Topic 55 - Derivatives of germ layers. Disturbances in the development – mutations
Covers how the four germ layers, ectoderm, mesoderm, endoderm and mesenchyme, give rise to tissues and organs during organogenesis. It lists the derivatives of each layer, with separate treatment of neurulation and the neural crest, and subdivides the mesoderm into paraxial, intermediate and lateral plate parts. It closes with a list of mesodermal developmental defects grouped under the VACTRL mnemonic.
Topic 55 of 59 in the MU Pleven syllabus for Cytology (Medicine, Year 1). The free AceMed note covers it in 7 sections, about 357 words (3 min of reading), with 42 flashcards.
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Topic 55 - Derivatives of germ layers. Disturbances in the development – mutations
Embryonic Period (Organogenesis)
Derivatives of Ectoderm (Neurulation)
Neural Crest Derivatives
Derivatives of Endoderm
Derivatives of Mesoderm
Disturbances in Development (Mesodermal Defects – VACTRL)
Embryonic Period (Organogenesis)
During organogenesis, four germ layers contribute to the formation of tissues and organs: ectoderm, mesoderm, endoderm, and mesenchyme.
These layers develop from ectoblast, mesoblast, and endoblast, respectively.
Derivatives of Ectoderm (Neurulation)
Surface ectoderm:
Epidermis of skin and melanocytes
Epithelium of oral cavity, anus, and nasal cavity
Epithelium of external auditory canal
Enamel of teeth
Some endocrine glands: adrenal medulla
Lens and cornea of eye, ciliary muscles
Neuroectoderm (CNS and brain):
Brain and spinal cord neurons
Oligodendrocytes, astrocytes, ependymal cells
Neural crest (PNS and nearby non-neural structures):
Autonomic nervous system
Ganglia: dorsal root, cranial, autonomic
Cranial nerves
Schwann cells
Neurulation
Formation of the neural tube from ectoderm.
Steps:
Mesodermal cells form the notochord, running along the embryo.
Notochord induces ectodermal thickening to form the neural plate.
Central neural plate cells move outwards, forming the neural groove and neural folds.
Neural folds fuse to form the neural tube.
Neural Crest Derivatives
Gives rise to PNS, cranial and autonomic ganglia, Schwann cells, melanocytes, and other non-neural structures.
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