Oxygen molecules Study notes

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Simon Fraser University
Biomedical Physio & Kines
BPK 205
Parveen Bawa

Oxygen molecule traveling through the human body: • I’m at the mouth where there are others just like me. 21% of the air is filled with other oxygen molecules. The PO2 is around 150 mm Hg • Diaphragm muscle pulls downwards (start of inspiration) increasing superior- inferior volume of the lungs, and external intercostal muscles pull the outwards increasing anterior-posterior volume • This causes intrapleural pressure in the pleural cavity to drop from -5 cm H2O to get more negative, creating a vacuum that pulls on the alveoli increasing alveolar volume. Increase in alveolar volume will reduce alveolar pressure (boyle’s law); creating a pressure gradient where lowest pressure is in the alveoli, and highest total air pressure is outside the mouth • The reduced air pressure creates a vacuum that sucks me into the mouth. I first travel through the conducting zone where there is no diffusion, only conduction of air. I see that at the trachea there is much connective tissue such as collagen, but not as much smooth muscle. There is much turbulence in the first six bifurcations due to the high velocity that I and other gas molecules are traveling at. As I continue through the bifurcations, I notice that the bronchioles decrease in connective tissue and increase in smooth muscle. There has been humidification on the journey so far. Now there is a greater concentration of myself and other O2 molecules. • Midway through inspiration phase, I enter an alveolus at bifurcation 20. The PO2 has decreased from 150 mm Hg to around 100 mm Hg here in the alveolus. There is CO2 molecules being diffused into the alveolus where the PCO2 is 40 mm Hg. These CO2 molecules come from the capillaries surrounding the alveolus where the PCO2 is 45 mm Hg • As blood flows through the capillaries I finally get diffused into the capillaries across the alveolar wall. This wall is only one layer thick making my transition easy. Wh
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