BISC 101 Lecture Notes - Lecture 17: Partial Pressure, Surface Tension, Bronchiole

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BISC 101 – Lecture 17 – Circulation and Gas Exchange: Part II
Gas Exchange
Gas exchange supplies O2 for cellular respiration and disposes of CO2
Gases diffuse down pressure gradients in the lungs and other organs as a result of differences in partial pressure
oPartial pressure is a measure of the concentration of individual components in a mixture of gases
oThe rate of diffusion of a gas is proportional to its partial pressure within the total gas mixture
oA gas diffuses from a region of higher partial pressure to a region of lower partial pressure
oIn the lungs and tissues, O2 and CO2 diffuse from where their partial pressures are higher to where they are lower
Respiratory surfaces
Animals require large, moist respiratory surfaces for exchange of gases between their cells and the respiratory medium
(either air or water)
Gas exchange across respiratory surfaces takes place by diffusion
Respiratory surfaces vary by animal and can include the outer surface, skin, gills, tracheae, and lungs
Ventilation
Ventilation moves the respiratory medium over the respiratory surface
Aquatic animals move through water or move water over their gills for ventilation
Fish gills use a countercurrent exchange system, where blood flows in the opposite direction to water passing over the
gills
Blood is less saturated with O2 than the water it meets, so O2 moves from water into the blood located within the gills
Lungs
The circulatory system (open or closed) transports gases between the lungs and the rest of the body
Lungs are in folding of the body surface
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