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HANDBOOK OF PHYSIOLOGY 



CIRCULATION II 



merits on two beagles to which they gave C0 58 -Bi_. by 

 stomach tube and measured its absorption and dis- 

 tribution between thoracic duct lymph and plasma. 

 They found only a very small amount of the total 

 dose in lymph which they believe to have leaked from 

 the plasma. They interpret their results as suggestive 

 that vitamin B12 is absorbed directly into the blood 

 stream as a compound with a molecular weight only 

 slightly higher than that of pure crystalline B]>. If it 

 were absorbed as the entire intrinsic-factor-molecule 

 (mol wt ± 70,000) more should have been found in 

 the lymph, since this large molecule probably cannot 

 easily get into the plasma. 



Coagulation Principles 



Lymph from all parts of the body clots, but does 

 so less readily than plasma. The concentrations of 

 fibrinogen and of prothrombin in lymph are always 

 less than in plasma and vary considerably in different 

 regions just as concentrations of other proteins vary. 

 Mann et al. ( 1 39) drained intestinal lymph from rats 

 and found that marked hypoprothrombinemia de- 

 veloped rapidly, usually within 24 hours. If adequate 

 amounts of vitamin K were administered parenterally, 

 a normal level of prothrombin was maintained, 

 despite loss of lymph. Transfusion of twice the animal's 

 normal volume of plasma did not maintain a normal 

 value for prothrombin while lymph was lost. Under 

 the conditions of their experiments, it appeared that 

 vitamin K was absorbed practically exclusively 

 through the lymph and very little of it was stored, 

 whereas the turnover of prothrombin was extremely 

 rapid. 



The concentration of fibrinogen of canine thoracic 

 duct lymph is about 50 per cent that of plasma (29, 

 70). Brinkhous & Walker (29) found that the mean 

 prothrombin level, expressed as a percentage of that 

 in the plasma, was 93.2, 51.2, and 7.6 for hepatic, 

 thoracic duct, and leg lymph, respectively. These 

 findings are consistent with the known differences in 

 permeability of capillaries to macromolecules in the 

 leg and liver. Infusion of heparin into anesthetized 

 dogs (214) prolonged thrombin and prothrombin 

 times of plasma immediately, but the effect was 

 delayed in thoracic duct lymph and required larger 

 doses for its production. The differences between 

 plasma and lvmph were more marked with cervical 

 lvmph, which again may reflect the differences in 

 permeability between the capillaries in the areas 

 drained bv the cervical and thoracic ducts. 



Langdell et al. (120) have extended and, in general, 

 confirmed these observations. They also found that 

 lymph samples are not fully active at the time of 

 collection. On exposure to glass surfaces in the pres- 

 ence of anticoagulant, the clotting time becomes 

 shorter during the first 20 to 40 min. Coagulating 

 lymph has a high residual prothrombin even after 

 18 to 24 hours in glass containers. Thoracic duct 

 lymph contains sufficient thromboplastic materials 

 so that adequate amounts of thrombin can form to 

 produce a fibrin clot, but it does not contain the 

 thromboplastic materials required for complete 

 prothrombin utilization. These authors conclude 

 "thoracic duct lymph in this respect might be com- 

 pared with platelet-poor native plasma; however, 

 the initial phase of relatively rapid prothrombin 

 utilization in clotting lymph is unlike the slower 

 initial utilization reported to occur in platelet- 

 deficient plasma systems. The nature of the thrombo- 

 plastic material in lymph is not known, but it would 

 appear that the lipid materials being transported 

 could furnish clot-accelerating activity. Additional 

 studies are needed to evaluate the role of the lipid 

 materials in the coagulation of lymph. Such studies 

 promise to furnish considerable information on the 

 role of alimentarv lipemia on blood coagulation since 

 lymph drains directly into the venous circulation." 



Iron 



The demonstration of iron within leukocytes of 

 the intestinal villi, subsequent to the oral administra- 

 tion of iron, led Macallum, in 1894, to suggest that 

 leukocytes are partially responsible for the transfer 

 of iron from the intestine (133). Since then, other 

 investigators (81, 84) demonstrated an increase of 

 iron within mesenteric lymphatics after oral iron 

 administration and suggested that lymphatics are 

 involved in iron absorption and transport. Histo- 

 chemical studies indicated that phagocytes might be 

 concerned in mediating the transfer of iron from the 

 intestine into the lymphatics (84), but more recent 

 evidence does not support these concepts. Thus, 

 Moore et al. (147) showed that iron absorbed from 

 the intestine of dogs passes directly into the blood 

 stream and only a minimal amount appears within 

 the intestinal lymphatics. Endicott et al. (68) showed 

 that the iron demonstrable in intestinal lymph of 

 dogs and guinea pigs was derived from sources other 

 than a single test meal. They showed that in the dog 

 iron was transported chiefly via the portal vein with 



