Lungs

Introduction

The lungs are one of the two components in the respiratory system, the other being the chest wall. The main function of the lungs is to allow oxygen to diffuse into the bloodstream and for carbon dioxide to diffuse out into the environment [1]. In addition to this, the lungs also have a variety of non-respiratory functions. This includes functions such as altering pH, protecting the heart, and thermoregulation [1]. The lungs are also continually exposed to pathogens entering through inhalation [2]. It is therefore important for the lungs to have defense mechanisms to protect against any foreign matter [2].

Description of The Lungs

Anatomical Description

There are two lungs in the body occupying the majority of the thoracic cavity; the base sits on the diaphragm and the apex projects above rib 1 [3]. The lung consists of a highly vascularized series of airways and alveoli [1]. This degree of vascularization aids in efficient gas exchange between blood vessels and alveoli [1].

Physical Environment

The temperature in the lungs is around 37oC, equivalent to normal body temperature [4]. The similarity is due to the fact that your body warms the air to 37oC as it passes through your airways [4]. Breathing in cold air can impair healthy lung functions; can lead to allergic reactions and asthmatic attacks [4].

The pH in healthy lungs is between 7.38 and 7.42, equivalent to the pH of the blood that travels through the body [5]. By altering the concentration of carbon dioxide exhaled the lungs can monitor and maintain pH in the body [1]. Many microbes are sensitive to pH; being unable to survive if the pH is either too low or too high.

At body temperature, 37oC, the relative humidity of the lungs ranges from 30% to 70%, whereas recommended humidity ranges from 30% and 50% [6]. The relative humidity tends to be higher in the summer [6]. High humidity can cause problems since high humidity lends itself to optimal microbial growth [6]. Humidity is lowest during winter months [6]. Low humidity can be problematic as dry air makes mucous membranes dry, making them more susceptible to infection [6].

Microbes in the lung

Opportunistic Pathogens

Although it is widely believed that the lungs are a sterile environment [7], there are some microbes that can be considered to be part of the normal flora [8]. Some examples are Burkholderia cepacia complex, Chlamydophila pneumonia, Pseudomonoas aeruginosa [8], Aspergillus, Penicillium, and Candida [9].