The respiratory system is the biological system of any organism that engages in gas exchange. Even trees have respiratory systems, taking in carbon dioxide and emitting oxygen during the day, consuming carbon dioxide and producing oxygen constantly.
In humans and other mammals, the respiratory system consists of the airways, the lungs, and the respiratory muscles that mediate the movement of air into and out of the body. Within the alveolar system of the lungs, molecules of oxygen and carbon dioxide are passively exchanged between the gaseous environment and the blood. Thus, the respiratory system facilitates oxygenation of the blood with a concomitant removal of carbon dioxide and other gaseous metabolic wastes from the circulation. (Davies, Moores, Pp. 34-45)
The physical properties of respiratory tract secretion (RTS) play a prominent role in the non-specific defense mechanisms of the lung. Viscosity and elasticity, that is flow and deformation, are only two of the physical properties of RTS. Spinability, pourability, adhesiveness and tackiness are starting to be recognized as physical properties of RTS and its is likely that they may be relevant in the pathogenesis of airways obstruction. RTS is a gel, which consists of a cross-linked polymer network dispersed in a liquid solvent. The polymeric structure of the epithelial glycoprotein can be explained in terms of covalent (disulphide) linkages and/or physical entanglement between glycoproteins subunits. Other constituents of RTS such as proteins, lipids, ions and water can influence the physical properties of RTS. (Vidriero, pp. 130-135)
The major function of the respiratory system is gas exchange. Respiration consists of a mechanical cycle of inspiration and expiration, with gaseous exchange occurring in between. Primarily the diaphragm drives inspiration. When the diaphragm contracts, the ribcage expands and the contents of the abdomen are moved downward. This results in a larger thoracic volume, which in turn causes a decrease in intrathoracic pressure.............
