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HANDBOOK OF PHYSIOLOGY 



CIRCULATION II 



15 cm FLO. Pressure levels in veins and lymphatics 

 were generally very similar at rest, the venous pres- 

 sures being only slightly higher. It would thus seem 

 that pressure in the lymphatic capillaries may be 

 comparable to the pressure in the venous end of 

 capillaries at rest. These authors found the leg 

 lymphatic pressure to fluctuate with respiration. With 

 increased venous pressures, lymphatic pressure rose 

 slowly but never reached the level of venous pressure, 

 a reflection, perhaps, of the distensibility of lymphatics 

 (156) and collection of fluid in the tissues. Similar 

 experiments in our laboratory (Miller, unpublished) 

 on the anesthetized dog also showed a lack of direct 

 correspondence between leg lymphatic and venous 

 pressures under a variety of experimental procedures. 



DISTRIBUTION OF LYMPHATIC VESSELS 



Although lymphatic capillaries spread into a tissue 

 after the blood vessels, the density of the lymphatic 

 plexus does not always run parallel with the richness 

 of the blood supply. Furthermore, capillary plexuses 

 vary tremendously in richness in different organs 

 and tissues. For example, they are abundant in the 

 dermis, the conjunctiva, the periostium of bone, and 

 in the mucosa and submucosa of the alimentary, 

 respiratory, and genitourinary tracts, but are pre- 

 sumably absent in cartilage, bone marrow, the central 

 nervous system, epithelium, and fetal part of the 

 placenta (62). Voluntary muscle contains lymphatics 

 only in fascial planes. It is generally believed that 

 lymphatic capillaries do not actually reach the pul- 

 monary alveoli, but that their distribution ceases at 

 the beginning of the respiratory portion of the ulti- 

 mate lung structure, the atrium leading into the 

 alveolus. Likewise in the liver, the ultimate functional 

 unit, the lobule, is not supplied with lymphatic 

 capillaries. The fluid leaving the liver sinusoids passes 

 through capillary endothelium and, in the lobule, lies 

 between this endothelium and the liver cells. Lym- 

 phatic capillaries are found at the periphery of the 

 lobule, and these carry the highly proteinized liver 

 lvmph to collecting trunks which join the thoracic 

 and right lymph ducts. In the spleen, too, lymphatics 

 are observed only in the capsule and the thickest 

 trabeculae. Fluid which filters through the walls of 

 the capillaries and sinuses must permeate the stroma 

 before reaching the lymphatic vessels. 



Lymphatic vessels in the kidney appear to begin 

 blindly in two areas (181). The first of these is near 

 Bowman's capsule, and the second is beneath the 



mucosa of the papilla. Two networks of lymphatics 

 then arise, accompanying venous and arterial blood 

 vessels of the kidney. Those which originate in the 

 medulla drain upward and outward toward the 

 arcuate vessels, where they join with those beginning 

 near Bowman's capsule draining in the opposite 

 direction. When the junction occurs, larger trunks 

 then drain with the arcuate vessels toward the hilum 

 of the kidney. They may be seen around the renal 

 artery. There do not seem to be any demonstrable 

 lymphatic channels in the glomeruli or about the 

 afferent and efferent arterioles. 



The lymphatic drainage of the eye has only re- 

 cently been clarified (165). The explanation of the 

 almost zero concentration of proteins in the anterior 

 chamber has long been a major problem since no 

 lymphatic drainage had previously been described. 

 Papamiltiades, in an anatomical study of lymphatics 

 at the iridocorneal angle of the eye, described lym- 

 phatic pathways in the neighborhood of the canal of 

 Schlemm (possibly connecting with the canal) ade- 

 quate to allow continual removal of proteins from the 

 anterior chamber. 



General Anatomic Arrangement 

 of the Main Trunks 



The large lymphatic trunks join the subclavian or 

 jugular veins near their junctions. On the left side, 

 the deep cervical duct, draining the head and neck, 

 the subclavian duct, draining the arm, and the 

 thoracic duct, draining the abdominal viscera and 

 lower extremities, enter the venous system in close 

 association with one another. The left broncho- 

 mediastinal trunk, draining the left sides of the thorax, 

 lung, and heart may join the thoracic duct in the neck 

 or open independently into the junction of the left 

 subclavian and internal jugular veins. Sometimes all 

 of the trunks empty into a sinus or dilatation from 

 which the lvmph then empties into the vein; at other 

 times, thev may form a network before entering the 

 vein or they may all enter the vein close together 

 but independently of one another. On the right side, 

 the right jugular trunk, draining the head and neck, 

 the right subclavian trunk, draining the right upper 

 extremity, and the right bronchomediastinal trunk, 

 draining the right side of the thorax, lung, and heart 

 and part of the convex surface of the liver, empty into 

 the right lymphatic duct which, in turn, ends in the 

 right subclavian vein at its angle of junction with the 

 right internal jugular vein. As on the left side, the 



