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.
It divides into two principle bronchi, tubes which conduct air into the lungs, and they divide into two lobar bronchi for the left lung, and into four lobar bronchi for the right lung. These further divide into smaller bronchi and bronchioles within the lung tissue. The structure of the larger bronchi is identical to that of the trachea. On the smaller bronchi the C-shaped cartilage rings are gradually replaced by irregular plaques of cartilage. Bronchioles have no cartilage at all. The bronchioles are less than 1mm in diameter, and undergo further divisions, the last of which is characterised by the loss of goblet cells.