Pneumonias - a dynamic relationship between the human organism and the etiologic agent.

Pneumonias are usually acute infectious processes of the pulmonary parenchyma, being the result of the overcome of the natural defence mechanisms of the human organism, which lead to the penetration, persistence and multiplication of a biologic agent (which has become a pathogen agent) within the lungs. This is a phenomena which generates local manifestations (inflammation) and systemic manifestations, their variable dimension (which is conditioned by the state of the host and/or the virulence of the pathogen agent) explaining the clinical, paraclinical and biological dimensions of the phenomena. The current material deals on one hand with the phenomena which takes part in the formation of the heterogeneous spectrum of the pneumonias and, on the other hand, we will demonstrate the manner in which the expansion and the severity of the infectious phenomena depend on the virulence of the etiologic agent, on the manner in which the defence mechanisms have been overcome, and also on the biological state of the invaded organism.