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| Rapid mitotic divisions in early embryonic development. These lead to an increase in cell number without a corresponding growth in cell protoplasm (i.e., the total volume of cytoplasm remains constant.) This results in progressively smaller cells, with an increasing ratio of nuclear-to-cytoplasmic material. This converts the fertilized egg into a blastula in 3 stages. |
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| A hollow sphere of cells during embryonic development that implants in the uterus. |
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| Blastula is transformed into this 3 layer structure after it is implanted in the uterus. The 3 layers are Ectoderm, Endoderm, and Mesoderm. |
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| Layer of the Gastrula that develops into the epidermis, hair, nails, epithelium of the nose, mouth, anal canal, lens of the eye, retina, and nervous system. |
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| Layer of the Gastrula that develops into the epithelial linings of the digestive and respiratory tracts, parts of the liver, pancreas, thyroid, and bladder lining. |
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| Layer of the Gastrula that develops into musculoskeletal system, circulatory system, excretory system, gonads, connective tissue throughout the body, and portions of the digestive and respiratory organs. |
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| Thin though membrane that contains the amniotic fluid which acts as a shock absorber for external and localized pressure on the embryo. |
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| During this time the major organs develop. The heart begins to beat and the eyes, gonads, limbs, and liver are formed. The cartilaginous skeleton turns into bone and the embryo is now a fetus. |
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| During this time the fetus grows from 9 cm to 30 cm. The toes and fingers elongate and the face takes a human shape. |
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| The 2/3 is characterized by continued rapid growth and further brain development. During the last 1/3 growth rate slows and fetus becomes less active. Also antibodies are transported by highly selective active transport from the mother to the fetus. |
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