The Respiratory System Structure and Function

The lung is an organ that participates in gas exchange. The tissues and structures unique to the human lung provide for oxygen to be taken up from ambient air and absorbed into the blood while carbon dioxide is released from the blood into the atmosphere. A human being inhales about ten cubic meters (10 m ) of air a day. 

In addition to the oxygen and carbon dioxide exchanged here, this area of the lung is necessarily exposed to other gases (carbon monoxide, nitrogen, etc.) to fluid droplets and to particulates in the ambient air. The air in the lung is essentially saturated with water vapor as it passes through the nasal scrubber to the bronchi, bronchioles, and ducts to the air sacs. 

The complex functions of the lung and pulmonary system are accomplished through a series of specialized cells (more than forty types have been identified), tissues, and structures. Standard medical texts such as Gray s Anatomy (Warwick and Williams, 1973) and Functional Anatomy erf the Lung (Nagaishi, 1972) should be consulted for details, but for our purposes, we describe four features that ensure optimum lung function, before discussing the diseases that affect the system. 

The first is transport. The air, with its variable components, requires the inspiratory activity of the respiratory muscles—namely, the diaphragm and intercostals (the muscle between the ribs). The action of these muscles is under both voluntary and involuntary central nervous system control thus, gas flow can be adjusted to maintain a steady state of gas exchange. Air must also be provided to the upper airway for speech. 

Epiglottis (closes larynx directing flow to esophagus behind) 

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