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Organ system development
Development of the integumentary system
Development of the nervous system
Development of the renal system
Development of the reproductive system
Development of the respiratory system
Development of the axial skeleton
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There are two parts to the skeleton - the axial skeleton, which includes the bones in the skull, the vertebrae, the rib cage, and the sternum, and the appendicular skeleton, comprising of the pelvic and shoulder girdle, as well as the bones in the limbs.
During week 3, the embryo transitions from a flat organism to a more tubular creature, by folding along its longitudinal and lateral axes.
At the same time, a solid rod of mesoderm called the notochord forms on the midline of the embryo.
Above the notochord, the ectoderm invaginates to form the neural tube - an early precursor for the central nervous system.
Next, there’s the intermediate mesoderm, and finally, the lateral plate mesoderm.
The axial skeleton consists of the bones that run along the body's central axis - from the head to the tail, and it includes the skull, spine, and rib cage. The axial skeleton begins to develop very early in embryonic development, soon after gastrulation, meaning the period when the trilaminar disc with ectoderm, mesoderm, and endoderm layers is formed. Most axial skeleton bones develop from the mesoderm layer, except for the skull, which develops from the ectoderm.
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