| This may be said to start from the nose, and is | | | | cells (alveoli) which are surrounded by capillaries, |
| composed of the larynx, the wind pipe (trachea), its | | | | through which the blood flows from the heart to the |
| two branches (called "bronchi"), and the lungs. It is | | | | lungs, and back again to the heart. The walls of the air |
| concerned with the vital function of making available | | | | sacks are very thin. They allow gases to pass through |
| the much needed oxygen to the body. It would be well | | | | in both directions. The oxygen from the air sacks is |
| to understand here why we need oxygen so badly for | | | | absorbed in the blood in the capi11aries, and the carbon |
| remaining alive. Our life activity is ever based on | | | | dioxide and water vapour from the capillaries enters |
| biochemical processes which cannot go on without a | | | | the air sacks. This gaseous exchange is a very |
| continuous supply of energy. This energy is received | | | | important phenomenon concerning the respiratory |
| from the food we eat, especially the carbohydrates, | | | | system. |
| fats, and proteins. The end roducts of these | | | | The lungs are made of elastic tissues which expand |
| constituents are supplied to each tissue by the blood. | | | | and contract during respiration. They are contained in |
| The energy stored in these products can be released | | | | what is called the "thoracic cavity" which is |
| for the purpose of life activity of any tissue, only | | | | protected on all sides by the ribs. The base of |
| through the process of oxidation. This is a process in | | | | this cavity is made by a dome shaped band of a |
| which oxygen combines with the substance containing | | | | muscle cal1ed the "diaphragm", which plays an |
| energy, and releases energy along with water vapour | | | | important role in the mechanism of respiration. The |
| and carbon dioxide. This process has to go on | | | | cavity below the diaphragm is called the "abdominal |
| continually in every living tissue of the body, and it is, | | | | cavity". The cavity accommodates organs like the |
| therefore that we can not live without oxygen for | | | | stomach, duodenum, liver, pancreas, kidneys, and |
| more than a few minutes. The carbon dioxide | | | | intestines. |
| produced in the process of oxidation is a poisonous | | | | The act of respiration is composed of three parts, |
| gas, and must be removed from the body as quickly | | | | namely, inhalation, exhalation and pause. During |
| as possible. It is collected, as we have noted earlier, in | | | | inhalation the thoracic cavity increases in volume due |
| the blood flowing in the capillaries. We shall now see | | | | to an elevation and extension of the ribs, along with a |
| how it is eliminated from the body through the | | | | descent of the diaphragm downward. The lungs |
| respiratory system. | | | | expand due to this, and air rushes in through the nose |
| Air from the atmosphere enters our body through the | | | | to fill the vacuum created thereby. The lungs then |
| nose, and goes to the larynx or the sound box, and | | | | contract automatically after a while, due to their elastic |
| then to the wind pipe. The wind pipe further divides into | | | | recoil, expelling some amount of air during exhalation. |
| two branches, one of which goes to the left lung, and | | | | This is foHowed by a state of pause, and then |
| the other to the right lung. They give rise to further | | | | another round of inhalation and exhalation takes place. |
| branches and sub-branches in the lungs. At the ends | | | | Car-bon dioxide and water vapour are got rid of |
| of the minute sub-branches are borne the air sacks or | | | | through exhalation. |