13 respiration 118 - Biology 118 12. RESPIRATORY PHYSIOLOGY...

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Biology 118 12. RESPIRATORY PHYSIOLOGY GAS EXCHANGE : The basic reaction cells carry out during aerobic metabolism: Glucose + oxygen water + carbon dioxide + ATP Gases enter and leave cells by diffusion, driven by pressure gradients. But for large animals like us, it’s impossible to expose all of our cells to the surrounding air, so diffusion must be supplemented by bulk flow – breathing. RESPIRATORY EPITHELIUM : A respiratory epithelium is the area across which gas diffusion occurs. These surfaces depend on rapid diffusion, so: They must consist of living cells These cells must be kept moist – gases dissolve in water. Surface area must be maximized, and distances must be minimized. AIR CONDUCTION : The nose/mouth, the pharynx/larynx, the trachea, and the bronchial tree serve to conduct air between the outside world and the lungs. Air is warmed and humidified before it reaches the lungs (and cooled and dehumidified before leaving the body). Another important function is filtration: foreign particles in the air must be trapped and eliminated before they reach the lung tissue. Cells lining the airways are constantly secreting mucus, which traps foreign particles in the air. The mucus is then moved towards the throat, by cilia, where it is swallowed and eliminated. Irritation of this lining, some infections, and low temperatures can cause the cilia to slow/stop their waving action, or may increase mucus production – this leads to coughing, or a runny nose. LUNGS : The lungs are made of spongy, elastic tissue, and are located in the thoracic cavity. Two pleural membranes surround the lungs; one membrane coats the lungs, and another coats the interior of the thoracic cavity. In between the pleural membranes is a fluid-filled pleural cavity – the fluid acts as a lubricant and
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13 respiration 118 - Biology 118 12. RESPIRATORY PHYSIOLOGY...

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