. The comparative physiology of respiratory mechanisms. Respiration. 96 RESPIRATORY MECHANISMS would be likely to occur in the living organism. It is a sig- nificant fact that the effect is very pronounced at low oxygen tensions and practically disappears at full saturation. A brief characterization of the affinity of a certain kind of blood for oxygen which is, however, sufficient for many biological purposes (Krogh and Leitch, 1919), can be given by the ten- sions of "loading" (tt) and "unloading" (tu). The loading tension is defined as the tension which will allow the bl
. The comparative physiology of respiratory mechanisms. Respiration. 96 RESPIRATORY MECHANISMS would be likely to occur in the living organism. It is a sig- nificant fact that the effect is very pronounced at low oxygen tensions and practically disappears at full saturation. A brief characterization of the affinity of a certain kind of blood for oxygen which is, however, sufficient for many biological purposes (Krogh and Leitch, 1919), can be given by the ten- sions of "loading" (tt) and "unloading" (tu). The loading tension is defined as the tension which will allow the blood to. Fig. 54. Oxygen dissociation curves of dog's blood at different C02 tensions. (Krogh.) become 95% saturated with oxygen, a figure which comes very close to the normal saturation of arterial blood, while the "unloading" tension corresponds to half saturation. This does not mean of course that the blood becomes necessarily half saturated in the passage through the tissues, but is only a convenient way of expressing the relative facility with which oxygen is given off from the haemoglobin. A high tu increases availability of the oxygen. In Fig. 53 the tu of human haemo- globin at 15°C is about mm, while at 38° it is 8 mm. In the actual human blood the tu is about 30 mm. Generally the loading and unloading tensions are not independent variables, but a high tt is associated with a relatively high tu and vice versa. This means a conflict of interest in the economy of the organism where it is desirable that the // is as low as possible to insure saturation in the. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Krogh, August, 1874-1949. Philadelphia, University of Pennsylvania press
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