## Embryonic Origin of Cardiac Tissue ### Germ Layer Derivation The heart develops from the **splanchnic mesoderm** (visceral mesoderm), which forms the **cardiogenic mesoderm** or cardiac crescent in the first and second weeks of development. **Key Point:** The splanchnic mesoderm gives rise to: - **Myocardium** (contractile muscle) - **Epicardium** (visceral pericardium) - **Endocardium** (inner lining) ### Three-Layer Structure The mature heart wall consists of three layers, all derived from splanchnic mesoderm: | Layer | Origin | Function | | --- | --- | --- | | Epicardium | Splanchnic mesoderm | Outer serosal layer | | Myocardium | Splanchnic mesoderm | Contractile muscle | | Endocardium | Splanchnic mesoderm | Inner endothelial lining | **High-Yield:** The parietal pericardium (fibrous and serous) is derived from **somatic mesoderm**, not splanchnic mesoderm. This distinction is frequently tested. **Clinical Pearl:** Defects in splanchnic mesoderm migration during weeks 3–8 lead to congenital heart defects such as tetralogy of Fallot, transposition of the great arteries, and septal defects. 
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