ABSORPTION OF IRON FROM GASTROINTESTINAL TRACT 621 



contraction of the spleen, but this may not be the only cause of the increase 

 (cf. 5^3). According to Davis {5I^2), acetylcholine produces a hyperchromic 

 anemia, and the effects on the oxygen supply of the bone marrow hitherto 

 ascribed to choline {cf. Section 5.2.) are actually due to acetylcholine. 



4. ABSORPTION OF IRON AND ITS INCORPORATION 

 IN THE HEMOGLOBIN MOLECULE 



4.1. Iron Requirements 



The normal daily food contains 10-30 mg. iron, but this is partially 

 in a combined form which is not, or is very poorly, absorbed. Widdow- 

 son and McCance {3069) found the average daily intake of iron by 

 men 16.8 mg., by women 11.4 mg. The latter was too small and 

 caused a slight microcytic anemia cured by iron. 15-16 mg. is con- 

 sidered an adequate iron supply for adults (Medical Research Council 

 Report, ISdlf.), 5-6 mg. as the minimum. The iron loss in menstrua- 

 tion is about 50 mg. (higher in menorrhagia), in pregnancy about 

 900 mg., in lactation 1 to 1.5 mg. per day (Witts, Sll^)- The amounts 

 actually required for hemoglobin synthesis are far smaller and 

 decrease considerably after puberty, more so in men than in women 

 {cf. 1197,3103). Absorption and utilization of 25 mg. iron causes 1% 

 increase in the hemoglobin concentration of the blood. 



Iron given intravenously is quantitatively transformed to hemo- 

 globin by anemic dogs (Whipple and Robscheit-Robbins, 3060). 

 The iron set free by hemoglobin breakdown is also retained for the 

 synthesis of fresh hemoglobin with the exception of a small part 

 (2-8%) which is excreted {cf. Chapter XI, Section 10.2.). Iron given 

 by mouth, however, is only partly absorbed, and even the absorbed 

 iron is incompletely used for hemoglobin synthesis, the remainder 

 being stored in liver and spleen. 



4.2. Absorption of Iron from the Gastrointestinal Tract 



By experiments with radioactive iron (Fe^^) Whipple, Hahn, and 

 co-workers have shown that the degree of absorption of iron from 

 the gastrointestinal tract by dogs depends upon the amount of iron 

 stored in the organs {120,1092). Nonanemic dogs absorb very little, 

 anemic ones much more. Most of the iron is absorbed from the small 

 intestine, some also from the stomach and duodenum {2290). The 

 iron absorption depends on the presence or absence of iron stores 

 rather than on the degree of anemia; while it takes several days to 

 produce iron desaturation, physiologic iron saturation is produced in 



