1050 



HANDBOOK OF PHYSIOLOGY 



CIRCULATION II 



SIGNIFICANCE OF SOME REGIONAL LYMPHATICS 



Thoracic Duct 



The size, high rate of flow and accessibility for 

 cannulation have made the thoracic duct the duct 

 of choice in studies on lymph. A considerable amount 

 of data has therefore accumulated during the last 

 125 years relative to its characteristics under a variety 

 of conditions in many species, including man (50, 

 51). During the last decade, as previously indicated, 

 the advent of polyethylene tubing made possible 

 chronic experiments in which the cannulas could be 

 left in place and the data collected in the unanes- 

 thetized animal and man and in a reasonably ''nor- 

 mal" physiological situation. 



The thoracic duct receives lymph from the ab- 

 dominal viscera, the lower part of the trunk, and the 

 lower extremities, and empties it into the jugular 

 vein. The rate of flow in the thoracic duct is greater 

 than the sum total of flow from all other ducts. 

 Yoffey & Courtice (234) have assembled available 

 data on the rates of flow in the dog, cat, rabbit, rat, 

 horse, bull, cow, goat, and man. To this list may be 

 added the data of Shrewsbury on the mouse (198). 

 It is interesting that in spite of the many variables 

 involved in the experimentation (anesthesia, time of 

 feeding, duration of collection, etc.) the thoracic 

 duct lymph flow in all species studied averages about 

 2 ml per kg per hour in nonruminants and somewhat 

 more in ruminants. If we accept the average figure 

 for plasma volume for most animals of 45 ml per kg, 

 it is obvious that the amount of lymph returned to the 

 blood stream via the thoracic duct per 24 hours is 

 roughly equivalent to the plasma volume. The above 

 calculations are in terms of the quiet, resting animal. 

 Under conditions of activity, the return is consider- 

 ably greater. 



Hepatic Lymph 



The contribution of the liver to thoracic duct 

 flow appears to be variable. It may contribute from 

 one-fourth to one-half of the flow in the dog (33) 

 and cat (149, 150), and only about 10 per cent in 

 rats (138). Actually, the anatomy of the hepatic 

 lymphatic drainage is such that direct measurement 

 of total hepatic lymph flow is difficult and the data 

 available have been derived from indirect estimates 

 or from experiments where usually only one large 

 hepatic duct was cannulated. The values obtained 

 by such direct cannulation (0.4-1.2 ml kg hour) 

 suggest that liver lymph flow is higher than that of 

 any other part of the body of the clog. 



Two hilar lymphatic pathways have been described 

 for the canine liver (184): /) a main hilar system, 

 draining predominantly the right lobes; and 2) an 

 accessory hilar system, draining mainly the left lobe. 

 Usually all of the hilar lymph seems to pass into one 

 common efferent trunk which then discharges it into 

 the cisterna chyli. About 80 per cent of lymph leaving 

 the canine liver probably travels by the hilar route 

 and the remaining 20 per cent by the hepatic venous 

 lymph route. 



Not only is liver lymph flow higher than from any- 

 where else in the body, but it also has the highest pro- 

 tein concentration, equaling from 80 to 95 per cent of 

 plasma concentration in dogs, rats, and cats ( 141 , 149, 

 1 57, 158, 234). Electrophoretic analyses show that 

 protein distribution in hepatic lymph is similar to that 

 in plasma. These data are derived from acute experi- 

 ments on anesthetized animals, from animals with 

 chronic lymph fistulae, experiments in which T-1824 

 or other dyes have been used to label proteins, and 

 from isolated liver preparations. 



The extraordinarily high permeability of the hepatic 

 endothelia involved in hepatic lymph formation has 

 been demonstrated by the use of dextran fractions of 

 graded molecular weights (92, 141 ). While the results 

 of these investigations differ in details, they are con- 

 sistent in showing that high molecular weight dextrans 

 appear in hepatic lymph in greater concentration than 

 in lymph from other areas (fig. 4) and suggest that 

 hepatic lymph represents a plasma filtrate formed in 

 a region of highly permeable capillary walls. In a 

 recent review of hepatic circulation (27) Brauer sug- 

 gests: "As a working hypothesis compatible with the 

 major part of the available data, one may accept the 

 following: Liver lymph formation involves two sites. 

 The first of these would appear to be the sinusoidal 

 portion of the hepatic vascular tree where a very large 

 area of endothelium with demonstrably large pores 

 surrounds the blood stream, and where one would ex- 

 pect the formation of a large volume of lymph, differ- 

 ing from the blood principally in the absence (in the 

 normal liver, at least) of erythrocytes and of the greater 

 part of the leukocytic elements. This primary lvmph 

 for the most part moves countercurrent to the blood 

 stream to enter the lymphatic vessels within the Glis- 

 son sheath. Here it passes through the peribiliary 

 plexus, the second site important in liver lymph forma- 

 tion. The principal role of this plexus in the normal 

 liver should be sought in the opportunity it provides 

 for secondary modification of liver lymph composi- 

 tion by exchange of soluble components between bile, 

 lymph, and blood."' 



The high rate of flow of hepatic lymph coupled 



