We say a high concentration gradient exists when the concentration of a substance differs significantly from one area to another. Consider the animation below the percentage figures refer to the oxygen saturation of the blood or water. In the capillaries of the fish gill, blood with low oxygen concentration travels alongside water with a higher oxygen concentrations.
This creates a steep diffusion gradient along the capillary and favors rapid transfer of oxygen into the blood. Efficiency of the gills is further increased by ventilation,which involves the increase in flow of water over the gills by swimming and by opening and closing their gill flaps. However, oxygen can only diffuse into the blood at the gills if the oxygen level is higher in the water than in the blood — that is, oxygen needs to flow from an area of high levels to an area of low levels.
They achieve this by maximizing the amount of time their blood is exposed to water that has a higher oxygen level, even as the blood takes on more oxygen. Countercurrent oxygen exchange shown in the figure above means the blood flows through the gills in the opposite direction as the water flowing over the gills. This flow pattern ensures that as the blood progresses through the gills and gains oxygen from the water, it encounters increasingly fresh water with a higher oxygen concentration that is able to continuously offload oxygen into the blood.
The low-oxygen blood, which is just entering the gill, meets low-oxygen water. Compression cycle 3. Compressors 4. Expansion valves 5. Refrigerants 6. Evaporators 7. Condensers 8. References 1 Dam, L. Google Scholar Download references. View author publications. Rights and permissions Reprints and Permissions. Copy to clipboard. Comments By submitting a comment you agree to abide by our Terms and Community Guidelines. Search Search articles by subject, keyword or author. Show results from All journals This journal.
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