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.
The bronchi are the tubes which carry air from the trachea to the inner recces of thelungs, where it can transfer oxygen to the blood in the alveoli. Two main bronchi, the right and left bronchus, branch off of the low end of the trachea in what is called the tracheal bifurcation.