Physiology and biochemistry in modern medicine (1918) (14778274131)

Identifier: physiologybioche00macl (find matches)
Title: Physiology and biochemistry in modern medicine
Year: 1918 (1910s)
Authors: Macleod, John James Rickard, 1876-1935 Pearce, R. G. (Roy Gentry), 1884-
Subjects: Physiology Biochemistry
Publisher: St. Louis : Mosby
Contributing Library: Columbia University Libraries
Digitizing Sponsor: Open Knowledge Commons



Text Appearing Before Image:
. Curve D—The saturation curve in normal blood at 40 mm. carbon dioxide pressure. Since hemoglobin takes up 02 in proportion to its iron, it can not bebecause of changes in the 02 combining part of the hemoglobin itselfthat blood and pure hemoglobin solutions have dissimilar dissociationcurves, but rather because of differences in the environment in which thehemoglobin acts. That this is so can be readily shown by plotting thedissociation curve, not for a hemoglobin solution, but for blood itself RESPIRATION BEYOND THE LUNGS :;s:, (/> in Pig. 138). The results are very different. At a partial pressureof 0., of about 60 mm. Eg that is, a lower pressure than exists in thelung alveoli (100 mm.)—the blood becomes nearly saturated with 02,whereas at pressures below 50 mm. it readily loses 02, so that at 10 mm.there is nearly complete reduction. The question is: What are the environmental conditions under whichthe hemoglobin in the blood so alters its combining power for 02 as to 100
Text Appearing After Image:
60 70 100 20 30 40 50 Fig. 139.—Dissociation curves of hemoglobin. Ordinates—Percentage saturation of hemoglobin.Abscissa—Tension of oxygen in mm. of mercury. I. Dissociation curve of hemoglobin dissolved in water. II. Dissociation curve of hemoglobin dissolved in 7% NaCl. III. Dissociation curve of hemoglobin dissolved in 9% KG.Temperature 37-38° C. (From Joseph Barcroft.) produce such a difference in the dissociation curve? By experimentingwith hemoglobin solutions, three such factors have been found to comeinto play: (1) the presence of inorganic salts, (2) the hydrogen-ion con-centration (C02 tension) of the solution, and (3) the temperature. Ifhemoglobin is dissolved in water containing the varitfus salts of plasmain the same proportion as in blood (artificial plasma), the dissociationcurve will be found to change so as to resemble that of blood (Fig. 139). 386 THE RESPIRATION Since the plasmas of different animals contain different proportions ofsalts, the artificial plas