Embryology · General embryology: weeks 1 to 8
Germ-layer derivatives: ectoderm, mesoderm, endoderm !
- Topic
Every organ comes from one of the embryo's three layers; knowing which one explains many birth defects and is a fixture on exams.
Updated 2026-11-01
See it in 3D: Skin · Lens · Retina · Spinal cord · Pituitary gland · Dorsal root ganglia · Multifidus · Kidneys · Liver · Pancreas · Thyroid gland
What it is
After gastrulation the embryo has three germ layers. Ectoderm forms skin and the nervous system (with the neural crest); mesoderm forms muscle, bone, heart, blood, kidneys and gonads; endoderm forms the epithelial lining of the gut and airways and their glands. One organ often draws on several layers: gut epithelium is endodermal, but its muscle is mesodermal and its neurons come from the neural crest.
Key facts
- Ectoderm splits into surface ectoderm, neuroectoderm (neural tube) and neural crest.
- Mesoderm is ordered from medial to lateral as paraxial, intermediate and lateral plate.
- Adrenal cortex: mesoderm (coelomic epithelium); adrenal medulla: neural crest.
- Microglia: mesodermal (macrophages), unlike the other glia, which are neuroectodermal.
- Anterior pituitary: surface ectoderm (Rathke pouch); posterior pituitary: neuroectoderm.
- Facial bones and cartilage: neural crest; trunk and limb bones: mesoderm.
Germ layer and its main derivatives
| Layer | Main derivatives | Exam point |
|---|---|---|
| Surface ectoderm | Epidermis, hair, nails, sweat, sebaceous and mammary glands, lens, inner ear, anterior pituitary, enamel | Rathke pouch → anterior pituitary |
| Neuroectoderm (neural tube) | Brain, spinal cord, retina, optic nerve, posterior pituitary, pineal gland, astrocytes, oligodendrocytes, ependyma | Failed closure → neural tube defects |
| Neural crest | Dorsal root and autonomic ganglia, Schwann cells, melanocytes, adrenal medulla, C cells, pia and arachnoid, facial bones, odontoblasts, aorticopulmonary septum | Failed migration → Hirschsprung |
| Paraxial mesoderm (somites) | Vertebrae and ribs, skeletal muscle, dermis of the back | Sclerotome, myotome, dermatome |
| Intermediate mesoderm | Kidneys, ureters, gonads, genital ducts | Urogenital |
| Lateral plate mesoderm | Heart, vessels, blood, spleen, serous membranes, visceral smooth muscle, limb bones and connective tissue | Splanchnic → heart and gut; somatic → body wall |
| Endoderm | Lining of gut and airways, liver, pancreas, gallbladder, thyroid follicles, parathyroids, thymus, bladder, middle ear | Pharyngeal pouches → thymus and parathyroids |
Clinical notes
- Teratoma: a tumor with tissues from all three layers (skin, hair, teeth, gut, thyroid).
- DiGeorge syndrome: derivatives of pharyngeal pouches 3 and 4 (thymus, parathyroids) and the cardiac neural crest fail.
- Ectodermal dysplasia: skin, hair, teeth and sweat glands are affected together because they share a layer.
- VACTERL and other associations hit organs from several layers, a sign of very early injury.
Test yourself
Think of the answer, then tap the question to see it.
Which layers give rise to the adrenal medulla and the adrenal cortex?
The medulla comes from neural crest; the cortex from mesoderm (coelomic epithelium).
Which layer forms the anterior pituitary and which the posterior pituitary?
The anterior pituitary comes from surface ectoderm (Rathke pouch); the posterior pituitary from diencephalic neuroectoderm.
Which central nervous system glial cell is not neuroectodermal?
Microglia, which derive from mesoderm (the macrophage lineage).
Which layers give the epithelium and the smooth muscle of the gut wall?
The epithelium comes from endoderm; the smooth muscle and connective tissue from splanchnic lateral plate mesoderm.
Which tumor contains tissues from all three germ layers?
A teratoma.
See it in 3D
The structures of Durgical's 3D anatomy where it is found.
- Skin
- Lens
- Retina
- Spinal cord
- Pituitary gland
- Dorsal root ganglia
- Multifidus
- Kidneys
- Liver
- Pancreas
- Thyroid gland
Related
- Week 3: gastrulation and the trilaminar disc
- Neurulation and closure of the neural tube
- Neural crest cells and their derivatives
- Paraxial mesoderm and somites: sclerotome, myotome, dermatome
- Embryonic folding: head, tail and lateral folds
- Primitive gut: foregut, midgut and hindgut and their arteries
- Kidney: pronephros, mesonephros, metanephros and ascent
- Pharyngeal pouches: tonsil, thymus, parathyroids and C cells
- Adrenal gland: cortex from mesoderm, medulla from neural crest
Related conditions
Educational content on embryonic development; not a guide to prenatal diagnosis or to medicines in pregnancy and no substitute for a health professional's advice. No doses are given.
Sources: Langman's Medical Embryology, 13th ed., ch. 6: Third to Eighth Weeks: The Embryonic Period (Wolters Kluwer, 2015); Fetal development: MedlinePlus Medical Encyclopedia (MedlinePlus (U.S. National Library of Medicine), 2026); How do cells divide?: MedlinePlus Genetics (MedlinePlus (U.S. National Library of Medicine), 2026).
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Representative model, for educational purposes only.