PRINCIPLES OF TOXICOLOGY - Biology East Borneo

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