Lesson 4: Tuberculosis
The vulnerable respiratory apparatus is easily invaded by microorganisms. Breathing is continuous and as respiratory gases are wafted in and out, infecting organisms find free passage deep inside the body. The site of entry is commonly the nasopharynx, but entry can also occur through the oropharynx and the conjunctiva. The lachrymal glands drain into the nasopharynx and experimental studies have shown that this is often a more certain method of infection than directly through the nose. The respiratory system also includes connections to the middle ear, the sinuses and the gastro-intestinal tract.
The ciliated lining and mucus-secreting cells of the respiratory tract can act as nonspecific host defence mechanisms entrapping microorganisms and passing them to the exterior. In attempting to expel these secretions from the body by coughing or spitting, organisms may be transmitted to
another host. The lymphoid tissues, especially the tonsils and adenoids, guard the respiratory apparatus, but sometimes may themselves become foci of infection.
Tuberculosis (TB) is an infection of the lungs and/or other organs, usually by Mycobacterium
tuberculosis, but occasionally by other species such as Mycobacterium bovis or Mycobacterium africanum. TB may have a long incubation period, produces chronic infection with risk
of reactivation and, without treatment, would often be fatal.