The lungs are composed of various specialized cells and tissues -- not just simple tubes or pipes. Lining them are epithelial cells with specialized hairs, or cilia, which help trap particles and prevent infection from reaching the lungs. They also help push foreign and waste matter out of the lungs when necessary. Beneath these cells is the "basement membrane" that forms a firm foundation for the epithelial cells, and under that is looser tissue full of mucous glands and other specialized cells such as eosinophils, mast cells, lymphocytes, and white blood cells called polys. Under this layer is smooth muscle.
