Immunology | Immune system| Immunity

ORGANS FROM ECTODERM:

The ectoderm gives rise to the outer layer of the skin over the entire surface of the embryo.
The neural tube into which the medullary groove develops loses its original connection with the surface.Anteriorly it becomes enlarged and forms the brain,the remaining portions developing in to the spinal cord.The thickening of the walls of the spinal tube, which forms the cord,diminishes the central cavity,until it becomes reduced to a fine canal Canalis centralis.
The anterior portion of the tube becomes divided by slight constriction into forebrain ,midbrain, and hindbrain.
Hind brain becomes widened from side to side especially infront its flair and the sides thicken which develops into cerebellum,which remains thin and membranous and becomes thrown into series of folds which support a mass of blood vessels, called choroid plexus.
The portion of the hindbrain which does not form cerebellum is converted into medulla.The midbrain grows out dorsally and laterally into a pair of hollow processes called optic lobes.
The forebrain soon becomes separated into 2 parts, the Thalamencephalon behind and the cerebral hemisphere which grow out from the latter in front hollow out growth- the infundibulum ,which extends downwards.
The sides of thalamencephalon give rise to optic vesicles,which grow out until they come in close contact with the surface ectoderm.
The distal end of the vesicles widens cut and forms Retina of eyes stalk giving rise to the optic nerve.
The lining of the mouth cavity is formed from an invagination of ectoderm-the stomoderm and similar ectodermal invagination Proctoderm forms the lining of a small part of the post end of the alimentary canal.
 The lens,cornea,retina of eye,vesicle of inner ear also take thin origin from this layer.

ORGANS FROM ENDODERM:

Endoderm forms the lining of the alimentary canal and lining of all organs,which arise as outgrowths from it.It forms liver which at the beginning appear as an out pocketing of the ventral side near anterior end.It becomes folded and branched to form number of clusters of tubules, all emptying into into a common canal -the bile duct. A lateral  outgrowth of the bile duct forms the gall bladder forms the gall bladder. The pancreas arises in the same way as the liver, but as a pair of outgrowths instead of one,but they form a single organ and their ducts later become connected with the bile duct.

Bladder arises as an outgrowth of ventral side of the alimentary canal. Lungs appear as a pair of pouches from the sides of aesophagus. The Gill slits in the frog appear in the form of five solid outgrowths on each side of the anterior portion of archenteron.