Describe the formation and fate of three germlayers inamammalian embryo.

Explanation

Formation of Germs layers/Embryonic Layers. After the formation of the primitive streak, cells of the epiblast move invward:below the primitive streak and detach from the epiblast. This inverting movement is called invagination. (i) Once the cells have invaginated, some of them displace the hypoblast forming the endoderm. Endoderm develops first during embryonic development. (ii) Other cells remain between the epiblast and newly formed endoderm forms the mesoderm: (iii) Cells remaining in the epiblast form ectoderm.

These three germ layers i.e., ecto, meso and endoderm form all the tissues and organs of the body.
Fate of Germ Layers in mammalian embryo. Each germ layer gives rise to the specific issues, organs and organ-systems.
1. Ectoderm. It gives rise to (i) epidermis of skin, and epidermal derivatives (glands, hair, lails), (ii) nervous system, (iii) medulla of adrenal gland, posterior and intermediate lobes of pituitary gland, pined gland (iv) eye (conjunctiva, cornea, lens, retina, iris and ciliary muscles), (v) internal ear, (vi) nasa epithelium, (vii) lining of stomodaeum and proctodaeum, (viii) lining of external aucutory canal, (ix) lacnmal glands, salivary glands, and (x) enamel of teeth. 2. Mesoderm. It produces (i) dermis of skin, (ii) most muscles, connective tissues, (iii) peritoneum, (iv) kidneys, (v) cortex of adrenal glands, (vi) gonads, (vii) urinary and reproductive ducts, (viii) heart blood and lymph vessels, (ix) spleen (x) wall of gut except its lining epithelium. (xi) pericardium and pleura, (xii) sclera and choroid of eye, (xiii) most of skeleton, (xiv) dentine of teeth, (xv) mesenteries, and (xvi) notochord. 3. Endoderm. It forms (i) lining of gut except that of stomodaeum and proctodaeum, (ii. gastric and intestinal glands, tongue epithelium, liver, pancreas, anterior lobe of pituitary gland. thyroid gland, parathyroid glands, thymus gland, (iii) lining of trachea, bronchi and lungs, (iv) lining of urinary bladder, (v) lining of middle ear, (vi) primordial germ cells, and (vii) greater part of prostate.