ANATOMY AND PHYSIOLOGY OF THE VASCULAR WALL 



7 Z 3 t S S 7 8 9 10 It IZ 13 IV IS 16 17 IB '9 20 21 22 23 29 ZS 26 27 26 29 30 31 32 

 Obere Exfreraitat \ Thorax \ Bavchttoh/e J \ Unterz Extremitat 



fig. 14. Percentage of transverse (circular) muscles (black columns), longitudinal muscles (white 

 columns), and collagen and elastic tissue (hatched columns) of the human veins at different sites 

 1 : Skin vein of the forearm; 2 : v. mediana cubiti; 3 : v. basilica; 4: v. comitans of the a. brachialis 

 5: v. brachialis, proximal part; 6: v. comitans of the a. circumHexa humeri dorsalis; 7: v. axillaris 

 8: v. brachiocephalica dextra; 9: v. thoracica interna; 10: v. thoracica longitudinalis dextra; 1 1 : v 

 cava cranialis; 1 2 : v. cava caudalis; 13: v. portae; 14: v. coronaria ventriculi; 15: v. lienalis; 16: v 

 renalis sinistra; 1 7 : v. renalis dextra; 18: v. mesenterica caudalis; 19: v. cava caudalis, most distal 

 part; 20: v. spermatica; 21 : v. iliaca communis sinistra; 22: v. iliaca communis dextra; 23 : v. dorsalis 

 penis subcutanea; 24: v. saphena magna of the thigh; 25: v. femoralis; 26: v. poplitea; 27: v. saphena 

 of the shank; 28: v. comitans of the a. tibialis posterior; 29: v. comitans of the a. tibialis anterior; 

 30: v. comitans of the a. dorsalis pedis; 31 : skin vein of the back of the foot; 32 : v. comitans of the 

 a. plantaris fibularis. [v. Kiigelgen (48).] 



organ, the anastomoses may open and let the blood 

 bypass the capillaries. 



Anastomoses in the lung possess longitudinal 

 muscles. Weibel (96, 97) has demonstrated that these 

 muscles always appear in those vessels which have 

 to withstand longitudinal elongation. He assumes 

 that the longitudinal muscles support this stretch. 



Veins 



The veins, in contrast to the arteries, are verv 

 variable in their wall structure. Usually they have a 

 larger percentage of collagen fibers than the arteries, 

 but there are veins in which the muscular mass exceeds 

 by far that of the collagen fibers. Veins have little 

 elastic tissue (fig. 1). The arrangement of the wall 

 elements is both circular and longitudinal in varying 

 proportions in different veins. Tension muscles seen 

 attached to elastic fibers in arteries seldom appear 

 in veins. Grau (34) described elastic-muscular sys- 

 tems in the large veins of the cow, similar to the 

 tension muscles described by Benninghoff (10, 11). 

 However, v. Kiigelgen (47, 49) could never find such 

 tension muscles in human veins. He described, rather, 

 muscles like the arterial ring muscles, the individual 

 muscle cells being connected together as a network. 

 This network of smooth muscles is tied to the collagen 

 fibers and the intima. 



Figure 14 shows the percentages of smooth muscles 

 and collagen and elastic fibers in different human 

 veins. The smooth muscles are separately graphed as 

 transverse (circular) and longitudinal muscles. The 

 longitudinal muscles of the veins are not arranged 

 in bundles in the intima, as are those of the arteries. 

 Rather, they form a network in the wall with the 

 circular muscles, the smooth muscles being either 

 longitudinal or transverse, or at any other angle. 



The circular muscles are mainly in the veins of 

 the leg, whereas the longitudinal muscles predomi- 

 nate in the abdominal veins. Figure 1 5 shows that 

 the proportion of circular muscles parallels the 

 pressure in the veins in the erect posture, there then 

 being considerable hydrostatic pressure in the human 

 leg veins. Since the wall tension in a tube, in the 

 transverse direction, is twice that in the longitudinal 

 direction [Frank (30)], the percentages of circu- 

 lar muscles are higher in veins subject to higher 

 pressures. Hydrostatic pressure and wall tension vary 

 with posture; therefore this variable pressure load 

 can be supported better by muscles capable of 

 myogenic activity, as in arteries, than by collagen or 

 elastic tissues (see above). Along with the higher 

 amount of smooth muscles in the leg veins the 

 relationship of radius to wall thickness is less than that 

 of other veins [v. Kiigelgen (48)]. Veins of the thorax, 



