Germ layer
Germ layer
A Germ layer (pronounced: /dʒɜːrm leɪər/) is a primary layer of cells that forms during embryonic development. The germ layers are organized into three main categories: the ectoderm, mesoderm, and endoderm.
Etymology
The term "germ layer" is derived from the German word "Keimblätter". "Keim" translates to "germ" and "Blätter" translates to "layers". This term was first used in the 19th century to describe the primary layers of cells in an embryo.
Ectoderm
The ectoderm is the outermost germ layer. It forms from the outer layer of a gastrula, a stage in embryonic development. The ectoderm develops into the skin and nervous system, including the brain and spinal cord.
Mesoderm
The mesoderm is the middle germ layer. It forms various types of tissues and organs, including the heart, kidneys, and skeletal muscles.
Endoderm
The endoderm is the innermost germ layer. It forms the lining of the digestive tract and other internal organs like the lungs and liver.
Related terms
- Gastrulation: The process in embryonic development that forms the germ layers.
- Organogenesis: The process by which the ectoderm, endoderm, and mesoderm develop into the internal organs of the organism.
- Neurulation: The process where the ectoderm forms into the neural tube, which will later develop into the brain and spinal cord.
External links
- Medical encyclopedia article on Germ layer
- Wikipedia's article - Germ layer
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