As they contract, the intra-alveolar pressure falls to 759mmHg (due to Boyle’s law).These then contract- enlarging the thoracic cavity (i.e.(accessories include scalene muscles (elevates 1st &2nd ribs) sternocleidomastoid (elevates clavicle) pec major).diaphragm(most powerful- responsible for 75% of thoracic enlargement) also external intercostals (pulls ribs up and forward) Before inspiration, inspiratory muscles are relaxed.Problems with transmural gradients: atelectasis pneumothorax.=Alveolar pressure (760mmHg) – Intrapleural pressure (756mmHg) = 4mmHg Intrapleural fluid cohesiveness– the strength of intrapleural fluids.Two forces hold the thoracic walls and lungs together Because the lungs are elastic and have no muscles, it is important that they are attached to the wall of the chest (which can move to produce ventilation).Intrapleural pressure (~756mmHg) due to the closed pleural space.Intra-alveolar pressure (also ~760mmHg)due to the open communication of the alveoli and the external air.Atmospheric pressure ~760mmHg (decreases with altitude).The respiratory quotient is the rate of CO2 production divided by the rate of O2 consumption. This is a biochemical process that occurs in the mitochondria, using oxygen and carbon compounds (from sugars) and forming carbon dioxide and water. Cellular respiration (Internal respiration)
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