THE RESPIRATORY FUNCTION OF THE BLOOD OF URECHIS CAUPO

¹ From the Hopkins Marine Station, Pacific Grove, California

1. The blood of Urechis caupo contains hemoglobin enclosed in corpuscles. The oxygen capacity of the blood varies from 2.66 to 7.22 volumes per cent and the percentage of cells in the blood from 18 to 40.

2. The oxygen dissociation curve is measured. Its position does not appear to be influenced by the carbon dioxide pressure. The effect of temperature upon the oxygen dissociation curve is of the direction and order observed in other bloods containing hemoglobins.

3. The carbon dioxide dissociation curve is measured. The ability of the blood to combine with carbon dioxide does not appear to be influenced by the degree of oxygenation of the blood.

4. The buffer value of the blood is 11 volumes per cent and is constant over a considerable range of carbon dioxide pressures. The concentration of hemoglobin accounts for the entire buffer effect.

5. Carbon dioxide is about equally distributed (in concentration) between the corpuscles and plasma. The plasma contains at most a negligible quantity of buffer material. With increased carbon dioxide tension there is a small, but distinctly limited exchange of material between the corpuscles and plasma which increase the ability of the latter to combine with carbonic acid.

6. The hemoglobin in vivo is almost completely saturated, but the pressure of oxygen in the blood may be considerably less than that in the surrounding water. The carbon dioxide content in vivo is 7 and 9 volumes per cent, corresponding to a carbon dioxide pressure of about seven millimeters Hg. The reaction of the blood is estimated to be about pH 7.1.

7. The "ventilation" of the respiratory organ, the hind-gut, is considered quantitatively, the result indicating that the respiratory activity is nicely adjusted to the metabolic requirements.

8. The function of hemoglobin and its relation to the oxygen supply during low tide are discussed. It is suggested that the movement of water within the flats due to changing tidal level is important in supplying oxygen when the tide is out.

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				R. E. Weber and S. N. Vinogradov Nonvertebrate Hemoglobins: Functions and Molecular Adaptations Physiol Rev, April 1, 2001; 81(2): 569 - 628. [Abstract] [Full Text] [PDF]