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Ultrastructure of renal arterial vessels with special reference to elastic tissue content
Micron, 1976, Vol. 7: 257-264. Pergamon Press. Printed in Great Britain.
U l t r a s t r u c t u r e o f renal arterial v e s s e l s w i t h special reference to elastic t i s s u e content R. D. BELL, J. A. N O R D Q U I S T , A. K. MANDAL* and C. L. RODGERS
Research Service, Veterans Administration Hospital, and Departments of Medicine and Urology, University of Oklahoma College of Medicine, Oklahoma City, Oklahoma 73190, U.S.A. Manuscript received March 1976; revised July 8, 1976 Renal cortical tissue Jrom normal Wistar rats was studied by electron microscopy for arterial vessels. The tissue was fixed in 4°//o glutaraldehyde, post-fixed im 1% osmium tetroxide and embedded in Spurr's embedding medium. When an arterial vessel was found, ultra-thin (,~30nm) sections were cut, stained with uranyl acetate and lead citrate, periodic acid with silver methenamine or silver tetraphenyl prophyrin sulphonate. Three types of arterial cessels were recognized: small artery, large arteriole and small arteriole. Each type demonstrated three layers consisting of endothelial cells, basement membrane and snwoth muscle cells. The basement membrane with variable contents of elastic tissue appears to be the most valuable parameter for differentiating arterial vessels of different size. The proportion of elastic tissue in the basement membrane decreases in the following order: artery, large arteriole and small arteriole. Thus, a small artery has a thin basement membrane containing bulk elastic tissue; in contrast, a small arteriole has a more conspicuous basement membrane containing much less elastic tissue. In large arterioles, the basement membrane is of intermediate thickness and elastic tissue content. The concept of an 'internal elastic lamina' as a definitive layer qf arterial vessels could not be supported by the results of this study.
INTRODUCTION Numerous investigators have described the structure of arterial vessels using light microscopy. In histological sections, the differences among the various types of arterial vessels e.g. large artery, small artery and large or small arteriole, could not be readily recognized. An arbitrary size of the vessel has been used by m a n y as the criterion for distinguishing a small artery from a large or small arteriole (Leeson and Leeson, 1970; H a m and Leeson, 1961; Heptinstall, 1954). Attempts have been made to resolve this controversial issue by studying arterial vessels with the aid of the electron microscope (Moore and Ruska, 1957; Movat and Fernando, 1963 ; Fernando and Movat, 1964). Ultrastructural studies by these investigators demonstrated that an artery can be distinguished from a large or small arteriole by the amount of elastic tissue and number of layers of smooth muscle cells. The present study proposes a new method of distinguishing between small arteries
*Recipient of Veterans Administration Career Development Award.
and arterioles, and between large and small arterioles, based on the thickness of the basement m e m b r a n e (BM) intervening between endothelial cells and smooth muscle cells, and the amount of elastic tissue present within the BM. MATERIALS AND METHODS Renal cortical tissue from normal Wistar rats was fixed in 40/0 iced glutaraldehyde, post-fixed in 1 °/o osmium tetroxide, dehydrated in alcoholic solutions and propylene oxide and embedded in Spurr's low viscosity embedding medium. From the blocks, thick sections were cut, stained with methylene blue and azure 11 and examined with the light microscope. When an arterial vessel was found, the block was prepared for study by electron microscopy. Ultra-thin ( ~ 3 0 n m ) sections were cut and collected on copper and gold grids. Sections mounted on the copper grids were stained with uranyl acetate and lead citrate (UA + LC). Some of those mounted on the gold grids were stained with 1% periodic acid and methenamine silver (PASI) according to the technique described by Olson et al. (1967). Others were
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258
R. t). Bell, .]. A. Nordquist, A. K. Mandal and C. L. Rodgers
stained with silver tetraphenyl prophyrin sulphonate (STPPS) which specifically increases the density of elastic tissue. T h e STPPS technique was first described by Albert and Fleischer (1970) and modified in the author's laboratory (Nordquist et al., 1975). All the grids were studied by an E M U 3F (RCA) electron microscope. RESULTS Three types of arterial vessels were recognized: small artery, large arteriole and small arteriole.
Small artery
Figur~ 1 (UA + LC) shows endothelial compression and a broad convoluted electronlucent band intervening between the endothelial cells and smooth muscle cells. A thin, somewhat electron-opaque, m e m b r a n e is seen lining the electron-lucent band along both endothelial and smooth muscle cellular (SMC) layer. The medial layer consists of two or more layers of smooth muscle cells (SMC). T h e y are relatively large but cytoplasmic organdies are sparse. A basement m e m b r a n e (BM) containing variable amounts of electron-lucent material separates individual SMC and surrounds the outer
Fig. 1. A small artery shows broad electron-lucent band of elastic tissue (EL) and thin stripes of basement membrane (arrows) at inner and outer parts. END, endothelial cell; L, lumen ; SMC, smooth muscle ceil. UA %- LC × 28,000.
Ultrastructure of Renal Arterial Vessels border. Figure 2 (STTPS) demonstrates a broad band of electron-dense elastic tissue which corresponds to the electron-lucent band seen in Fig. 1 (UA 4- LC). A thin electron-lucent membrane on inner and outer aspects of the central electron-dense band can be conspicuously separated from the endothelial and SMC layers respectively (Insert, Fig. 2). Electrondense elastic tissue is also found within the BM at the perimeter of the vessel.
Large arteriole In this arteriole (Fig. 3), endothelial cells are
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less conspicuous and the BM is single-layered with complete absence of the homogeneous electron-lucent band seen in the small artery. Instead, thin masses of electron-lucent material are found within the BM. The BM is irregularly convoluted, but the undulations are inconspicuous. SMC usually form 2-4 layers. They are separated from each other by an electronopaque, but thinner, BM and they appear to be active, since they have many mitochondria, ribosomes and an endoplasmic reticulum. PASI (Fig. 4) demonstrates uniform electron-opacity of the BM and deposits of silver within the
Fig. 2. This small artery (the same as in Fig. 1) exhibits electron-dense elastic tissue in the centre, and thin stripes of electron-lucent basement membrane (arrows) at the inner and outer parts. END, endothelial cell; SMC, smooth muscle cell; L, lumen. STPPS x 30,000° Insert: Part of the same artery at higher magnification showing the materially dense elastic tissue (EL) bordered on both sides by lighter areas (arrows) of the basement membrane. STPPS. x 62,000.
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R.D. Bell, J. A. Nordquist, A. K. Mandal and C. L. Rodgers
Fig. 3. A large arteriole reveals small electron-lucent elastic tissue (circles) in the basement membrane (BM). Many mitochondria, ribosomes and Golgi complex (C) are seen in the smooth muscle cell (SMC). L, lumen. UA ~- LC. ×23,000.
membrane. The presence of many mitochondria in the smooth muscle cells provides further evidence for the possible activity of these cells in the large arteriole. STPPS staining (Fig. 5) reveals three distinct layers in the BM between the endothelial cells and SMC. From inner to outer layer, they are electron-lucent, electrondense and electron-lucent. Short, thin strips of electron-dense elastic tissue may be found at the outer border.
Small arteriole As shown in Fig. 6 (UA + LC) endothelial cells tend to be compressed and a convoluted BM is observed between the endothelial and SMC layers. A small amount of an electronlucent material can be seen within the BM, The smooth muscle cells form a continuous single layer and demonstrate small nuclei, few organelles and a poorly differentiated outer border, the latter merging imperceptibly into
Ultrastructure of Renal Arterial Vessels
261
Fig. 4. A large arteriole shows fine deposits of silver in the basement membranes (BM) and cytoplasmic continuity (arrows) between adjacent smooth muscle cells (SMC). Many mitochondria are seen in the SMC. L, lumen. PASI. × 31,000. the interstitium. Figure 7 (PASI) confirms that the convoluted structure is BM. The m e m b r a n e is argyrophilic throughout and almost completely lacks any electron-lucent material. STPPS staining reveals small bands of electrondense elastic tissue within the BM. No electrondense material is found at the outer border of this size vessel. DISCUSSION This ultrastructural study of renal arterial vessels utilizing several staining techniques characterizes three types of small arterial vessels.
T h e y are small artery, large arteriole and small (terminal) arteriole. Each vessel type exhibits three layers: endothelial, basement m e m b r a n e and medial (smooth muscle cell) layer. T h e endothelial cells and layers of smooth muscle cells are of little value in differentiating between the vessels under study. Smooth muscle cells (SMC) appear to differ, however, in that those of the artery are relatively large with comparatively few organelles while those of the large arteriole are generally smaller and apparently more active, with m a n y mitochondria and other organelles. The SMC in the small arterioles are single layered and generally
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R.D. Bell, J. A. Nordquist, A. K. Mandal and C. L. Rodgers
Fig. 5. A large arteriole reveals electron-dense elastic tissue in the centre of the basement membrane bordered by thick stripes of electron-lucent material (arrows). END, endothelial cells; SMC, smooth muscle cell. STPPS. 5<27,500.
lacking in intracellular organelles. The basement membrane (BM) is characterized by argyrophilia (Walker, 1973), but the BM elastic tissue content (demonstrated by STPPS staining) appears to be the most valuable parameter for differentiating the various types of arterial vessel. Movat and Fernando (1963), have emphasized the value of using the presence or absence of the 'internal elastic lamina' as an important criterion for distinguishing arteries from arterioles. Small arteries are reported to have an internal elastic lamina, while this structure is absent from the small or 'terminal arterioles'. Spiro et al. (1965) suggested that the number of SMC layers could be used to differentiate between large and small arterioles. However, this is not supported by the present study. O n the other hand, the present study has shown that the BM of different sized vessels contains
variable amounts of elastic tissue which decrease in proportion to the size of the vessel. Thus, a small artery contains large amounts of' elastic tissue while a small arteriole has only a small amount of this substance. It is of special interest that the present study has demonstrated elastic tissue in even the smallest of renal arteriolar vessels. These vessels are extremely effective in altering resistance to blood flow and require elastic tissue as well as SMC for graded contraction (Burton, 1966). Acknowledgements--The authors wish to express gratitude to Dr. Marc A. Pfeffer and Mrs. Janice M. Pfeffer, Department of Medicine, Jarvard Medical School (formerly of the Department of Medicine, University of Oklahoma College of Medicine) for providing the kidneys from Wistar rats for this study. The authors are grateful to Ms. Carolyn Clay, secretary, for typing and editing the revised manuscript.
Ultrastructure of Renal Arterial Vessels
263
Fig. 6. A small arteriole exhibits a convoluted basement membrane (BM) with inconspicuous quantities of electron-lucent elastic tissue (arrows). END, endothelial cell; SMC, smooth muscle cell; L, lumen. Free interstitium (I) and tubule (T) are also shown. UA + LC. X 18,000.
REFERENCES Albert, E. N. and Fleischer, E., 1970. A new electrondense stain for elastic tissue. J. Hostochem. Cytochem., 18: 697-708. Burton, A. C., 1966. Walls of the blood vessels and their function. In: Physiology and Biophysics of the Circulation. Yearbook Medical Publishers, Chicago, U.S.A., 72~33. Fernando, N. V. P. and Movat, H. Z., 1964. I. The smallest arterial vessels: Terminal arterioles and metarterioles. Exp. Mol. Path., 3: 1-9. Ham, A. W. and Leeson, T. S., 1961. Histology. Lippincott, Philadelphia.
Heptinstall, R. H., 1954. Renal biopsies in hypertension. Br. HeartaT. 16: 133-141. Leeson, T. S. and Leeson, C. R., 1970. The circulatory system. In: Histology, W. B. Saunders, Philadelphia, U.S.A., 215-233. Moore, D. H. and Ruska, H., 1957. The fine structure of capillaries and small arteries, a7. Biophys. Biochem. Cytol., 3: 457-462. Movat, H. Z. and Fernando, N. V. P., 1963. The fine structure of the terminal vascular bed. I. Small arteries with an internal elastic lamina. Exp. Mol. Path., 2: 549-563.
264
R. 1). Bell..l.A. Nordquist. A. K. Mandal and C. L. Rodgers
Nordquist, J. A., Chrysant, K., and Mandal, A. K., 1975. A modified technique of staining elastic tissue tbr electron microscopic study. In: Proc. 33rd Annual Meeting EII/ISA, Las Vegas, Nevada, Bailey, G. W. (ed.), 626-627. Olson, R. L., Nordquist, J. A. and Everett, M. A., 1967. Lysosomes and the skin. In: Proc. 13th Internat. Congr. Dermatology, Munich, Jadasson, W.
and Schiren, C. (eds.), Springer--Verlag, Berlin, 1056-1060. Spiro, D., Lattes, R. G. and Wiener, J., 1965. l'hc cellular pathology of experimental hypertension. Am. J. Path. 47: 19-49. Walker, F., 1973. The origin, turnover, and removal of glomerular basement membrane. J. Path., 110: 233-244.
Fig. 7. The identity of the basement membrane (BM) in the small arteriole is confirmed by its argyrophilia. Mitochondria and lipid droplets (LI) can be seen in the smooth muscle cell. (SMC). L, lumen. PASI. × 32,000.
U l t r a s t r u c t u r e o f renal arterial v e s s e l s w i t h special reference to elastic t i s s u e content R. D. BELL, J. A. N O R D Q U I S T , A. K. MANDAL* and C. L. RODGERS
Research Service, Veterans Administration Hospital, and Departments of Medicine and Urology, University of Oklahoma College of Medicine, Oklahoma City, Oklahoma 73190, U.S.A. Manuscript received March 1976; revised July 8, 1976 Renal cortical tissue Jrom normal Wistar rats was studied by electron microscopy for arterial vessels. The tissue was fixed in 4°//o glutaraldehyde, post-fixed im 1% osmium tetroxide and embedded in Spurr's embedding medium. When an arterial vessel was found, ultra-thin (,~30nm) sections were cut, stained with uranyl acetate and lead citrate, periodic acid with silver methenamine or silver tetraphenyl prophyrin sulphonate. Three types of arterial cessels were recognized: small artery, large arteriole and small arteriole. Each type demonstrated three layers consisting of endothelial cells, basement membrane and snwoth muscle cells. The basement membrane with variable contents of elastic tissue appears to be the most valuable parameter for differentiating arterial vessels of different size. The proportion of elastic tissue in the basement membrane decreases in the following order: artery, large arteriole and small arteriole. Thus, a small artery has a thin basement membrane containing bulk elastic tissue; in contrast, a small arteriole has a more conspicuous basement membrane containing much less elastic tissue. In large arterioles, the basement membrane is of intermediate thickness and elastic tissue content. The concept of an 'internal elastic lamina' as a definitive layer qf arterial vessels could not be supported by the results of this study.
INTRODUCTION Numerous investigators have described the structure of arterial vessels using light microscopy. In histological sections, the differences among the various types of arterial vessels e.g. large artery, small artery and large or small arteriole, could not be readily recognized. An arbitrary size of the vessel has been used by m a n y as the criterion for distinguishing a small artery from a large or small arteriole (Leeson and Leeson, 1970; H a m and Leeson, 1961; Heptinstall, 1954). Attempts have been made to resolve this controversial issue by studying arterial vessels with the aid of the electron microscope (Moore and Ruska, 1957; Movat and Fernando, 1963 ; Fernando and Movat, 1964). Ultrastructural studies by these investigators demonstrated that an artery can be distinguished from a large or small arteriole by the amount of elastic tissue and number of layers of smooth muscle cells. The present study proposes a new method of distinguishing between small arteries
*Recipient of Veterans Administration Career Development Award.
and arterioles, and between large and small arterioles, based on the thickness of the basement m e m b r a n e (BM) intervening between endothelial cells and smooth muscle cells, and the amount of elastic tissue present within the BM. MATERIALS AND METHODS Renal cortical tissue from normal Wistar rats was fixed in 40/0 iced glutaraldehyde, post-fixed in 1 °/o osmium tetroxide, dehydrated in alcoholic solutions and propylene oxide and embedded in Spurr's low viscosity embedding medium. From the blocks, thick sections were cut, stained with methylene blue and azure 11 and examined with the light microscope. When an arterial vessel was found, the block was prepared for study by electron microscopy. Ultra-thin ( ~ 3 0 n m ) sections were cut and collected on copper and gold grids. Sections mounted on the copper grids were stained with uranyl acetate and lead citrate (UA + LC). Some of those mounted on the gold grids were stained with 1% periodic acid and methenamine silver (PASI) according to the technique described by Olson et al. (1967). Others were
257
258
R. t). Bell, .]. A. Nordquist, A. K. Mandal and C. L. Rodgers
stained with silver tetraphenyl prophyrin sulphonate (STPPS) which specifically increases the density of elastic tissue. T h e STPPS technique was first described by Albert and Fleischer (1970) and modified in the author's laboratory (Nordquist et al., 1975). All the grids were studied by an E M U 3F (RCA) electron microscope. RESULTS Three types of arterial vessels were recognized: small artery, large arteriole and small arteriole.
Small artery
Figur~ 1 (UA + LC) shows endothelial compression and a broad convoluted electronlucent band intervening between the endothelial cells and smooth muscle cells. A thin, somewhat electron-opaque, m e m b r a n e is seen lining the electron-lucent band along both endothelial and smooth muscle cellular (SMC) layer. The medial layer consists of two or more layers of smooth muscle cells (SMC). T h e y are relatively large but cytoplasmic organdies are sparse. A basement m e m b r a n e (BM) containing variable amounts of electron-lucent material separates individual SMC and surrounds the outer
Fig. 1. A small artery shows broad electron-lucent band of elastic tissue (EL) and thin stripes of basement membrane (arrows) at inner and outer parts. END, endothelial cell; L, lumen ; SMC, smooth muscle ceil. UA %- LC × 28,000.
Ultrastructure of Renal Arterial Vessels border. Figure 2 (STTPS) demonstrates a broad band of electron-dense elastic tissue which corresponds to the electron-lucent band seen in Fig. 1 (UA 4- LC). A thin electron-lucent membrane on inner and outer aspects of the central electron-dense band can be conspicuously separated from the endothelial and SMC layers respectively (Insert, Fig. 2). Electrondense elastic tissue is also found within the BM at the perimeter of the vessel.
Large arteriole In this arteriole (Fig. 3), endothelial cells are
259
less conspicuous and the BM is single-layered with complete absence of the homogeneous electron-lucent band seen in the small artery. Instead, thin masses of electron-lucent material are found within the BM. The BM is irregularly convoluted, but the undulations are inconspicuous. SMC usually form 2-4 layers. They are separated from each other by an electronopaque, but thinner, BM and they appear to be active, since they have many mitochondria, ribosomes and an endoplasmic reticulum. PASI (Fig. 4) demonstrates uniform electron-opacity of the BM and deposits of silver within the
Fig. 2. This small artery (the same as in Fig. 1) exhibits electron-dense elastic tissue in the centre, and thin stripes of electron-lucent basement membrane (arrows) at the inner and outer parts. END, endothelial cell; SMC, smooth muscle cell; L, lumen. STPPS x 30,000° Insert: Part of the same artery at higher magnification showing the materially dense elastic tissue (EL) bordered on both sides by lighter areas (arrows) of the basement membrane. STPPS. x 62,000.
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R.D. Bell, J. A. Nordquist, A. K. Mandal and C. L. Rodgers
Fig. 3. A large arteriole reveals small electron-lucent elastic tissue (circles) in the basement membrane (BM). Many mitochondria, ribosomes and Golgi complex (C) are seen in the smooth muscle cell (SMC). L, lumen. UA ~- LC. ×23,000.
membrane. The presence of many mitochondria in the smooth muscle cells provides further evidence for the possible activity of these cells in the large arteriole. STPPS staining (Fig. 5) reveals three distinct layers in the BM between the endothelial cells and SMC. From inner to outer layer, they are electron-lucent, electrondense and electron-lucent. Short, thin strips of electron-dense elastic tissue may be found at the outer border.
Small arteriole As shown in Fig. 6 (UA + LC) endothelial cells tend to be compressed and a convoluted BM is observed between the endothelial and SMC layers. A small amount of an electronlucent material can be seen within the BM, The smooth muscle cells form a continuous single layer and demonstrate small nuclei, few organelles and a poorly differentiated outer border, the latter merging imperceptibly into
Ultrastructure of Renal Arterial Vessels
261
Fig. 4. A large arteriole shows fine deposits of silver in the basement membranes (BM) and cytoplasmic continuity (arrows) between adjacent smooth muscle cells (SMC). Many mitochondria are seen in the SMC. L, lumen. PASI. × 31,000. the interstitium. Figure 7 (PASI) confirms that the convoluted structure is BM. The m e m b r a n e is argyrophilic throughout and almost completely lacks any electron-lucent material. STPPS staining reveals small bands of electrondense elastic tissue within the BM. No electrondense material is found at the outer border of this size vessel. DISCUSSION This ultrastructural study of renal arterial vessels utilizing several staining techniques characterizes three types of small arterial vessels.
T h e y are small artery, large arteriole and small (terminal) arteriole. Each vessel type exhibits three layers: endothelial, basement m e m b r a n e and medial (smooth muscle cell) layer. T h e endothelial cells and layers of smooth muscle cells are of little value in differentiating between the vessels under study. Smooth muscle cells (SMC) appear to differ, however, in that those of the artery are relatively large with comparatively few organelles while those of the large arteriole are generally smaller and apparently more active, with m a n y mitochondria and other organelles. The SMC in the small arterioles are single layered and generally
262
R.D. Bell, J. A. Nordquist, A. K. Mandal and C. L. Rodgers
Fig. 5. A large arteriole reveals electron-dense elastic tissue in the centre of the basement membrane bordered by thick stripes of electron-lucent material (arrows). END, endothelial cells; SMC, smooth muscle cell. STPPS. 5<27,500.
lacking in intracellular organelles. The basement membrane (BM) is characterized by argyrophilia (Walker, 1973), but the BM elastic tissue content (demonstrated by STPPS staining) appears to be the most valuable parameter for differentiating the various types of arterial vessel. Movat and Fernando (1963), have emphasized the value of using the presence or absence of the 'internal elastic lamina' as an important criterion for distinguishing arteries from arterioles. Small arteries are reported to have an internal elastic lamina, while this structure is absent from the small or 'terminal arterioles'. Spiro et al. (1965) suggested that the number of SMC layers could be used to differentiate between large and small arterioles. However, this is not supported by the present study. O n the other hand, the present study has shown that the BM of different sized vessels contains
variable amounts of elastic tissue which decrease in proportion to the size of the vessel. Thus, a small artery contains large amounts of' elastic tissue while a small arteriole has only a small amount of this substance. It is of special interest that the present study has demonstrated elastic tissue in even the smallest of renal arteriolar vessels. These vessels are extremely effective in altering resistance to blood flow and require elastic tissue as well as SMC for graded contraction (Burton, 1966). Acknowledgements--The authors wish to express gratitude to Dr. Marc A. Pfeffer and Mrs. Janice M. Pfeffer, Department of Medicine, Jarvard Medical School (formerly of the Department of Medicine, University of Oklahoma College of Medicine) for providing the kidneys from Wistar rats for this study. The authors are grateful to Ms. Carolyn Clay, secretary, for typing and editing the revised manuscript.
Ultrastructure of Renal Arterial Vessels
263
Fig. 6. A small arteriole exhibits a convoluted basement membrane (BM) with inconspicuous quantities of electron-lucent elastic tissue (arrows). END, endothelial cell; SMC, smooth muscle cell; L, lumen. Free interstitium (I) and tubule (T) are also shown. UA + LC. X 18,000.
REFERENCES Albert, E. N. and Fleischer, E., 1970. A new electrondense stain for elastic tissue. J. Hostochem. Cytochem., 18: 697-708. Burton, A. C., 1966. Walls of the blood vessels and their function. In: Physiology and Biophysics of the Circulation. Yearbook Medical Publishers, Chicago, U.S.A., 72~33. Fernando, N. V. P. and Movat, H. Z., 1964. I. The smallest arterial vessels: Terminal arterioles and metarterioles. Exp. Mol. Path., 3: 1-9. Ham, A. W. and Leeson, T. S., 1961. Histology. Lippincott, Philadelphia.
Heptinstall, R. H., 1954. Renal biopsies in hypertension. Br. HeartaT. 16: 133-141. Leeson, T. S. and Leeson, C. R., 1970. The circulatory system. In: Histology, W. B. Saunders, Philadelphia, U.S.A., 215-233. Moore, D. H. and Ruska, H., 1957. The fine structure of capillaries and small arteries, a7. Biophys. Biochem. Cytol., 3: 457-462. Movat, H. Z. and Fernando, N. V. P., 1963. The fine structure of the terminal vascular bed. I. Small arteries with an internal elastic lamina. Exp. Mol. Path., 2: 549-563.
264
R. 1). Bell..l.A. Nordquist. A. K. Mandal and C. L. Rodgers
Nordquist, J. A., Chrysant, K., and Mandal, A. K., 1975. A modified technique of staining elastic tissue tbr electron microscopic study. In: Proc. 33rd Annual Meeting EII/ISA, Las Vegas, Nevada, Bailey, G. W. (ed.), 626-627. Olson, R. L., Nordquist, J. A. and Everett, M. A., 1967. Lysosomes and the skin. In: Proc. 13th Internat. Congr. Dermatology, Munich, Jadasson, W.
and Schiren, C. (eds.), Springer--Verlag, Berlin, 1056-1060. Spiro, D., Lattes, R. G. and Wiener, J., 1965. l'hc cellular pathology of experimental hypertension. Am. J. Path. 47: 19-49. Walker, F., 1973. The origin, turnover, and removal of glomerular basement membrane. J. Path., 110: 233-244.
Fig. 7. The identity of the basement membrane (BM) in the small arteriole is confirmed by its argyrophilia. Mitochondria and lipid droplets (LI) can be seen in the smooth muscle cell. (SMC). L, lumen. PASI. × 32,000.