NTS Past Papers Explanation "Gaseous Exchange" 2009 to 2019

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SHORT NOTES: The Air which contains 75% N2, 21% O2 and 4% other gases, enters the body through nostrils, it then enters nasopharynx whose work is to humidify and warm the air to body temperature ( the air has already be cleaned by hairs of nose ) the minute particles which were not captured by nose hairs are captured by schnidarian membrane and then air enters oro pharynx and then to laryngeopharynx the part that connects teh digestive and respiratory sytem, the opining of glottis is coved by a flap of elastic cartilage called epiglottis which prevents food from entering the lungs, air then moves to larynx and then to trachaea which is composed c shaped incomplete rings of hyaline cartilage, trachea divides at 5th throacic vertebrae and give rise to primary bronchus, they divide to form seconadry the tertiary then terminal bronchioles and finally air sacs, each air sac is a bunch of alveoli enriched with blood vessels, the alveoli have simple squamous epithilium and next to it is the basment membrane made up of extra cellular fluid the next membrane is endothelium, together they make respiratory membrane from where diffusion occurs. MECHANISM OF BREATHING: During inspiration volume of thoracic cavity increases as it moves upwards and forwards, the diaphragm contracs and external intercostal muscles contracts too, resulting in decrease in pressure as v@1/P due to this air moves from its higher pressure ie environment to lower pressure ie our lungs. During expiration the volume is reduces by relaxation of diaphragm, and contraction of internal intercostal muscles due to which pressure is increased in lungs as p@1/v so air moves outwards. 1 heamoglobin can bind to 4 oxygen molecules, there is 20ml of oxygen per 100ml of oxygenated blood and 14gm of haemoglobin per 100 ml of blood. Artrial blood has 50 ml of CO2. the normal inspiration and expiration constitutes tidal volume which is 500ml.

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