The fine structure of the arteriovenous anastomosis and its nerve supply in the human nasal respiratory mucosa.код для вставкиСкачать
The Fine Structure of the Arteriovenous Anastomosis and Its Nerve Supply in the Human Nasal Respiratory Mucosa ' NIKOLAJS CAUNA (WITH TECHNICAL ASSISTANCE OF AGNES CRALLEY) Department of Anatomy and Cell Biology, T h e School of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania I521 3 ABSTRACT The fine structure of the arteriovenous anastomosis was investigated i n the normal human nasal mucosa. The tissues were fixed i n 2% osmic acid solution, embedded in Epon and stained with uranyl acetate and lead citrate solutions. It was found that the endothelial basement membrane of the arterial segment of the anastomosis was discontinuous. The anastomosing artery possessed subendothelial cushions of longitudinal smooth musculature which expanded into a thick uniform layer before the artery joined the vein. The fine morphology of these muscle cells did not show epitheloid modification. An elastic membrane of a peculiar structure separated the subendothelial musculature from that of the tunica media. The membrane was continuous with the internal elastic membrane of the proximal artery and with the adventitial elastic mesh of the vein. The anastomosis was supplied by a non-myelinated periarterial nerve plexus which contained cholinergic and adrenergic axons characterized by agranular and fine granular vesicles respectively. The wall of the vein was devoid of musculature and nerves. It mainly consisted of elastic meshes interspersed with bundles of collagen fibers and occasional fibrocytes. It was suggested that the musculature of the tunica media of the artery was controlled by the cholinergic and adrenergic nerves of the autonomic system, and by the sensory nerves in the form of axons reflexes. The subendothelial musculature was controlled by agents carried in blood and was not influenced by the adventitial nerves. The blood vessels of the nose regulate the and is an extension of earlier investigations size of the nasal passages and are involved in this series (Cauna, '70; Cauna et al., in the humidification and thermal adjust- '69; Cauna and Hinderer, '69). ment of the inhaled air. The vascular bed MATERIAL AND METHODS expands and contracts rhythmically probably due to the activities of the arterioThe material used in this study was obvenous anastomoses (Clark and Clark, tained during corrective surgery of the nose '34). The vessels react vividly to various under block anesthesia with 2% Xplokinds of environmental stimuli, drugs and caine @ solution. 'Tissues came from seven emotional conditions. They appear to be male and three female patients ranging in under sympathetic and parasympathetic age from 16 to 48 years. They were fixed control (Malcomson, '59). The existence in 1% osmic acid solution in phosphate of the arteriovenous anastomoses in the buffer, embedded in Epon 812 and stained human nose was denied as recently as 30 with uranyl acetate and lead citrate soluyears ago (Korner, '37). Subsequent work- tions (Cauna et al., '69). All illustrations in ers, however, demonstrated these struc- this paper were taken from the septal mutures beyond dispute (Mark, '41; Fabbi cosa dorsal to the ~UCO-cutaneous junction and Rossatti, '51; TemesrkkBsi, '69). Ros- of a male patient 46 years old. satti ('54) further suggested that the orOBSERVATIONS ganization and function of the anastomoses were different in the erectile tissue over The arteriovenous anastomoses were frethe conchae and in the septal mucosa quently encountered in the deeper layer of which did not possess true cavernous si- the nasal lining, usually near the nasal nuses. The present work is part of a correReceived Feb. 9. '70. Accewted Awr. 8 , '70. lative study of the fine morphology, histo1 This study was supported by Public Health Service chemistry and functions of the nasal lining grant NB 04147. ANAT.REC., 168: 9-22. 9 10 NIKOLAJS CAUNA glands. The anastomosing vessels were tortuous to a varying degree. Sometimes they resembled simple glomeruli, but they were devoid of distinct fibrous capsules. The anastomosing arteries were characterized by the appearance in their walls of fascicles of longitudinal smooth muscle cells located between the endothelial lining and the internal elastic membrane ( M in fig. 1). Nearer the anastomosis, the subendothelial Fig. 1 Transverse section of a n artery near its tmastomosis with the vein. Its tunica intima has acquired an incomplete layer of longitudinal smooth muscle fibers ( M ) located between the internal elastic membrane (El) and the endothelium (cf. with M in fig. 2 ) . Tm, tunica media; G, acinus of a nasal gland. Osmium fixed tissue embedded in Epon, 1 p thick section stained with toluidine blue solution. x 400. Fig. 2 Transverse section of the arteriovenous anastomosis. M, longitudinal subendothelial smooth muscle cell layer (cf. with M in fig. 1). El, elastic membrane, continuous with the internal elastic membrane of the proximal segment of the artery (cf. with El in fig. 1); Tm, tunica media ending at h, a short distance before the junction with the vein (V). Osmium fixed tissue embedded in Epon, 1 p thick section stained with toluidine blue solution. X 400. FINE STRUCTURE OF ARTERIOVENOUS ANASTOMOSIS musculature became thick and uniformly distributed around the lumen of the artery (M in fig. 2). The transition of the thick walled artery into the thin walled vein was abrupt ( V in figs. 2, 8). Both segments showed unusual fine morphology. The arterial segment appeared to possess a dual nerve supply. The arterial segment The arterial segment possessed a closed endothelial lining which was supported externally by a discontinuous basement membrane. The latter filled the wide interval between the endothelial tube and the longitudinal muscle cell layer and had the appearance of a loose network which was traversed by large and irregular passages (BM i n fig. 3 ) . 11 The subendothelial muscle cells were loosely arranged ( m in figs. 4, 5). The intervals usually contained collagen fibers of longitudinal orientation ( A i n fig. 4 ) . The cells that were nearest to the tunica media were also spaced by extensions of the elastic membrane and by occasional fibrocytes (Lam and F in fig. 5). All muscle cells appeared to be interconnected across the spaces by appositional junctions (Jc in fig. 4). Their basement membrane was thick and formed a continuous system extending from cell to cell over the junctional areas (bm i n fig. 4 ) . Only the luminal aspects of the innermost muscle cells were devoid of it, and were related to the modified basement membrane of the endothelial tube (cf. bm and BM in fig. 3 ) . Fig. 3 Tunica intima of the arterial segment of the anastomosis. L, lumen; End, endothelial cell; EM, zone of the modified endothelial basement membrane; m, subendothelial muscle cell; bm, basement membrane of the subendothelial musculature. ?: 25,000. 12 NIKOLAJS CAUNA Fig. 4 Subendothelial smooth muscle cells ( m ) spaced by intervals (A) and interconnected by appositional junctions (Jc) ; bm, basement membrane system of the musculature. X 20,000. The elastic membrane that separated the subendothelial musculature from the tunica media was found to be a continuation of the internal elastic membrane of the artery that gave rise to the anastomosis (cf. El in figs. 1, 2). Distally the membrane became continuous with the adventitial elastic mesh of the vein (el. in figs. 8 , 10). The arterial elastic membrane had a characteristic fine structure (El in fig. 5). Its outer zone consisted of a continuous elastic lamella, while the inner zone contained fine branching elastic fibers. The latter were finest on the innermost aspect of the membrane (cf. El and el in fig. 6). The inner zone also contained collagen fibers, microfibrils and some peculiar fluted fibers that were not observed elsewhere (unlabelled arrows in fig. 6 ) . Scattered throughout the elastic membrane and its continuation into the wall of the vein were electron dense spherical granules ranging from approximately 200 A to 0.5 in diameter ( G in figs. 5 , 6 , 7, 10). They showed an irregular grainy substructure under high magnification both in stained and unstained sections. The external surface of the elastic membrane facing the tunica media was smooth; that facing the subendothelial musculature appeared uneven and was frequently laminated. Some laminae extended into the subendothelial musculature for a considerable distance (Lam in fig. 5). On approaching the junction between the artery and the vein, the elastic membrane underwent a gradual change. The outer elastic lamina became progressively thinner and fragmented (El in fig. 7), and it disappeared altogether without reaching the vein. The inner zone of the FINE STRUCTIJRE OF ARTERIOVENOUS ANASTOMOSIS 13 Fig. 5 Elastic membrane ( E l ) of the arterial segment of the arteriovenous anastomosis located between the tunica media (Media) and the subendothelial smooth muscle cells ( m ) . G , granules in the elastic membrane; Lam, elastic lamina extending into the subendothelial muscle cell layers; F, part of a fibrocyte. ?< 12,000. 14 NIKOLAJS CAUNA Fig. 6 Segment of the elastic membrane (cf. with El in fig. 5 ) . The outer zone consists of a continuous elastic lamina (El), the inner zone contains fine elastic fibers (el), collagen (Col) and fine fibrils (Fib). Some fibers (unlabelled arrows) that mingle with the collagen appear deeply scalloped i n transverse sections; G , granules i n the elastic rncmbrane; F, process of a fibrocyte external to the elastic membrane. 40,000. FINE STRUCTURE O F ARTERIOVENOUS ANASTOMOSIS 15 Fig. 7 Segment of the arterial elastic membrane close to the arteriovenous junction. The outer elastic lamina ( E l ) is disappearing, the inner zone of fine elastic fibers (el) becomes wider and extends into the wall of the vein (cf. with figs 8-10). G, granule in the membrane; m, subendothelial muscle cell; F, process of a fibrocy te. >: 20,000. fine elastic fibers became wider and extended into the vein where it formed the outer one half of its wall1 (figs. 8, 10). The tunica media of the anastomotic artery mainly consisted of smooth muscle cells arranged in compact concentric layers (Tm in figs. 1, 2 ) . The basement membrane system of the musculature was well developed. Some elastic fibers coursed between the muscle cells, but an external elastic membrane was absent. The circular muscle cell layer ended about 1 0 0 p short of the junction between the artery and the vein thus exposing the modified elastic membrane of the artery to the adventitia (asterisk in fig. 2, cf. with el in fig. 8). The tunica adventitia of the artery contained fibrocytes, some elastic fibers of irregular arrangement and loose collagen bundles which supported a number of vasa vasorum and fascicles of non-myelinated nerves. The venous segment The structure of the thin walled vein was basically different from that of regular veins. The tunica intima consisted of a closed endothelial tube supported externally by a basement membrane of regular appearance (End and BM in fig. 9). The rest of the wall was characterized by a total absence of musculature and a near absence of other cellular elements (figs. 8, 9, 10). The inner portion of the wall consisted of a fine mesh of matted elastic fibers mingled with fascicles of collagen fibers of varying orientation (el and Col in fig. 9). Towards the adventitia, the elastic fibers became coarser while the collagen component disappeared. The outer layer of the wall consisted of an elastic mesh which was a direct continuation of the inner zone of the arterial elastic membrane. Like the latter, it contained spherical granules (G in fig. 1 0 ) scattered among the fiber fascicles. 16 NIKOLAJS CAUNA Fig. 8 Arteriovenous junction (cf. with V in fig. 2). L, lumen; m, subendothelial smooth muscle cells of the artery; el, modified elastic membrane continuous from the artery into the vein (V). El, elastic fibers external to the vessel wall. ~4,000. The nerve su p p ly All nerves of the arteriovenous anastomosis were non-myelinated and were located in the adventitia of the arterial segment. They never penetrated into the tunica media. The subendothelial muscle cell layer was devoid of nerves. The axons were of the beaded variety. Their narrow segments were closely enwrapped by the Schwann sheath and usually showed few morphologically defined axoplasmic components except for some fibrillar or tubular elements. The enlarged segments of the axons were partly covered by the Schwann cell cytoplasm and partly exposed to the intercellular space and the musculature of the blood vessels. The axolemma of the exposed parts of the axons, however, showed no apparent morphological specialization. and its external aspect was covered with the basement membrane of the nerve (figs. 11, 12, 13). Their axoplasm contained mitochondria, glycogen granules, and occasional vacuoles (figs. 11-13). In addition, the axons contained accumulations of microvesicles. Over the proximal segment of the anastomosis, such as shown in figure 1, some axons only contained agranular vesicles that usually characterize cholinergic nerves (fig. 12). Others contained a FINE STRUCTURE OF ARTERIOVENOUS ANASTOMOSIS 17 Figs. 9-10 Luminal and adventitial portions of the wall of the vein (cf. with V in fig. 8 ) . L, lumen; End, endothelial cell; BM, endothelial basement membrane; Col, twisting bundles of collagen fibers; el, bundles of fine elastic fibers; G, granule in the adventitial elastic mesh; Adv, adventitial surface of the vein. x 20,000. 18 NIKOLAJS CAUNA mixture of agranular and small granular vesicles (arrows in fig. 11) as encountered in adrenergic nerves (Grillo, '66; Hokfelt, '68). In the immediate vicinity of the arteriovenous junction, there were fewer adventitial nerves. The fascicles were smaller and usually were closely related to the vasa vasorum of the artery (fig. 13). The latter contained a layer of smooth muscle cells around the periphery of their endothelial tubes ( m in fig. 13). The axons of the related nerves only contained accumulations of small agranular vesicles and were exposed to the muscle cells (arrows in fig. 13). DISCUSSION The arteriovenous anastomosis has a typical fine morphology which is differsnt from that of the regular arteries and veins of the same caliber. Its most conspicuous feature is the longitudinal smooth musculature which produces subendothelial cushions i n the proximal segment of the artery and expands into a thick uniform layer before the artery joins the vein (figs. 1, 2 ) . According to Clara ('39), the longitudinal muscle cells undergo epithelioid modification in certain kinds of anastomoses. Mark ('41) and Rossatti ('54) using the optical microscope state that the anastomoses of the human nose contain epithelioid cells as defined by Clara, whereas Temesrekasi ('69 1 has the opposite view. Dawes and Prichard ('53) find that the musculature of the anastomotic artery in the nose of the cat and dog partly consists of smooth muscle cells and partly of the epithelioid type. In the present material, the cells in question have the characteristics of smooth muscle fibers and cannot be distinguished from the muscle cells of the tunica media on a morphological basis (figs. 3-5, 7, 8, cf. with m i n fig. 12). However, histochemically the muscle cells exhibit butyrocholinesterase activity not observed in the musculature of the regular nasal blood vessels (Cauna et al., '69). According to Luckner ('55) the subendothelial cells also contain acetylcholine at least in the glomus organ. The specialized muscle cells may have other histochemical properties that are not recognized morphologically. The porosity of the endothelial basement membrane is one of the characteristics of the nasal blood vessels (Cauna and Hinderer, '69). As a result of this condition. the subendothelial musculature of the vessels, including that of the anastomosing artery may readily be influenced by agents carried i n the blood (fig. 3 ) . This finding may explain clinical and experimental observations that the nasal blood vessels are particularly sensitive to drugs introduced through the blood stream (Sherman, '63; Stovall and Jackson, '67). Experimental studies also show that the arteriovenous anastomoses are particularly sensitive to changes in blood composition such as hypoxia (Luckner, '55) and variations in the pH values (Walder, '52). The elastic membrane separates the subendothelial musculature from the muscle layer of the tunica media and from the nerves that are located in the tunica adventitia (El in fig. 5 ) . The musculature of the tunica media and the vasa vasorum of the artery are probably controlled by the periarterial nerve plexus. Experimental and clinical evidence suggests that the cholinergic fibers of the nasal blood vessels are derived from the greater petrosal nerve and the sphenopalatine ganglion, while the adrenergic ones from the superior cervical ganglion (Malcomson, '59). The occurrence of a dual nerve supply is confirmed by the present morphological findings (figs. 11-13). There are no specialized contact areas between the axons of the adventitial nerves and the muscle cells. Therefore, the nervous control is probably effected indirectly by active agents that are released from the nerves into the perivascular space. These would reach the muscle cells of the tunica media by diffusion. The subendoFig. 11 Non-myelinated nerve cut transversely from the adventitia of the artery shown in figure 1. The four axons contain mitochondria, vacuoles (Vc), glycogen granules and two kinds of microvesicles. The majority of the latter appear agranular while others are granular (arrows). S , Schwann cell; bm, basement membrane of the nerve. x 60,000. Fig. 12 Part of a non-myelinated nerve from the adventitia of the same artery as in figure 11. The axon (Ax) is partly enwrapped by Schwann cell ( S ) and partly exposed towards the muscle cell ( m ) of the tunica media. The interval contains the basement membranes of the nerve and the muscle cell (Bm), some fibers and a process of a fibrocyte (F). The axoplasm of the ending is filled with agranular vesicles, typical of cholinergic nerves. y 40,000. FINE STRUCTURE OF ARTERIOVENOUS ANASTOMOSIS Figures 11-12 19 20 NIKOLAJS CAUNA Fig. 13 Part of a vas vasorum ( V ) and a related nerve from the adventitia of the arteriovenous anastomosis (see fig. 2). The vessel possesses musculature ( m ) . The two axons (arrows) contain agranular vesicles. They are partly enwrapped by the Schwann cell ( S ) and partly exposed towards the musculature of the vessel; bm, basement membrane, cut tangentially over the surface of the muscle cell. x 40,000. thelial musculature that is located on the luminal aspect of the elastic membrane would probably not be influenced by these agents because of the distances involved and because the elastic lamina may constitute an effective permeability barrier. The nerves that are found in abundance in the adventitia of the arterial segment may not all be autonomic. Sensory nerves proceed to the surface along with the arteries and veins. In the respiratory area of the nose, these nerves are non-myelinated; they exhibit acetylcholinesterase activity and contain accumulations of agranular vesicles in their axoplasm (Cauna et al., ’69). These apparently “cho- FINE STRUCTURE OF ARTEIRIOVENOUS ANASTOMOSIS linergic" sensory nerves may affect the activity of the nasal vessels including the arteriovenous anastomoses by means of axon reflexes (Cauna, "70). Experimental studies with the anastomoses strongly suggest such a possibility (Grant, '29). While the control mechanism of the arterial segment of the anastomosis appears to be remarkably complex, none can be recognized in the thin walled vein. The latter is devoid of musculature and its adventitia is devoid of nerves. The elastic wall of the vein, however, appears to be well designed to receive blood at varying pressure levels. ACKNOWLEDGMENTS The author wishes to thank Dr. Kenneth H. Hinderer for the supply of the samples of the human nasal respiratory mucosa and Mr. Charles Abbott for his aid with the photographic work. LITERATURE CITED Cauna, N. 1970 Electron microscopy of the nasal vascular bed and its nerve supply. 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