The endoderm will form the epithelial lining of the digestive system and its glands, the lining of the respiratory tract down to the alveoli, the epithelium of the bladder and urethra.

• 内胚层的分化：分化为消化管、消化腺、呼吸管道、肺以及中耳、甲状腺、甲状旁腺、胸腺、膀胱等器官的上皮。