PRINCIPLES OF TOXICOLOGY

mucous, and the poor drainage characteristics of the sinuses lead to the growth of bacteria. Some
individuals who suffer some sinusitis have severe headaches while others may experience only a
continuous “postnasal drip.” Many factors can contribute to sinusitis, in addition to or in conjunction
with inhaled toxins, such as allergic hypersensitivity, individual characteristics of the sinuses in each
person, and climatic conditions.
Tracheobronchiolar Region
9.1 LUNG ANATOMY AND PHYSIOLOGY 171
Figure 9.2 Sagittal view of the skull, showing nasal turbinates and sphenoid sinuses. [Reproduced with permission
from Fenn and Rahn (1964) (see Figure 9.1 source note).]
The trachea is a tube surrounded with cartilaginous rings that connects the nasopharyngeal region with
the bronchioles. This region is essentially a conducting airway system to the lungs. The bronchi are a
sequence of bifurcating branches of tubes. Each tube divides into two or three smaller tubes, and each
successive branch then divides into smaller tubes, and so on. (see Figure 9.3). The bronchi themselves
do not allow for the absorption of oxygen or carbon dioxide across their surfaces; they are merely