The human respiratory system’s purpose is to allow the intake, exchange and output of gasses necessary to the body in order that the optimum cellular activity may take place. The actual mechanics of the breathing process happens without conscious effort as part of the autonomic nervous system’s role. The most important respiratory muscle in the breathing process is the diaphragm, (Sears and Winwood 1983), which divides the thorax from the abdomen. The muscles between the ribs, the Intercostals, are also part of the mechanical process. The chest cavity expands and the elastic tissue in the lungs also expands. When the body inhales air from the outside, the diaphragm and the intercostal muscles contract. This means that internal pressure, i.e. within the chest cavity, is now lowered in comparison with that of the outside air. Consequently, air from outside rushes into the lungs because it is travelling from a high to a low pressure environment. The lungs inflate and O2 travels to the alveoli. Exhalation happens as a reverse of this process. The diaphragm and intercostal muscles now relax making the chest cavity smaller, reducing the volume, and raising the internal pressure to being above that of the outside air. And so the higher pressured air from the lungs flows out of the airways to the outside of the body. This constitutes one cycle of breathing. Figure 1. The Pressure and Volume changes that bring about ventilation. http://www.google.co.uk/imgres?imgurl=http://solidglow.com/wp-content/uploads/2011/12/49998-breathing-diagram-illustration.jpg&imgrefurl=http://solidglow.com/category/health/&h=586&w=624&sz=116&tbnid=x Once the air has been taken into the lungs, it travels down to the smallest of the air passages and thence into the air sacs, the Alveoli. They are hollow and made of the thinnest, i.e. one cell’s thickness, squamous cells, creating a moist atmosphere for the air and the smallest possible barrier for the gas exchange to occur over...
References: Indge, B, ( 2007). Complete A-Z Biology Handbook. 3rd Edition. Hodder and Stoughton, UK.
Norris et al. ( 2011 ). Anatomy and Physiology for Dummies. 2nd Edition. Wiley,US.
Sears, W. G. Winwood, R. S. ( 1983). Anatomy and Physiology for Nurses. 5th Edition. Arnold, UK.
Please join StudyMode to read the full document