| Popis: |
This chapter describes the process of carbon dioxide transport and excretion in fishes. Metabolism produces CO 2 at variable rates that are dictated by aerobic metabolic requirements. In most fish species that have been examined, the majority of CO 2 is excreted across the gill into the water as O 2 is absorbed across the gill into the blood. The processes of O 2 uptake and CO 2 excretion share common pathways, are governed by several mutual principles, and are intricately related. In teleost fish, the high CO 2 capacitance of true plasma predominantly reflects the buffering power of red blood cells. CO 2 added to the blood diffuses into RBCs, where extensive formation of HCO 3 - is facilitated by end-product removal. It is found that as blood arrives at the gill, it contains carbon dioxide predominantly in the form of HCO 3 - dissolved in the plasma. Within the transit time through the gill vasculature, sufficient HCO 3 - is converted to molecular CO 2 and excreted at a rate that matches production at the tissues. It is observed that the direct excretion of HCO 3 - through the mechanism, though important for ionic and acid-base regulation, likely accounts for less than 5% of total carbon dioxide excretion. |
