The wall of trachea is composed of four layers: the mucosa, the sub-mucosa, the cartilaginous layer, and the adventitia. Through classic hand-drawn diagram, this video talks about the composition and function of each layer in detail. Timeline: 00:09 introduction 00:42 layers of trachea 01:17 the mucosa 02:04 the sub-mucosa 03:00 the cartilaginous layer 05:03 the adventitia