Pregnancy Week 2 – The Baby’s Progress

As mentioned previously, in pregnancy week 2 the blastocyst will finally attach itself to the lining of your uterus (the endometrium) using finger-like tentacles and this will occur roughly 1 week after fertilization has taken place.

Looking at the diagram below you can see that the blastocyst is made up of 2 cell layers – an inner and an outer layer:

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Blastocyst

The Inner Layer of the blastocyst is called the embryoblast. This is responsible for the development of the embryo itself. As the embryoblast matures it will develop further into 3 embryonic germ layers (see week 1) on the body of the embryo; the internal, middle and external layers.

  • The Internal Embryonic Layer (Endoderm) – A rather primitive looking tube is formed by the internal layer that goes from the point of the mouth down to the tail and will later develop into the linings of the respiratory and digestive tract, along with the lungs, pancreas, liver, bladder, bowel and urinary tract.
  • The Middle Embryonic Layer (Mesoderm) – Leads to development of the muscles, bones, cartilage, genitalia, blood cells, blood vessels, kidneys and spleen along with the circulatory and excretory systems.
  • The External Embryonic Layer (Ectoderm) – This layer is responsible for the hair, skin, nails, enamel, eye lense, retinas, mouth and anal canals, sweat glands and the nervous system.

The diagram below distinguishes the various functions of the embryonic germ layers as mentioned:

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Embryonic Germ Layers

The Outer Layer of the blastocyst is called the Trophoblast – This is responsible for the development of the embryo’s life support system which will house the placenta. The early stages of the support system will include:

  • The Amniotic Fluid Sac in which the embryo will float
  • The Chorion which ensures that the embryo remains firmly attached to the lining of the uterus. It does this using finger-like tentacles known as Chorionic Villi.
  • A yolk sac to nourish the embryo, this will later be replaced by the placenta around week 12.

As all the cells continue to rapidly multiply each one will contain 46 chromosomes in 23 pairs. Every cell has the same 46 chromosomes except for the egg and sperm cells which only have 23 chromosomes each, allowing for both parent to donate their own genetic pattern. Every new cell created will have the same 46 chromosomes with the same genetic information as long as there are no defects and they are being copied correctly.

Your fully grown baby will be made up of billions of these cells, every single one containing the exact same genetics as the original cell created when the egg was fused together with the sperm.

So as you can see, in pregnancy week 2, the foundation of your baby’s genetic blueprint has already been mapped out and you may not even know you’re pregnant yet.

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(See 2 Weeks Pregnant – The Mother’s Progress)

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