. The biology of marine animals. Marine animals; Physiology, Comparative. 176 THE BIOLOGY OF MARINE ANIMALS capacities are shown by some diving mammals, up to 30% (Table ). Most bloods become saturated with oxygen below atmospheric tension. The affinity for 02 is characterized by the dissocation curve, connecting degree of saturation of the blood (percentage) with tension of 02. Stand- ard values, which indicate the nature of the dissociation curve and its useful range, are given by tensions of loading and unloading. Loading tension (fz) refers to the tension at which the blood becomes 95
. The biology of marine animals. Marine animals; Physiology, Comparative. 176 THE BIOLOGY OF MARINE ANIMALS capacities are shown by some diving mammals, up to 30% (Table ). Most bloods become saturated with oxygen below atmospheric tension. The affinity for 02 is characterized by the dissocation curve, connecting degree of saturation of the blood (percentage) with tension of 02. Stand- ard values, which indicate the nature of the dissociation curve and its useful range, are given by tensions of loading and unloading. Loading tension (fz) refers to the tension at which the blood becomes 95 % saturated with 02; tension of unloading (tu) corresponds to half-saturation. Some oxygen dissociation curves for haemoglobins of different animals are. 10 20 30 40 50 60 10 Oxygen tension (mm Hg) 80 90 Fig. Oxygen Dissociation Curves for Haemoglobin of Several Marine Animals Curves: 1: Arenicola marina, 20CC, pH 7-3; 2: Anguilla bostoniensis, 20CC pH 7-3; 3: Petromyzon marinus, 20CC, pH 74; 4: Opsanus tau, 20°C, C02 1 mm Hg; 5: skate, 10-4°C, C02 1 - 0-5 mm Hg; 6: Phoca vitulina, 38°C, C02 46-47 mm Hg. (From various sources.) shown in Fig. , and values for tensions of saturation (loading) and half-saturation are listed in Table Function of Haemoglobin. Haemoglobins of different animals often possess quite dissimilar dissociation curves. The tension of half-saturation indicates the facility with which 02 is transferred from blood to the tissues: a high value for tu increases the availability of 02 to the tissues; a low value indicates that oxygen is available only when supplies in the tissues are nearly exhausted, and tensions are very low. Saturation tension is linked with unloading tension, but does not become functionally signific- ant until oxygen becomes depleted in the external medium, and falls below 100 mm Hg. The dissociation curve is typically sigmoid in shape, the slope differing greatly from species to species (Fig. ). At one extreme are anim
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