HUMAN ANATOMY AND PHYSIOLOGY
AN INTRODUCTION TO RESPIRATION
In this essay we will consider a few major aspects of respiration. We shall first consider the interesting history of the study of respiration before moving on to our modern understanding of respiration. We will look at the structure and function of the respiratory system including the upper and lower respiratory tracts with a note on the control system. Secondly we will consider the physiology of respiration. Thirdly we will discuss some of the major common disorders and diseases which affect the system with a special focus on asthma. A BRIEF HISTORY OF THE STUDY OF RESPIRATION Hippocrates "counted air as an instrument of the body" just as food was eaten. Galen (129-200) felt that respiration served a triple purpose: 1) breathing cooled the heart, 2) air needed for production of vital spirits 3) respiration got rid of the friligimous or products of the innate fire burning in the heart. Basically Galen's ideas were followed for many centuries until the era of the 17th century. Robert Boyle (1627-1691) who was primarily a physicist was interested in the weight and pressure of the air and in 1660 he showed that air was essential to both life and combustion by placing a candle and a small animal in a vessel. Robert Hooke (16351703) showed that after the thorax of a dog had been opened life could be prolonged by artificial respiration - this proved that the whole of the essential business of respiration takes place in the lungs. Richard Lower (1631-1691) upset the old ideas that the change in blood colour took place in the heart rather than in the lungs. He also demonstrated the necessity of fresh air in life rather than air generally and that in fact 'where a fire burns readily there we can easily breathe'. He was close to conceptualizing oxygen here but this had to wait until Priestley’s work or perhaps the research of Lavoisier (1743-1794). However, John Mayow (1641-1679) an English chemist had come very close to this conclusion in his experiments. He said that air entered the lungs during inspiration simply because the pressure or elastic force of the atmosphere drove it in to fill in the increased space afforded by the enlarged and dilated thorax. Mayow had also in reality come near to discovering oxygen but did not isolate it or realise that carbon dioxide passed in the reverse direction. However, he had achieved a good deal. The next developments came with Joseph Priestly (1733-1804) but perhaps Lavoisier had the clearest expressions of oxygen and respiration. Finally it was Gaston Magnus, by use of the mercuric air pump that showed that both arterial and venous blood contain both CO2 and O2, though in different proportions. Thus it took many centuries for the links between air, oxygen, carbon dioxide, respiration and blood to be unraveled. Let us now look at modern views of respiration. THE STRUCTURE AND FUNCTION OF THE RESPIRATORY SYSTEM The respiratory system is concerned with the exchange of oxygen and carbon dioxide between the blood and the lungs. This is essential for the provision of energy for cellular metabolic function. Most energy extractions can only take place in the presence of oxygen and the route of oxygen intake into the body is via the respiratory system. Basically inspiration brings in oxygen and expiration excretes carbon dioxide. This is known as the exchange of gases. Before we consider this in more detail let’s look at the main organs of the respiratory system. Firstly we should consider the nasal cavity. As air is breathed in it is warmed and moistened while dust and debris are filtered out by cilia or hairs and mucus producing goblet cells. Air which passes through the nasal cavity joins air which is brought in through the mouth. The nasal cavity itself is divided by the septum. There are openings to the nostrils at the front and to the pharynx at the back. In addition there are small openings to the maxillary, frontal and ethmoidal...
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