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The lungs and lung disease
Lung function
Structure
ð Larynx – contains the vocal cord
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ð Bronchus –cartilaginous rings to prevent collapse during inspiration
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ð Terminal bronchiole – no rings on cartilage so collapses when the external
pressure is high
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Alveolar epithelium
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Surface for gas exchange
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Alveolar wall, squamous epithelium cells – very thin provides a short diffusion pathway
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Beating of heart, maintains a steep diffusion gradient for gaseous exchange
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Gaseous exchange:
ð Oxygen diffuses at the alveoli down a concentration gradient through the alveolar epithelium and
the capillary endothelium into the haemoglobin in the red blood cells
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ð Ventilation rate – number of breaths per minute
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ð Expiration reserve volume (ERV) – volume breathed out by a maximum expiration at the end of a
normal expiration
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Inspiratory capacity = TV + IRV
ð Inspiratory capacity (IC) – volume breathed in by a maximum inspiration at the end of a normal
expiration
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Total lung capacity = VC × RC
ð Total lung capacity (TLC) – total volume of lungs
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The external intercostal muscles contract, pulling the ribs upwards and outwards
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The diaphragm contracts – flattening
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The liver piston moves downwards
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Causes an increase in volume of the thorax
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Pressure in the thorax is lower than the atmospheric pressure
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Air is drawn into the lungs along a pressure gradient, increasing the volume of the lungs
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The external intercostal muscles relax, the ribs move downwards and inwards
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The diaphragm relaxes – returns to dome shape
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The liver piston moves upwards
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Causes a decrease in volume of the thorax
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Pressure in the thorax is higher than the atmospheric pressure
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Air is forced out of the lungs along a pressure gradient, decreasing the volume of the lungs
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Caused by mycobacterium tuberculosis
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g
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If bacteria enter the blood stream it can affect other areas of the body
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ð Symptoms: constant coughing that produces sputum, loss of appetite, night sweats, weight loss…
ð TB treated with a combination of drugs (prevents antibiotic resistance) over a 6-12 month period
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ð Narrow airways produce a wheezing sound when exhaling
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Pulmonary fibrosis
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When tissue gets damaged, connective tissue replaces – scar tissue
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Lungs are less able to expand fully
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Harder to force air out
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Symptoms: chest pains, shortness of breath, fatigue…

Emphysema
Fibrosis of alveoli
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Neutrophils produces enzymes (proteases and elastases) which breakdown elastin
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ð Symptoms: shortness of breath, wheezing and fatigue

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