Differentiation of the Germ Layers
| Germ Layer | Adult Derivatives | |||
| Ectoderm | Surface ectoderm | Epidermis and its derivatives (hairs, nails, sweat and sebaceous glands); Mammary glands Epithelial lining of the oral cavity structures, ameloblasts, salivary glands; Lens of eye; Adenohypophysis; Epithelial lining of external auditory meatus; utricle, semicircular ducts Olfactory placode; Epithelial lining of lower anal canal | ||
| Neuroectoderm | Nerve tube | CNS (all neurons and glial cells); Retina; Pineal gland | ||
| Nerve crest | PNS end many other structures (table) | |||
| Mesoderm | Paraxial (SOMITES) | Dermatome | Skin dermis | |
| Myotome | Skeletal muscles of trunk, limbs, head and neck; extraocular muscles; intrinsic muscles of tongue | |||
| sclerotome | Vertebrae and ribs; cranial bone | |||
| Intermediate (Nephrogonotome) | Kidneys Reproductive system organs | |||
| Lateral (splanchnotome) | Serous membranes of body cavities (mesothelium) Carddiogenic mesoderm (splanchnic mesoderm) → heart Suprarenal cortex cells | |||
| Mesenchyme | Blood, lymph, connective tissue, smooth muscle cells, blood vessels, endocardium | |||
| Endoderm | Epithelial lining of the gastrointestinal tract, the liver, the pancreas, the gall bladder; epithelial lining of the respiratory system (trachea, bronchi, lungs), the thymus stroma, the thyroid and the parathyroid glands endocrine cells; epithelial lining of the urinary bladder, the female urethra and most of the male urethra | |||
DIAGRAM of CONSECUTIVE STAGES of HUMAN EMBRYOGENESIS
1- uterine mucosa; 2- epithelium; 3- connective tissue; 4- trophoblast;
5- embryoblast; 6- amniotic vesicle (ectoderm material); 7- entoderm material;
8- extraembryonic mesoderm; 9- extraembryonic mesenchyme;
10- differentiation of trophoblast; 11- yolk sac; 12-amniotic stalk;
13- chorion cavity; 14- lacunae; 15- symplastotrophoblast; 16- cytotrophoblast;
17- intraembryonic mesoderm; 18- primitive streak; 19- chorion frondosum;
20- smooth chorion; 21- amnion; 22- body fold; 23- yolk sac; 24-embryo body;
25- amniotic membrane; 26- allantois; 27- chorionic villi
Fig.1 Cleavage in mammals
1 – blastomere;
2 – fertilization membrane
Fig.2 Implantation. Differentiation of trophoblast.
1 – trophoblast; 2 – embryoblast; 3 – epithelium of endometrium;
4 – connective tissue of endometrium; 5 – hypoblast; 6 – epiblast;
7 – roof of amniotic vesicle; 8 – amniotic cavity; 9 – blood vessels of endometrium;
10 – symplastotrophoblast; 11 – cytotrophoblast; 12 – mitosis in cytotrophoblast;
13 – extraembryonic mesoderm; 14 – fibrinoid;
15 – lacunae within symplastotrophoblast; 16 – exocoelomic cavity.
Fig.5 Extraembryonic organs in human
A – the third week;
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