of the tissue and blood vessels of the endometrium of the uterus.
- When: Week 2
- Why: It is important that the embryo implants in the right place, which is the uterus. The uterus sustains a healthy pregnancy. If an embryo does not implant, it results in a miscarriage. If it implants in the wrong place, like in the oviduct, it will result in an ectopic pregnancy, which is not a viable pregnancy.

Event 3: Development of Nervous System & Heart:
- What: Nervous system is first organ system to appear. Thickening appears along entire length of embryo, and invagination occurs as neural folds appear. When neural folds meet at midline, the neural tube is formed, which later develops into brain and spinal cord. Development of heart: first, there are right and left tubes, which fuse, and heart begins pumping blood.
- When: Weeks 3 & 4
- Why: These organ systems are vital to a healthy baby.

Event 4: Heartbeat can be detected.
What: The heart is fully functional, and can be seen on an ultrasound.
When: Week 4
Why: Doctors say that once a heart beat is seen, the chances of a successful pregnancy are much higher than before.

Event 5: Umbilical Cord is formed.
What: A "body stalk" connects the embryo to the chorion, and also contains the extrembryonic membrane, the allantois. Its blood vessels become the umbilical blood vessels. Head and tail then lift up, and the body stalk moves anteriorly by constriction. When this process if finished, the umbilical cord is fully formed, and it connects the developing embryo to the placenta.
When: Weeks 4-5
Why: The umbilical cord is a fetus' source of nourishment and survival.

Event 6: Brain Waves can be detected.
What: I don't really have much information for this, because I found this fact at some other website I had gone to to research the development of embryos. All I know is that the brain is functioning enough to have the waves detected.
When: Week 6
Why: I figure once the brain is fully functioning, and can be detected, it is another strong sign that the fetus is developing the way it should, and that it is strong and healthy.

Event 7: All Major Body Parts are now Present.
What: To think that a tiny little embryo (1.5 inches) has already formed all of it's major body parts!
When: Week 8
Why: Significant because it's so early in development, but all the major parts are present. (Sorry, I know it sounds repetitive, but I don't know how else to say it.)

Event 8: Ossification occurs.
What: Cartilage begins to be replaced by bone as ossification centers appear in most of the bones.
When: Month 3-4
Why: Again, a great sign of growth. When this happens, the fetus becomes "stronger", and things are developing as they should.

Event 9: Fetal Movement.
What: Although the embryo is able to move at approx. 5 weeks, fetal movement can be detected by the mother around 20 weeks for first-time mothers, and as early as 16 weeks for mothers who have had babies previously.
When: Months 4-5, depending.
Why: Fetal movement that is strong enough for a mother to feel is important because it is an indication of a healthy baby. If a mother goes a certain period of time without feeling any movement, she knows the fetus may be in distress, and can seek medical attention.

Event 10: Rotation and Birth
What: The fetus usually rotates so that its head is pointed toward the cervix. This is in preparation for birth through the birth canal. Birth- the fetus is pushed downward by contractions, the cervix stretches and the baby makes its appearance to the world.
When: Months 8-9
Why: Rotation is important because a delivery of a baby that has not rotated is much more dangerous to the fetus. The head should come out first so that the "biggest" part of the baby comes out first. When this doesn't happen, the baby can get stuck. Birth is important for obvious reasons.