Prenatal periods

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  Embryo period (weeks 3-8) prenatal development
• Fetal period (weeks 9-38): This is the period of growth and maturation. The fetus gains weight and grows rapidly. The organs and body systems continue to mature.
  

  Fetal period (weeks 9-38) prenatal development

The three germ layers also participate in the formation of extra-embryonic membranes. These membranes are structures that surround the embryo and protect it. The amnion is a fluid-filled sac that surrounds the embryo. The chorion is a membrane that surrounds the amnion and the embryo. The yolk sac is a sac that provides nutrients to the embryo. The allantois is a sac that stores waste products from the embryo.

The ectoderm gives rise to the amnion and the neural tube. The mesoderm gives rise to the chorion and the yolk sac. The endoderm gives rise to the allantois.

The extra-embryonic membranes are essential for the survival and development of the embryo. They provide the embryo with a protective environment, nutrients, and waste removal.

Here are the three major prenatal periods:

• Germinal period (weeks 1-2): This is the period of rapid cell division and differentiation. The fertilized egg implants in the lining of the uterus, and the cells begin to form the three germ layers: the ectoderm, mesoderm, and endoderm.
  

  Germinal period (weeks 1-2) prenatal development
• Embryo period (weeks 3-8): This is the period of organogenesis, when the major organs and body systems begin to form. The ectoderm gives rise to the skin, hair, nervous system, and eyes. The mesoderm gives rise to the bones, muscles, and blood vessels. The endoderm gives rise to the lining of the digestive tract, respiratory tract, and urinary tract.