There is only 15% chance on a woman’s most fertile days to get pregnant. Upon ejaculation, 500 million sperms cells try to get to the egg, 6 hours later, only 1% reaches the egg. Gametes are the sex cells, which each have 23 chromosomes. When these fuse together, it becomes a zygote with 46 chromosomes.
Zygote (0-2 weeks)
In the first weeks, cell division, aka mitosis, starts. Processes that occur are;
- Cell migration means that cells move within the embryo to eventually for cells and arms etc.
- Cell differentiation means that cells reach their destination and become specific cells.
- Apoptosis; cells die. ( excess cells fall away).
2 weeks after conception, the zygote has moved to the uterus, this is a vulnerable stage that 50% of the zygotes do not survive. This is due to genetic defects. This implantation means that the zygote implants itself in the uterus well. Cells become a hollow sphere called the inner cell mass. Some parts of these become the embryo, embryonic sack or placenta. hGC is secreted, which can be tested for pregnancy.
Twins
Identical twins happen when the inner cell mass splits into two embryo’s. Genetically identical
Fraternal twins happen when 2 eggs are present and both fertilized.
Triplets happen when there are multiple eggs fertilised and one of these even possibly splits as well.
Embryo (3-8 weeks)
- The inner cells mass becomes 3 layers, ectoderm (outer), mesoderm (middle) and endoderm (internal)
- The neural tube forms à later becomes brain and spinal cord
- Support system aka placenta, umbilical cord and amniotic sac
- Organ systems develop, but this is extremely vulnerable to environmental influences (teratogens). However 15 to 20% does not survive this stage
Fetus (9 weeks until birth)
- Further development of organs and bodily systems
- Physical growth, mostly lower part of the body as the head starts growing first. This is called cephalocaudal development
- 90% get born healthy
Fact: 51.3% of the babies born are male. The chances of
.....read more
Add new contribution