the ultramicroscopic structure of a reptilian kidney

The Ultramicroscopic Structure of a Reptilian

EVERETT ANDERSON Department of Zoology, State University of Iowa, Iowa City , Iowa

Since Bowman's (1842) classical studies on the micro-structure and physiology of the kidney, this organ has been the sub- ject of intensive investigation by both cy- tologists and physiologists. Within the past few years the high resolving power of the electron microscope has enabled investigators to study the ultramicroscopic structure of the kidney. The evidence thus obtained has been most valuable in an effort to better understand, not only the ultramicroscopic organization of its cells, i.e., the structure and the spatial relationship of cytoplasmic components, but also the processes involved in renal excretion. Much of the challenging data presented in these studies have been primarily con- cerned with mammals; only a few deal with other forms such as amphibians (Bargmann, et aE., '55; Fawcett, '58) reptiles (Anderson, '58; Anderson and Beams, '59) and birds (Prestage and Beams, '57; Pak Poy and Robertson, '57). Because of this it seems important to study in detail the kidney of a species living in an arid environment, with the hope of adding ultrastructural information that may be help- ful in the understanding of the physiology of such a kidney. We have found that the ultramicroscopic structure of the kidney of the "horned toad," Phyrnosoma, while displaying a cytology similar to that described for other vertebrates, is sufficiently unlike them in detail to warrant presenta- tion of the observations contained in this communication.

MATERIALS AND METHODS

The organism used in this investigation was Phrynosoma curnuturn. They were kept in the laboratory and fed Tenebrio larvae. After anesthetization with Nembu- tal small pieces of kidney tissue were ex- cised for study. For general histological

Kidney'

studies some of the pieces were fixed in Helley's fluid and stained with Heiden- hain's hematoxylin or Masson's trichrome stain; others were fixed in an alcohol- formalin solution and stained with a 0.5% aqueous solution of toluidine blue (Pearse, '54) or with Mayer's mucicarmine for the demonstration of mucus (Mallory, '42). For electron microscopy small pieces were fixed for 30 minutes in a 1% solution of osmium tetroxide buffered at pH 7.5 with acetate veronal buffer. After fixation, the tissue was dehydrated, infiltrated, embedded in methacrylate, and sectioned. Ob- servations were made with Philips Model 100-AZ and RCA EMU-3D electron micro- scopes.

OBSERVATIONS AND DISCUSSION

For an account of the histology of the kidney of Phrynosoma cornutum the reader is referred to a comparative study of the renal unit of vertebrates made by Edwards ('33).

Malpighian corpuscle. The Malpighian corpuscle of Phrynosma is a small, but complex, structure consisting of a glomerulus and Bowman's capsule similar to that found in higher vertebrates. The capsule is lined with a layer of squamous epithelial cells whose flattened cytoplasmic portions can be observed resting on a basement membrane. This portion of the cytoplasm contains mitochondria scattered in a relatively homogeneous cytoplasmic matrix (fig. 1).

The endothelial cells lining the glomerular capillaries are in contact with the basement membrane (figs. 1-3). The nu-

1 Supported by grants (RG 4706 and 5479) from the National Institutes of Health, United States Public Health Service.

2 The author wishes to express his appreciation to the Department of Anatomy, University of Col- orado Medical Center, Denver, Colorado for the use of the Philips Electron Microscope.

205

206 EVERETT ANDERSON

cleus of such cells, surrounded by a thin rim of cytoplasm, projects into the lumen. The extended portions of these cells display intracellular fenestrations (fig. 4) similar to that which has been described for endothelial cells of glomerular capillaries in other types of vertebrates and in the endothelial cells of capillaries associated with glands of internal secretion (Hall, '53; Pease, '55; Rhodin, '55, '58; Ekholm and Sjostrand, '56; Palay, '57; Pak Poy and Robertson, '57; Bennett, et al., '59 and others).

Blood cells, surrounded by what appears to be precipitated plasma, are seen in the lumen of glomerular capillaries. The cytoplasm of red blood cells is dense, but a vacuolar element is sometimes observed with a dense central area, at one pole of the nucleus (figs. 1 and 2). Whether these elements represent stages in the life cycle of an intracellular parasite or are similar to vesicles observed in light microscopy of certain amphibian blood cells is unknown (Dawson, '28).

The glomerular epithelium is contin- uous with the capsular epithelium, the cells of which, exhibit a different geometrical shape as compared with the squamous cells lining the capsule (figs. 1-5). On the basis of their general structure they have been called podocytes (Hall, '53). The podocytes seen in Phrynosoma are similar to those seen in the kidney of other vertebrates and the cytoplasm contains the usual cytoplasmic components such as the Golgi complex, mitochondria, and endoplasmic reticulum (fig. 4). Spherical bodies, in the body of the podocytes, as well as in their pedicular processes, are seen limited by a single-layered membrane which encloses many thin walled vesicles (see insert, fig. 4). These bodies have been described for other cell types (Anderson and van Breemen, '58; Sotelo and Porter, '59). What the significance of such structures is in relation to the function of the podocytes is obscure. In addition to the cytoplasmic structures just mentioned, another cytoplasmic element was observed which is characterized by granules of vari- able densities. These are found in the body and also in the pedicular processes (figs. 4 and 5). This component is unlike the one described by Paiade ('55) but does

resemble the particulate glycogen component depicted by Fawcett and Selby ('58).

The processes of the podocytes, like the endothelial cells of glomerular capillaries, rest on the basement membrane referred to as the lamina densa by Hall ('55). Rhodin ('55) described two areas of lesser density in the basement membrane on either side of the central dense layer. Pease ('55) suggested, in his studies on glomerular structure, that these were ce- ment layers. In a study made on the glomerulus Yamada ('55) reserved the term lamina densa for the broad dense layer and assigned descriptive terms to the layers of lesser density, e.g., lamina T ~ T U externa and lamina ram interna. These seem to be appropriate and will be used in the present study. In the electron micrograph shown in figure 5 the lamina Tarn externa lies adjacent to the pedicular processes and the lamina rara interna next to the plasma membrane of the endothelial cells.

In many electron micrographs, tissue was observed in the glomerulus that was difficult to assign to either the endothelium of glomerular capillaries or to the glomerular epithelium. The basement membrane appears to split and surround this tissue (figs. 1-3). The cells composing this mass do not appear to have an unusual cytology and are thought to be related to the intercapillary tissue or mesangium discussed by Yamada ('55). Not all investigators of the mammalian glomerulus agree as to the existence of intercapillary tissue. Ya- mada ('55) was of the opinion that intercapillary tissue is real in the mouse glomerulus and stated that i t is "-enmeshed within the basement membrane." Hall ('55), however, asserted from his work on a variety of adult mammals, that intercapillary tissue does not occur and Hall and Roth ('56) reached a similar con- clusion after a preliminary study of em- bryonic rat glomerulus. Elias ('56) stated, after his analysis of literature on the mammalian glomerulus, that the "-so-called mesangium does not exist." Instead, the tissue which is not glomerular epithelium nor capillary endothelium, he terms en- denchyma and defines it as "-a contin- uous mass of cells within a basement mem-

REPTILIAN KIDNEY 207

brane; this mass is tunneled by channels through which blood flows but without basement membrane intervening between the neighboring channels.” In a study of the avian glomerulus Pak Poy and Robert- son (’57) demonstrated intercapillary tissue which they referred to as the “inner cell mass.’’

The non-ciliated neck segment of the nephron was not studied because of its infreqeunt appearances in the many sections examined during the course of this study.

Proximal tubule. The proximal segment of the nephron is composed of columnar cells of varying height. At the free surfaces of these cells is a prominent brush border consisting of units which are cylin- drical extensions of the apical cytoplasm in the form of microvilli (fig. 6). At the base of micro-crypts found between microvilli are seen invaginations of the plasma membrane (fig. 7) . Microvilli and invaginations of the plasma membrane have been demonstrated by many electron mi- croscopists to be present, not only in cells of the proximal tubule of the kidney, but also in other cell types (Fawcett, ’58; Pal- ay, ’58; Ladman and Young, ’58 and others). Another feature of the brush border frequently seen is a characteristic blebbing of microvilli (fig. 18). In the lumen of certain preparations, oval-shaped bodies, which are apparently discarded blebs, were observed limited by a thin membrane with an internal structure whose density closely approximates that of the general cytoplasm. A similar blebbing has been demonstrated in the excre- tory organ of Cambarus (Anderson and Beams, ’56) .

From the characteristic blebs that are frequently found at the apical end of these cells and in the lumen of the tubule one may speculate about a possible secretory function of these cells. Cordier (’28), in his histophysiological studies of the reptilian kidney, observed, in Phrynosoma, that the apical portion of cells of the proximal tubule participated in the secretion of uric acid. In Wiggleworth’s (’31) observations on the formation of urine in the insect Rhodnius (which like Phrynosoma, is known to eliminate large quantities of uric acid) it was noted that blebs were

formed at the tips of the units composing the brush border during urine formation. These, however, Wigglesworth dismissed as artefacts. In the proximal tubule of the kidney of Phrynosoma the blebs are not thought to be artefacts, but are considered manifestations of a functional secretory cycle. A plausible but, highly speculative view, is that the material found within the blebs may contain uric acid in solution, and once pinched off water is re- sorbed with a subsequent precipitation of the material as crystalline uric acid.

In the apical part of the cytoplasm are observed many large and small oval-shaped vesicles (figs. 7, 13 and 18). It is thought that many of the vesicular elements seen in this area of the cytoplasm are formed by a process which involves the inpocketing of the plasma membrane. This phenome- non may be comparable to that which was first observed in light microscopy of tissue culture cells by Lewis (’34) and termed by him cell drinking or pinocytosis. It has been observed submicroscopically in both normal and experimental tissues (Palade, ’53; Palay and Karlin, ’56; Ladman and Young, ’58; Clark, ’59 and others).

Nuclei, each with a densely compact nucleolus, are found either in the basal region of the cell or in an intermediate area. In these regions are also seen the Golgi complex, mitochondria and cisternae of the endoplasmic reticulum arranged in parallel array (figs. 6 and 8). Scattered throughout the cytoplasm is a fine particulate component characterized by dense granules as described by Palade (’55).

Mitochondria are scattered throughout the apical, intermediate and basal portions of the cell. In the basal part of the cytoplasm, however, they show no preferred orientation (figs. 6, 8 and 15). This arrangement is unlike that demonstrated in mammalian tubular cells and cells of Mal- pighian tubules of insects, where they are found located in compartments formed by the infolded plasma membrane (Dalton, ’51; Pease, ’55; Beams et al., ’55; Rhodin, ’54, ’58, and others). These organelles are observed to be limited by a distinct membrane and to posses cristae as described by many investigators. The cristae appear to be embedded in a rather fine homogeneous matrix.


In many of the cells studied, a number of large lipid inclusions were encountered. In almost every case, mitochondria were found to display a close anatomical relationship with such inclusions (see insert, fig. 8). The orientation of cristae of the mitochondria associated with the inclusion is similar to those in other areas of the cytoplasm. Many mitochondria, however, were observed whose internal structure consisted of both "normal" cristae and double-membrane lamellae oriented longitudinal to the long axis. Some of these traverse the entire axis (figs. 9-12). A very interesting structure is seen in a mitochondrion shown in figure 12. In the upper left of the organelle, in addition to 8 distinct lamellae, dense areas are seen which appear as nodes alternating with internodal regions composed of parallel elements. Also located in the same mitochondrion are dense areas of varying sizes. Attention is called to the clearly demonstrable external limiting membrane of mitochondria adjacent to lipid inclusions.

Other studies on the ultramicroscopic structure of cells have shown a similar anatomical relationship between mitochondria and lipid inclusions (Lever, '55; Pal- ade and Schidlowsky, '58; Napolitano and Fawcett, '58). It is difficult to state from the present study, what biological significance this relationship might have. Whe- ther the mitochondria are in the process of degenerating or are related in some way to the biosynthesis of lipides is obscure. The author is inclined to accept the latter view.

In the basal portion of the cells, the plasma membrane is thrown into simple and complex infoldings (figs. 14-16). As demonstrated here, the infolded membrane does not divide the basal cytoplasm into compartments. At the base of these cells is sometimes revealed a large mass of dense material (fig. 6) which at higher magnifications is seen to be composed of dense spherical-shaped bodies of varying sizes (fig. 15). These bodies can be observed between folds of the plasma membrane and between adjacent cells (figs. 8, 14-16). Similar bodies, with and without a limiting membrane, are seen in the cytoplasm (figs. 7, 9 and 15). How and

where these are formed and their significance is unknown.

The basal region of the cell rests on a thin, dense, apparently amorphous, layer which is the basement membrane as it appears by electron microscopy (figs. 14 and 15). Subjacent to this layer is an area composed of connective tissue fibrils, which when coupled with the denser layer, may correspond to the basement membrane illustrated in classical histology.

Found in the connective tissue are nerve fibers which display an axoplasm consisting of granules and profiles of small mitochondria (fig. 17). In the upper left and lower center of figure 17 are observed in the axoplasm, profiles of single-layered membrane vesicles which are similar to synaptic vesicles (De Robertis and Ben- nett, ' 55 ) .

Intermediate segment. This segment is composed of cuboidal cells whose apical surfaces are covered with long cilia pro- jecting into the lumen. Scattered in the cytoplasmic ground substance are dense particles. Spherical and sometimes irregular shaped nuclei are seen along with the usual cytoplasmic components (figs. 19- 21).

The cilia are similar in structure to those demonstrated many times by electron microscopy. Non-striated ciliary rootlets ex- tend inwards from the bases of the kinetosomes. In addition to cilia, a few cytoplasmic projections or microvilli are present.

In the basal region of the cells, the plasma membrane which shows no infoldings, rests on a basement membrane which is in turn supported by connective tissue fibrils

The intermediate segment of the reptilian nephron is thought to correspond to the thin segment found in avian and mammalian kidney (cf. Scheer, '48; Huber, '32). It has been suggested by Edwards ('33) and Marshall ('34) that the cilia of the intermediate segment may function as a propulsive mechanism keeping the urine moving as it is received from the proximal tubule.

DistaE tubule. The distal tubule is composed of low columnar cells with nuclei, somewhat irregular in shape, occupying a relatively central position (fig. 2). Scat-

(fig. 19).


tered in the cytoplasmic matrix are many dense granules and mitochondria showing no preferred orientation (figs. 22-24). Many vacuoles of various sizes and limited by a thin membrane are concentrated in the apical cytoplasm.

At the apical end of these cells, the plasma membrane shows few projections in the form of microvilli (figs. 22 and 24). The basal plasma membrane is a relatively smooth-layered entity (figs. 22 and 23) which is unlike that demonstrated for the mammalian distal tubule (Pease, '55; Rho- din, '58). This membrane rests on a basement membrane which is supported by connective tissue fibrils (fig. 22). The plasma membrane is thrown into elaborate folds which interdigitate with similar structures in adjacent cells (figs. 22-26). Such an elaboration of the plasma membrane has been demonstrated for the distal convoluted tubule of Rana pipiens (Fawcett, '58) .

The function of the cells composing the distal tubule of Phrynosoma is at present, not clear. The presence of many vacuoles located in the apical end of the cells may indicate the cells' ability to resorb fluid from the lumen.

Duct portion. While the duct portion is not a part of the nephron, a brief descrip- tion will be included here. The cells composing it are columnar in shape with the nucleus located in the basal cytoplasm (fig. 27). The apical end of the cells pos- sesses few microvilli. The basal plasma membrane shows no infoldings; however, the membrane of adjacent cells are inter- digitated (figs. 27 and 29).

In the supranuclear area of the cell occupying the central position in figure 27, a portion of the smooth-membrane system of the Golgi complex and many tiny vesicles may be observed. In many of the cells large irregular-shaped vacuoles are present some of which appear to have a fine network of material while others show no demonstrable internal structure (figs. 27- 29).

In light microscopy large drops of material occur in the cytoplasm of many of these cells. These stain metachromatically with toluidine blue and give a positive reaction with Mayer's mucicarmine which is thought to be specific for mucous sub-

stances. A similar reaction utilizing mucicarmine was obtained for these cells in Phrynosoma by Cordier ( '28) and Edwards ('33).

Weese ('17) reported that the urine of Phrynosoma is eliminated in a relatively dry form. Observations made in the laboratory have confirmed those of Weese. As stated above, Mayer's mucicarmine demonstrated a mucous substance in many of these cells. From the electron micrographs these cells appear to be in different physiological states; some being morphologically similar to the mucous secreting cells of epithelia described by others (Rhodin and Dalhamn, '56; Palay, '58). It is possible that the cells lining the duct portion elaborate mucous thereby coating and at the same time lubricating the concentrated mass of urine as it passes toward the clo- aca.

SUMMAEY A study of the kidney of Phnposoma

corrzutum has been made with the electron microscope. The Malpighian corpuscle has an architecture similar to that found in higher vertebrates. The cytoplasm of the podocytes, in addition to the usual cytoplasmic components, has granules of various densities.

The cells composing the proximal tubule consist of the usual cytoplasmic components such as Golgi complex, endoplasmic reticulum and mitochondria. In many of the micrographs mitochondria cluster around lipid inclusions. An interesting feature of mitochondria found in such an arrangement is the longitudinal orientation of their internal membranous elements. The basal plasma membrane shows simple and complex infoldings and so is unlike the regular infoldings demonstrated for the proximal tubular cells of mammals. At the bases of these cells lies a mass of material consisting of spherical bodies. These bodies are found between adjacent cells and similar ones are seen in the cytoplasm.

The cells of the intermediate segment have at their surfaces few microvilli and many long cilia. Non-striated ciliary rootlets were observed originating from the bases of the kinetosomes.

In the apical end of cells composing the distal tubule many large and small vacu-


oles are present. The basal plasma membrane shows no infoldings and thus is unlike that demonstrated for the distal tubule of mammals. The lateral plasma membrane shows infoldings which interdigitate with those of adjacent cells.

The duct portion of the kidney is composed of tall columnar cells which appear to be in different physiological states. Many of these cells show large vacuoles and mitochondria are frequently seen between them. In light microscopy, the cytoplasm of many of these cells contain large drops of material which give a positive reaction when stained for mucous with Mayer’s mucicarmine and stains metachromatically with toluidine blue.

LITERATURE CITED Anderson, E., and H. W. Beams 1956 Light and

electron microscopic studies on the cells of the labyrinth in the “green gland” of Cambums sp. Proc. Iowa Acad. Sci., 63: 681-685.

Anderson, E. 1958 A cytological study of the proximal convoluted tubules of the kidney of the “horned toad,” Phrynosoma cornutum. Anat. Rec., 130: 449.

Anderson, E., and H. W. Beams 1958 The ultramicroscopic structure of the renal glomerulus of a lizard. Anat. Rec., 131: 527.

Anderson, E., and V. L. van Breemen 1958 Electron microscopic observations on spinal ganglion cells of Rana pipiens after injection of malononitrile. J. Biophys. Biochem. Cytol.,

Bargmann, W., A. Knoop and Th. H. Schiebler 1955 Histologische, cytochemische und elek- tronenmikroskopische untersuchungen am nephron mit beriicksichtigung der mitochondrien. 2. f. Zellforsch., 42: 386-422.

Beams, H. W., T. N. Tahmisian and R. L. Devine 1955 Electron microscope studies on the cells of the Malpighian tubules of the grasshopper. J. Biophys. Biochem Cytol., I : 197-202.

Bennett, H. S., J. H. Luft and J. C. Hampton 1959 Morphological classification of vertebrate blood capillaries. Am. J. Physiol., 196: 381- 390.

Bowman, W. 1842 On the structure and use of the Malpighian bodies of the kidney, with observations on the circulation through that gland. Phil. Trans. Roy. SOC., pt. I : 57-80.

Clark, S. L. 1959 The ingestion of proteins and colloidal materials by columnar absorptive cells of the small intestine in suckling rats and mice. J. Biophys. Biochem. Cytol., 5: 41-50.

Cordier, R. 1928 Etudes histophysiologiques sur le tube urinaire de reptiles. Arch. de Biol., 38:

Dalton, A. J. 1951 Structural details of some of the epithelial cell types in the kidney of the mouse as revealed by the electron microscope. J. Nat. Cancer Inst., 11: 1163-1185.

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De Robertis, E. D. P., and H. S. Bennett 1955 Some featurse of the submicroscopic morphology of synapses in frog and earthworm. J. Bio- phys. Biochem. Cytol., I: 47-58.

Dawson, A. B. 1928 The “segregation apparatus” of the amphibian erythrocyte and its possible relation to the Golgi apparatus. Anat. Rec., 39: 137-154.

Edwards, J. G. 1933 The renal unit in the kidney of vertebrates. Am. J. Anat., 53: 55-87.

Ekholm, R. and F. S. Sjostrand 1956 The uI- trastructure of the thyroid gland of the mouse. Electron Microscopy: Proc. of the Stockholm Conf., pp. 171-173 (F. S. Sjostrand and J. Rhodin, eds.) Almquist and Wiksel, Stockholm and Academic Press, New York.

Elias, H. 1956 The renal glomerulus by light and electron microscopy. Res. Serv. Med., 46:

Fawcett, D. W., and C. C. Selby 1958 Observa- tions on the fine structure of the turtle atrium. J. Biophys. Biochem. CytoI., 4: 63-72,

Fawcett, D. W. 1958 Structural specializations of the cell surface In: Frontiers in Cytology, (S. L. Palay, ed.), Yale Univ. Press, New Haven.

Hall, B. V. 1953 Studies on normal glomerular structure by electron microscopy. Proc. V An- nual Conf. on the Nephrotic Syndrome, pp, 1- 39, New York. - 1955 Further studies on the normal

structure of the renal glomerulus. Proc. VI An- nual Conf. on the Nephrotic Syndrome, pp. 1-40, New York.

Hall, B. V., and L. E. Roth 1956 Preliminary studies on the development and differentiation of cells and structures of the renal corpuscle. Electron Microscopy: Proc. of the Stockholm Conf., pp. 176-179 (F. S. Sjostrand and J. Rhodin, eds. ) Almquist and Wiksel, Stockholm and Academic Press, New York.

Huber, G. C. 1932 Renal tubules In: Special Cytology (E. V. Cowdry, ed.) Paul B. Hoeber, Inc. New York.

Ladman, A. J., and W. C. Young 1958 An electron microscopic study of the ductuli efferentes and rete testis of the guinea pig. J. Biophys. Biochem. Cytol., 4: 219-226.

Lever, J D. 1957 The fine structure of brown adipo-c tissue in the rat with observations on the cytdogical changes following starvation and adrenalectomy. Anat. Rec., 128: 361-378.

Lewis, W. 1931 Pinocytosis. Bull. Johns Hop- kins Hos.nita1, 49: 17-28.

Marshall, E. K., Jr. 1934 The comparative physiology of the kidney in relation to theories of renal secretion. Physiol. Revs., 14: 133-159.

Mallory, F. B. 1942 Pathological Techniques. W. B. Saunders Co., Philadelphia.

Napolitano, L., and D. Fawcett 1958 The fine structure of brown adipose tissue in the new- born mouse and rat. J. Biophys. Biochem. Cy-

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1955 A small particulate component of the cytoplasm. J. Biophys. Biochem. Cytol., 1: 59-68.

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Palay, S. L., and L. Karlin 1956 Absorption of fat by jejunal epithelium in the rat. Anat. Rec., 124: 343.

Palay, S. L. 1957 The fine structure of the neurohypophysis In: Progress In Neurobiology: I1 Ultrastructure and Cellular Chemistry of Neural Tissue (H. Waelsch, ed.), Paul B. Hoeber, Inc., New York.

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the electron microscope. Proc. Iowa Acad. Sci., 64: 670-679.

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1954 Correlation of ultrastructural organization and function in normal and experimental changed proximal convoluted cells of the mouse kidney. Karolinska Institutet, Stock- holm.

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5 72-574.

PLATE 1

EXPLANATION O F FIGURE

1 A low power electron micrograph illustrating the major parts of a Malpighian corpuscle. The glomerular capillaries are lined with endothelial cells (ED) which are observed resting on a basement membrane (EM). Red blood cells (RBC) with a relatively dense nucleus ( N ) and dense cytoplasm occupy the lumen of capillaries. In some of the red blood cells are seen vacuolar elements (BV) many of which have a central dense area. A macrophage is observed in the lower right of the figure. Intercapillary tissue (IC) is seen in the approximate center of the micrograph. The processes of podocytes (PC) rest on the basement membrane (EM). Bowman’s capsule is lined by squamous epithelial cells and the cytoplasm of one is seen at C. Bowman’s space (BS) and a part of a renal tubuIe (T) are aIso demonstrated. x 1200.

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PLATE 1

213

PLATE 2

EXPLANATION O F FIGURES

2 and 3 Sections showing portions of glomerular capillaries lined with endothelial cells (ED), intercapillary tissue (IC) which appears to be surrounded by the basement membrane (BM, fig. 2) and podocytes ( P C ) . Blood cells (RBC) are observed in the lumen of the capillary in figure 3 showing two vacuolar elements ( S V ) at one pole of the nucleus ( N ) . Figure 2, X 4600; figure 3, X 4600.

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REPTILIAN KlDNEY Everett Anderson

PLATE 2

215

PLATE 3

EXPLANATION OF FIGURES

4 and 5 Enlarged areas showing portions of epithelial and endothelial cells of glomerular capillaries. In the upper left of figure 4 is a part of the nucleus of a podocyte. Scattered in the cytoplasm may be seen the Golgi complex (GC) , mitochondria (M) , endoplasmic reticulum (ER) and granules (G). In the body, as well as in the pedicular processes (sce insert, fig, 4 ) are seen spherical bodies limited by a thin membrane which cn- closes thin walled vesicles. The capillaries are lined with endothelial cells (ED) the cytoplasm of which displays fenestrations (PED, fig. 4). The basement membrane (fig. 5) is composed of the lamina densa (LD), lamina rara externa (LRE) and lamina ram interna (LRI). A small portion of a macrophage is observed in the lower right of figure 4. Figure 4, x 30,000; figure 5, X 40,000.

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PLATE 3

217

PLATE 4

EXPLANATION OF FlGURES

6 and 7 Sections showing cells from the proximal tubule. At the surface of these cells is the brush border composed of microvilli (MV). Be- tween the microvilli, as illustrated in figure 7, are observed invaginations of the plasma membrane (IV). The cytoplasm contains mitochondria (M), endoplasmic reticulum (ER) , nucleus ( N ) with its dense nucleolus (NCL), spherical bodies (DG) and similar bodies limited by a thin membrane ( D G , fig. 7 ) as well as vacuoles (V). At the base of the cells located in figure 6 is seen a mass of dense material (MDG). At X in figure 7 is an unidentified body. Figure 6, x 3000; figure 7, x 40,000.

218


PLATE 4

219

PLATE 5

EXPLANATION OB FIGURE

8 Section showing the intermediate cytoplasmic area of two adjacent cells of the proximal tubule. At the top left of the figure is seen a part of the nucleus. The cytoplasmic organelles such as the Golgi complex ( G C ) , endoplasmic reticulum (ERj, mitochondria ( M ) as well as a lipide inclusion (LPj are illustrated. Between the plasma membrane (CM) of adjacent cells are dense bodies (DG). The insert shows a large dcnse lipid inclusion with mitochondria ( M j closely associated with its surface. x 36,000.

220


PLATE 5

22 1

PLATE 6


9-12 Small fields of the cytoplasm of proximal tubular cells showing the close relationship of mitochondria with lipid inclusions (LP). The internal structure of mitochondria is observed to be composed of cristae and longitudinally oriented lamellae. In figure 10 one lamella (E) completely travcrses the long axis of the organelle while two others are incomplete ( S ) . In figure 12, in the upper portion of the mitochondrion, dense areas alternate with parallel elements. Dense spherical bodies (DG2, fig. 9) limited by a thin membrane are also illustrated. Figures 9-11, X 36,000; figure 12, 45,000.

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PLATE 6

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PLATE 7


13 A small area of the apical end of cells of the proximal tubule. The microvilli (MV), a desmosome (D), vesicular structures ( V ) and an unidentified body at Y are illustrated. x 40,000.

14 A small portion of the basal cytoplasmic area of a cell from the proximal tubule. In this figure is demonstrated dense bodies (DG) between two folds of the plasma membrane (CM) which is observed resting 011 a basement membrane (BM) supported by connective tissue fibrils (F). X 40,000.

224


PLATE 7

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15 Small fields of the basal cytoplasmic regions of two adjacent cells of the proximal tubule. At the upper left side of the micrograph is observed the complex infolded plasma membrane (CM). The plasma membrane rests on a basement membrane (BM) which is supported by connective tissue fibrils (F). Between the folds are dense bodies (DG) and similar bodies are seen in the cytoplasm (DG2). Mitochondria ( M ) , spherical bodies (SB) and an unidentified body (L) are also illustrated. X 27,000.

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16 A small field of the basal cytoplasmic region of a cell of the proximal tubule showing the complex infolded plasma membrane (CM). X 40,000.

17 Cross-section of axons located in the region of the proximal tubule. In the axoplasm of the upper left and lower center axons are seen thin walled vesicles (SV). Mitochondria are labeled M and connective tissue CT. X 40,000.

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EXPLANATION OF FIGURE

18 Section of the apical portions of cells of the proximal tubule showing microvilli (MV), blebbing of microvilli (B) , desmosomes ( D ) , vacuoles ( V ) and mitochondria (M). x 20,000.

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19-21 A cross-section of the intermediate segment showing cross- sections of cilia in the lumen ( C ) . Nuclei are labeled N, mitochondria M and connective tissue F (fig. 19). At higher magnifications the details of cilia ( C ) and microvilli (MV) at the apical cnd of the cells are clearly seen (fig. 20-21). Originating from the bases of the kinetosomes ( K ) are non-striated ciliary rootlets (CR, fig. 21) and cross-sections of ciliary rootlets (CR) are seen in figure 20. A desmosome is labeled D. Figure 19, X 5000; figure 20, x 40,000; figure 21, x 30,000.

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22-23 Tangential sections of cells from the distal tubule. The apical plasma membrane is seen to possess few microvilli (MV) and the lateral one is thrown into elaborate infoldings (CM). The cells rest on a basement membrane which is supported by connective tissue fibrils (F) . Mito- chondria are labeled M and nuclei N. On the right of figure 22 is a portion of the proximal tubule. Figure 23, x 10,000; figure 24, x 30,000.

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24-26 Tangential sections illustrating small fields of cells of the distal tubule. In the apical cytoplasm are many large and small vacuoles (V, fig. 24). The nuclei are labeled N, mitochondria M and microvilli MV. Note the elaborate infolding of the lateral plasma membrane (CM) in all figures. All figures X 40,000.

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REPTILIAN KIDNEY Everett Anderson PLATE 13

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27 A tangential section of cells of the duct portion of the kidney. The Golgi complex is labeled GC, tiny vesicles TV, mitochondria M, nuclei N, vacuoles V, microvilli M V and connective tissue F . x 8500.

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28-29 High power electron micrographs of apical areas of cells composing the duct portion. Mitochondria are labeled M, vacuoles V, desmosome D, microvilli MV and the infolded lateral plasma membrane CM x 40,000.

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the ultramicroscopic structure of a reptilian kidney

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