Germ layer

Germ layer is a primary layer of cells that form during embryogenesis. The three germ layers in vertebrates are particularly among the most fundamental topics in embryology. These layers are the ectoderm, mesoderm, and endoderm.

Overview

Germ layers start to form after the fertilization of an egg by a sperm cell. Once the zygote divides, it becomes a blastula, which is a hollow ball of cells. The blastula undergoes gastrulation, forming the three germ layers: ectoderm, mesoderm, and endoderm.

Ectoderm

The ectoderm forms the outermost layer and gives rise to the central nervous system, the peripheral nervous system, and the epidermis with its associated structures including hair and nails.

Mesoderm

The mesoderm forms the middle layer and gives rise to the muscles, the circulatory and excretory systems, the reproductive system, dermis and other connective tissues of the body.

Endoderm

The endoderm forms the innermost layer and gives rise to the lining of the digestive tract and its associated structures, the respiratory system, the urinary bladder, and the digestive organs.

See also

• Embryogenesis
• Gastrulation
• Organogenesis

References

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External links

• Germ layer at WikiMD

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Germ layer

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  Historical illustration of germ layers by Remak, 1855
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  Diagram of gastrulation process
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  Endoderm layer illustration
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  Mesoderm layer illustration
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  Ectoderm layer illustration
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  Teratoma showing differentiation of germ layers