In physiology, respiration (many people mistake this with breathing) is defined as the transport of oxygen from the outside air to the cells within tissues, and the transport of carbon dioxide in the opposite direction. This is in contrast to the biochemical definition of respiration, which refers to cellular respiration: the metabolic process by which an organism obtains energy by reacting oxygen with glucose to give water, carbon dioxide and ATP (energy). Although physiologic respiration is necessary to sustain cellular respiration and thus life in animals, the processes are distinct: cellular respiration takes place in individual cells of the animal, while physiologic respiration concerns the bulk flow and transport of metabolites between the organism and the external environment.
In unicellular organisms, simple diffusion is sufficient for gas exchange: every cell is constantly bathed in the external environment, with only a short distance for gases to flow across. In contrast, complex multicellular animals such as humans have a much greater distance between the environment and their innermost cells, thus, a respiratory system is needed for effective gas exchange. The respiratory system works in concert with a circulatory system to carry gases to and from the tissues.
In air-breathing vertebrates such as humans, respiration of oxygen includes four stages:
Note that ventilation and gas transport require energy to power a mechanical pump (the heart) and the muscles of respiration, mainly the diaphragm. In heavy breathing, energy is also required to power additional respiratory muscles such as the intercostal muscles. The energy requirement for ventilation and gas transport is in contrast to the passive diffusion taking place in the gas exchange steps.
Respiratory behavior is correlated to the cardiovascular behavior to control the gaseous exchange between cells and blood. Both behaviors are intensified by exercise of the body. However, respiratory is highly voluntary compared to cardiovascular activity which is totally involuntary.
Respiratory physiology is the branch of human physiology concerned with respiration.
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There are several ways to classify the physiology of respiration:
Respiration is the process by which oxygen is delivered from the external environment to the cells for cellular exchange. In its proper terminology, it includes the entire process. In terms of visibility, respiration is simply another term for breathing. Respiration includes the inhalation-exhalation process. As unwanted air is expelled from the body during exhalation, the chest 'falls' and a vacuum is created inside the lungs. As new air is then sucked into the body to fill in the vacuum, the chest 'rises'. We call this inhalation. In this process, the unwanted gas expelled is mainly carbon dioxide. This is then replaced during the inhalation breathing phase by the oxygen content within the air inhaled. During this process, via the sacs of the lungs, an exchange of gases first occurs as the blood exchanges carbon dioxide from the body with fresh oxygen. Oxygen attaches to the red blood cells in the blood, and later is diffused from the bloodstream into the intercellular spaces, and eventually diffuses into the cells for use by the cells Therefore, "Respiration" refers to gas exchanged throughout the body with the point of transport of oxygen to the cells for use.
"Cellular Respiration" refers to a specific type of metabolic process that allows an organism to gain energy by breaking down substances.
[1]'Disorders and Diseases of the Respiratory System' Nasal Catarrh is a very common complaint in this country, particularly in cold, damp weather. It manifests itself by excessive mucus secreting through the nose and sneezing. It is often the prelude to or accompanies other diseases. The Common Cold is the result usually of a virus infection and should be. distinguished from a chill, though the latter may provide suitable conditions for the virus to thrive and a cold easily follows a chill. Its extreme ineffectiveness is due to the viruses being transmitted through the air by sneezing. This is known as droplet infection. Catarrh accompanies the cold and this may pass to the throat and along the Eustachian tubes to the middle ear causing earache. If the infection continues further along the bronchial tubes into the lungs, bronchitis may set in. Bronchitis is one of the commonest of diseases in this country and is due to inflammation of the mucous membrane of the bronchial tubes. Laryngitis and pharyngitis are inflammations of the mucous membranes of the larynx and pharynx respectively. They may be preceded by catarrh and both the breathing and the voice are affected in laryngitis while pharyngitis is what we normally call sore throat. Tonsillitis is inflammation of the tonsils and the pharynx can also be affected. The tonsils become enlarged and pain is experienced when swallowing. The cause is usually bacterial infection. Whooping Cough is a common disease of children caused by bacterial infection. The "whoop" which gives it its name is during inspiration. Diphtheria is a very infectious disease, caused by a bacterium, Corynebacteriwn diphtheriae, which starts with an inflammation of the throat. Other symptoms follow and if anti-diphtheritic serum is not administered, post-diphtheritic paralysis may follow. This is not permanent but it takes time for recovery. The well-known Schick test is used to ascertain whether people are subject to the disease and immunization against it is now practiced. Croup occurs when the entrance to the larynx is swollen and constricted and breathing is therefore affected. Asthma attacks may be brought on by a number of agents such as pollen from grasses or by house dust, feathers, the fur of cats or dogs' hair to which these sufferers are allergic. Breathing is extremely difficult owing to constriction of the bronchial tubes. Hay Fever occurs in people whose mucous membranes are extremely sensitive to the pollen of grasses and therefore occurs only during the Summer. Considerable nasal discharge and the usual symptoms of the common cold develop. Antihistamines are often effective in relieving the symptoms. People subject to hay fever should obviously avoid being in a grass field. Pneumonia, of which there are several forms, is an inflammation of the lung tissues and the commonest form is caused by a bacterium, pneumococcus. High temperature, rapid, shallow breathing accompanied by cough and pain in the chest are symptoms. The coughing results in the expectoration of a thick, brown fluid. Sulphonamide drugs and antibiotic treatment are now used with effect. Pneumonia is now often produced by virus infection. Pleurisy is inflammation of the pleurae and may result from pneumonia and other more serious diseases such as tuberculosis. Empyema is a disease in which pus collects in the pleural cavity. This, too, may follow pneumonia and it may be necessary to resort to surgical means to drain off the pus. Silicosis is a hazard of workers in industries in which considerable amounts of silica dust are inhaled into the lungs. Pulmonary tuberculosis or phthisis, commonly called consumption, is caused by Bacillus tuberculosis (Mycobacterium tuberculosis). Once regarded as incurable it inevitably led to death but modern methods of therapy have completely changed the picture. The disease is extremely infectious and may easily be caught from the sputum of an infected person in which enormous numbers of the bacteria live and which get into the air by coughing or into the dust of the air from dried sputum. It may also be acquired from infected milk but the bovine bacillus affects children more than adults. Milk must therefore be adequately protected by pasteurization. Receptacles used by infected persons must on no account be used by healthy people. The name of the disease is derived from the fact that tubercles develop in the lungs, thus tending to obliterate the alveoli. Later these coalesce and the mass breaks down and the particles are discharged in the sputum. As a result cavities develop in the lungs. The disease is now curable and the mortality rate from it has fallen enormously in the last few years. In 1957, 4,784 people died of pul¬monary tuberculosis, but by 1960 the number had dropped to 2,354, a decrease of about 50 per cent. Lung cancer, unlike pulmonary tuberculosis and like other forms of cancer, has been showing a marked increase in mortality rate in recent years. A cancer or carcinoma is a malignant neoplasm, a non-malignant neoplasm being a tumour. Although a cancer may be removed surgically, there is always the danger that the cells may be carried by the blood to other parts of the body where they initiate further cancerous growths. Cancer accounted for 122,648 deaths in 1966 in this country, an increase of 15,500 in ten years, and of these 30,483 were due to lung cancer, an increase of 9,000 over the same period. It has been proved that a minute quantity of carcinogenic (cancer producing) agents are present in cigarette smoke. The inci¬dence of lung cancer has been shown to increase in proportion to the number of cigarettes smoked and as most cigarette smokers inhale, these dangerous substances get into the lungs. The death rate amongst cigarette smokers from lung cancer in this country is three or four times that among pipe smokers and about ten times that among cigar smokers*. Pipe and cigar smoking is therefore very much safer but in non-smokers the death rate from this disease is only about a thirteenth of those among cigarette smokers. These facts speak for themselves. Couple them with the knowledge that of the 615,719 deaths from natural causes in Great Britain in 1966 over 30,000 were due to lung cancer and you cannot fail to see that the matter calls for serious consideration. The morals to be drawn from these facts: do not inhale tobacco smoke into the lungs, smoke a pipe or cigars in preference to cigarettes or, better still, do not smoke at all. Cancer is a disease which has been known to man for a very long time but the number of deaths caused by it have increased out of all proportion to the increase in the population. In this disease cells multiply in a most disorderly and uncontrolled fashion forming malignant growths to the detriment of the normal tissue in which they are growing. Furthermore they can give rise to further cancerous growths in other parts of the body. The cause remains unknown at present and though a cancer virus has been discovered in monkeys, there is no evidence as yet that such is the case in man. Apart from surgery, radiotherapy with radium and X-rays have been used in the treatment of cancer but cobalt-ray treatment now largely supersedes them. Radium was first isolated by M. and Mdme. Curie in 1898 and radioactivity was discovered by Antoine Becquerel in 1890. A German physicist, Wilhelm Rontgen, was the discoverer of X-rays and these are not only used in treatment but also, of course, in diagnosis.
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