Most WHO departments have their own procedures for supporting research in priority areas-these vary from requesting letters of intent to issuing a call for proposals to commissioning research.
In humans and other mammals, the anatomical features of the respiratory system include trachea, bronchi, bronchioles, lungs, and diaphragm. Molecules of oxygen and carbon dioxide are passively exchanged, by diffusion, between the gaseous external environment and the blood.
1 Irregular rings of cartilage surround the bronchi, whose walls also consist of smooth muscle. 2  Once inside the lung the bronchi split several ways, forming tertiary bronchi. 3  Bronchioles: Tertiary bronchi continue to divide and become bronchioles, very narrow tubes, less than 1 millimeter in diameter.