Ac la anal. 97: 205-212 (1977)
Ultrastructure of the parathyroid glands in the chicks An Soo Chan Department of Pathology and the Research Institute, Hospital for Sick Children and University of Toronto, Toronto, Ont., Canada
Key words. Parathyroid gland • Chicks • Secretory granules • Ultrastructure
Introduction The ultrastruclure of the avian parathyroid glands has been reported in the chick embryos [Narhain, 1972] and in the laying hens [Nevalainen. 1969; Gould and Hodges, 1971 ; Stoeckel and Porte, 1973]. Apart for a few brief accounts of the parathyroid glands of the immature chicks in the reports of the parathyroid glands of the hens [Gould and Hodges, 1971: Stoeckel and Porte, 1973], there has not been any attempt at
the ultrastruclural study of this gland in the young chicks. In the chicks, the homeostatic regulation of serum calcium is uncomplicated by the influence of large amounts of estrogen. The purpose of the present investigation was to evaluate the ultrastruclural characteristics of the para thyroid glands in the young chicks. The observations recorded here will provide a morphological basis for subsequent studies on the physiological and patholog ical alterations of the parathyroid glands in the chicks.
Downloaded by: Karolinska Institutet, University Library 130.237.122.245 - 2/4/2019 12:49:27 PM
Abstract. The ultrastructure of the parathyroid glands in 4-week-old white leghorn chicks has been examined. The gland consists of chief cells arranged in diffuse cords or solid masses. The chief cells vary in electron density. The rough-surfaced endoplasmic reticulum is invariably moderately to well developed and consists of cistcrnae arranged in well-ordered patterns or distributed randomly. The Golgi complex consists of cisternae arranged in concentric layers, smooth-surfaced and coated vesicles. Cisternae of the Golgi complex arranged in circular and tortuous profiles are also observed. The chief cells contain occasional membrane-limited secre tory granules 150-350 nm in diameter and with contents which vary in electron density. Secre tory granules are distributed randomly in the cytoplasm and along with the plasma membrane. Images of fusion of coated vesicles with the plasma membrane are sometimes observed. The cytoplasm also contains round- to rod-shaped mitochondria, lysosome-like structures and oc casional lipid bodies. Dark cells with electron-dense cytoplasm and containing organelles in close proximity arc also observed. Morphological evidence of synthetic and secretory activities in the chief cells suggests active parathyroid function in the rapidly growing chicks.
Materials and methods 30 4-weck-old white leghorn chicks were used. Tissues were fixed either by immersion in 6.25%glutaraldehyde in 0.2 M cacodylate buffer or by perfusion of the whole animal with 2% glularaldehyde in 0.2 M cacodylate buffer for 10 min. Tissues were further fixed in 6.25% glularaldehyde in 0.2 M cacodylate buffer, pH 7.4, for 2 h and postfixed in 1% osmium tetroxide in Veronal acetate buffer, pH 7.4, for 1.5 h. Tissues were dehydrated in a graded scries of ethanol solutions and embedded in Epon [Ltifl. 1961). Thin sections were cut on the LKB Ultrotome III and Porter-Blum micro tomes, stained with uranyl acetate [ Watson, 1958] and lead citrate [Reynolds, 1963). Sections were examined in the Philips EM 300 electron microscope at 60 kV.
Results The parenchyma of the parathyroid glands in the chicks consisted of chief cells arranged in diffuse cords or solid masses (fig. I). Each group of the chief cells was surrounded by a basement membrane and separated by ca pillaries and fibroblasts. The chief cells were polygonal, oval or elongated. Plasma mem branes of adjacent cells were relatively straight and were folded and interdigitated in some places. The intercellular spaces were narrow and rather uniform and occasional enlarge ments were observed. Opposing plasma mem branes were interconnected by desmosomes (fig. 5). The nucleus was slightly oval or round in outline. The nucleoplasm consisted of finely granular electron-dense material, ex cept peripherally where the chromatin was concentrated along the nuclear membrane. The nucleus usually contained one or more nucleoli. The cytoplasm of the chief cells varied in electron density (fig. 4, 6) and contained vary ing numbers of free ribosomes. The endo plasmic reticulum consisted mainly of the rough-surfaced type. The degree of develop
ment of the endoplasmic reticulum varied among the individual chief cells. In some cells, the cisternae of the endoplasmic reticulum were arranged in parallel arrays (fig.3). In others, the cisternae assumed the forms of membranous sacs and were distributed ran domly throughout the cytoplasm (fig.6). The lumen of the cisternae usually contained some fiocculent material (fig. 3,5). There was a similar variant in the develop ment of the Golgi complex in the chief cells. Cells with well-developed endoplasmic retic ulum usually contained one or more Golgi complexes. In such cases, the Golgi complex consisted of 3-4 curved cisternae arranged in concentric layers. Clusters of smooth-sur faced vesicles, vacuoles and coated vesicles were present in the Golgi region (fig. 3). In some chief cells, the cisternae of the Golgi complex were thickened and arranged in circular and tortuous profiles (fig.2). How ever, in other chief cells, the Golgi complex was poorly developed or absent. The cytoplasm of the chief cells contained occasional secretory granules (fig.4). They varied from round to rod-shaped and measur ed from 150 to 350 nm in diameter. Individual secretory granules were bounded by a smooth limiting membrane and contained a finely granular matrix which varied from moderately to markedly electron-dense (fig.4). Secretory granules were distributed randomly through out the cytoplasm. However, in some cells, the secretory granules w'ere lined close to the plasma membrane. Occasionally, masses of electron-dense material were observed in the enlarged portions of the intercellular spaces (fig-4). Coated vesicles were found in the cyto plasm and especially in the Golgi region. In addition, coated vesicles which were fused with the plasma membrane were observed
Downloaded by: Karolinska Institutet, University Library 130.237.122.245 - 2/4/2019 12:49:27 PM
Chan
206
Fig. 1. Low magnification of the parathyroid gland in the chick. Chief cells are arranged in solid mass and enclosed by the basement membrane (Bm). Plasma
207
membranes are relatively straight and folded in some places. Occasional lipids (L) and secretory granules (Sg) are present, x 7,580.
Downloaded by: Karolinska Institutet, University Library 130.237.122.245 - 2/4/2019 12:49:27 PM
Ultrastructure of the chick parathyroid glands
Fig. 2. Golgi complexes (G) of chief cells showing the arrangement of cisternae in circular and tortuous profiles, x 8,770. Fig. 3. Golgi region of a chief cell. Cisternae are some fiocculent material. Mitochondria (m) contain
Chan
arranged in concentric layers. Smooth-surfaced vesicles (Sv), coated vesicles (Cv) and vacuoles (V) are present. Cisternae of the rough-surfaced endoplasmic reticulum (Rcr) are arranged in parallel array and contain dense and homogeneous matrix and distinct cristac. x 24.370.
Downloaded by: Karolinska Institutet, University Library 130.237.122.245 - 2/4/2019 12:49:27 PM
208
Fig. 4. Chief cells vary in electron density and contain secretory granules (Sg), some of which are lined near the plasma membrane. Masses of electrondense material are present in the intercellular space (arrow). Mitochondria (m) contain dense and homo geneous matrix and distinct cristae. Rough-surfaced endoplasmic reticulum (Rer), Golgi complex (G), lipid bodics(L) and free ribosomes(r) arc present, x 11,870.
209
Fig. 5. Peripheral portion of chief cells showing the fusion of the coated vesicles with the plasma membrane (arrows). Cisternae of the rough-surfaced endoplasmic reticulum (Rer) contain flocculent ma terial. A desmosome (D) between the chief cells is present, x 18,810.
Downloaded by: Karolinska Institutet, University Library 130.237.122.245 - 2/4/2019 12:49:27 PM
Ultrastructure of the chick parathyroid glands
Fig. 6. Chief cells vary in electron density. Cisternac of the rough-surfaced endoplasmic reticulum (Rer) are
Chan
and contain mitochondria (m) and free ribosomes (r) in close proximity, x 7,580.
Downloaded by: Karolinska Institutet, University Library 130.237.122.245 - 2/4/2019 12:49:27 PM
210
(fig. 5). Mitochondria were present throughout the cytoplasm in moderate numbers. In gene ral, they varied from round to rod-shaped. The mitochondrial matrix was dense and homo geneous and the cristae were distinct (fig. 3,4). Occasionally, lipid bodies of variable size and density, lysosome-like structures, multivesicular bodies and filaments were observed in the cytoplasm. Dark cells were also observed in the para thyroid glands in the chicks. The cells were relatively electron-dense due to the close proximity of the organelles, numerous ribo somes and the overall density of the back ground cytoplasmic matrix (fig. 6). The nucleus was ovoid, elongated or somewhat irregular in shape and usually contained one or more nucleoli.
Discussion The general ultrastructural organization of the parathyroid glands in the chicks is similar to that described in the chick embryos [Narbaitz, 1972], in the young adult chickens [Youshak and Capen, 1970],and in the laying hens [Nevalainen, 1969: Gould and Hodges, 1971: Fujii and Isono, 1972; Stoeckel and Porte, 1973]. In the chicks, the parathyroid glands consist of chief cells in various stages of functional activity. However, presence of prominent organelles concerned with meta bolic and synthetic activities in many chief cells suggests active parathyroid function in the rapidly growing chicks. In the chicks, the chief cells are characteriz ed by the presence of relatively few secretory granules. Few secretory granules have also been noted in the chief cells of the chick embryos [Narbaitz, 1972], of the young adult chickens [ Youshak and Capen, 1970] and of
211
the laying hens [Nevalainen, 1969; Gould and Hodges, 1971; Stoeckel and Porte, 1973]. Nevertheless, numerous homogeneously dense bodies thought to be secretory granules have been reported in the chief cells of the laying hens [Fuji! and Isono, 1972]. It is evident that more information is needed to clarify the number and nature of the secretory granules in the chief cells of the laying hens. Cherian and Cipera [1968] have suggested that the rapid decrease of serum calcium after parathyroidectomy in the chicks is related to the short life of the endogenous parathyroid hormone. Presumably, the paucity of the secretory granules in the avian chief cells may be related to the need for the secretory pro duct to be secreted continuously to maintain normal serum calcium levels. The mechanism of release of the secretory product in the avian chief cells is not known. Nevalainen [1969] has suggested that most of the secretory product in the chief cells of the laying hens is transported and discharged as prosecretory granules into the extracellular space. Likewise, in the chief cells of the chick ens, immature prosecretory granules have also been described to represent final secre tory product and are discharged into the extracellular space [ Youshak and Capen, 1970]. In the present study, images of fusion of prosecretory granules with the plasma mem brane are not observed. However, the close association of the secretory granules with the plasma membrane suggests that the limiting membrane of the secretory granule may attach to the plasma membrane or fuse with it and release the secretory product into the extra cellular space in a manner similar to that de scribed in the mouse chief cells [Stoeckel and Porte, 1966]. The role of the coated vesicles in the chief cells of the avian parathyroid glands remains
Downloaded by: Karolinska Institutet, University Library 130.237.122.245 - 2/4/2019 12:49:27 PM
Ultrastructure of the chick parathyroid glands
Chan
212
References Bowers, B.: Coated vesicles in the pericardial cells of the aphid (Myzus persicae Sulz). Protoplasma 59: 351-367(1964). Cherian, A.G. and Cipera, J.D .: Effects of para thyroidectomy and of administration of para thormone on serum calcium in immature chicks. Poultry Sci. 47: 76-82 (1968). Douglas, W.W.: Nagasawa, J., and Schultz, R.A.: Coated microvesicles in neurosecretory terminals of posterior pituitary glands shed their coats to become smooth ‘synaptic' vesicles. Nature, Lond. 232: 340-341 (1971). Fujii, H. and lsono, H.: Ultraslructural observations on the parathyroid glands of the hen (Gallus domesticus) Arehvm histol. jap. 34: 155-165 (1972). Gould, R.P. and Hodges, R.D.: Studies on the fine structure of the avian parathyroid glands and ultimobranchial bodies, in Heller and Lederis Sub-
cellular organization and function in endocrine tissues, pp.567-604 (Cambridge Unis
Ultrastructure of the parathyroid glands in the chicks An Soo Chan Department of Pathology and the Research Institute, Hospital for Sick Children and University of Toronto, Toronto, Ont., Canada
Key words. Parathyroid gland • Chicks • Secretory granules • Ultrastructure
Introduction The ultrastruclure of the avian parathyroid glands has been reported in the chick embryos [Narhain, 1972] and in the laying hens [Nevalainen. 1969; Gould and Hodges, 1971 ; Stoeckel and Porte, 1973]. Apart for a few brief accounts of the parathyroid glands of the immature chicks in the reports of the parathyroid glands of the hens [Gould and Hodges, 1971: Stoeckel and Porte, 1973], there has not been any attempt at
the ultrastruclural study of this gland in the young chicks. In the chicks, the homeostatic regulation of serum calcium is uncomplicated by the influence of large amounts of estrogen. The purpose of the present investigation was to evaluate the ultrastruclural characteristics of the para thyroid glands in the young chicks. The observations recorded here will provide a morphological basis for subsequent studies on the physiological and patholog ical alterations of the parathyroid glands in the chicks.
Downloaded by: Karolinska Institutet, University Library 130.237.122.245 - 2/4/2019 12:49:27 PM
Abstract. The ultrastructure of the parathyroid glands in 4-week-old white leghorn chicks has been examined. The gland consists of chief cells arranged in diffuse cords or solid masses. The chief cells vary in electron density. The rough-surfaced endoplasmic reticulum is invariably moderately to well developed and consists of cistcrnae arranged in well-ordered patterns or distributed randomly. The Golgi complex consists of cisternae arranged in concentric layers, smooth-surfaced and coated vesicles. Cisternae of the Golgi complex arranged in circular and tortuous profiles are also observed. The chief cells contain occasional membrane-limited secre tory granules 150-350 nm in diameter and with contents which vary in electron density. Secre tory granules are distributed randomly in the cytoplasm and along with the plasma membrane. Images of fusion of coated vesicles with the plasma membrane are sometimes observed. The cytoplasm also contains round- to rod-shaped mitochondria, lysosome-like structures and oc casional lipid bodies. Dark cells with electron-dense cytoplasm and containing organelles in close proximity arc also observed. Morphological evidence of synthetic and secretory activities in the chief cells suggests active parathyroid function in the rapidly growing chicks.
Materials and methods 30 4-weck-old white leghorn chicks were used. Tissues were fixed either by immersion in 6.25%glutaraldehyde in 0.2 M cacodylate buffer or by perfusion of the whole animal with 2% glularaldehyde in 0.2 M cacodylate buffer for 10 min. Tissues were further fixed in 6.25% glularaldehyde in 0.2 M cacodylate buffer, pH 7.4, for 2 h and postfixed in 1% osmium tetroxide in Veronal acetate buffer, pH 7.4, for 1.5 h. Tissues were dehydrated in a graded scries of ethanol solutions and embedded in Epon [Ltifl. 1961). Thin sections were cut on the LKB Ultrotome III and Porter-Blum micro tomes, stained with uranyl acetate [ Watson, 1958] and lead citrate [Reynolds, 1963). Sections were examined in the Philips EM 300 electron microscope at 60 kV.
Results The parenchyma of the parathyroid glands in the chicks consisted of chief cells arranged in diffuse cords or solid masses (fig. I). Each group of the chief cells was surrounded by a basement membrane and separated by ca pillaries and fibroblasts. The chief cells were polygonal, oval or elongated. Plasma mem branes of adjacent cells were relatively straight and were folded and interdigitated in some places. The intercellular spaces were narrow and rather uniform and occasional enlarge ments were observed. Opposing plasma mem branes were interconnected by desmosomes (fig. 5). The nucleus was slightly oval or round in outline. The nucleoplasm consisted of finely granular electron-dense material, ex cept peripherally where the chromatin was concentrated along the nuclear membrane. The nucleus usually contained one or more nucleoli. The cytoplasm of the chief cells varied in electron density (fig. 4, 6) and contained vary ing numbers of free ribosomes. The endo plasmic reticulum consisted mainly of the rough-surfaced type. The degree of develop
ment of the endoplasmic reticulum varied among the individual chief cells. In some cells, the cisternae of the endoplasmic reticulum were arranged in parallel arrays (fig.3). In others, the cisternae assumed the forms of membranous sacs and were distributed ran domly throughout the cytoplasm (fig.6). The lumen of the cisternae usually contained some fiocculent material (fig. 3,5). There was a similar variant in the develop ment of the Golgi complex in the chief cells. Cells with well-developed endoplasmic retic ulum usually contained one or more Golgi complexes. In such cases, the Golgi complex consisted of 3-4 curved cisternae arranged in concentric layers. Clusters of smooth-sur faced vesicles, vacuoles and coated vesicles were present in the Golgi region (fig. 3). In some chief cells, the cisternae of the Golgi complex were thickened and arranged in circular and tortuous profiles (fig.2). How ever, in other chief cells, the Golgi complex was poorly developed or absent. The cytoplasm of the chief cells contained occasional secretory granules (fig.4). They varied from round to rod-shaped and measur ed from 150 to 350 nm in diameter. Individual secretory granules were bounded by a smooth limiting membrane and contained a finely granular matrix which varied from moderately to markedly electron-dense (fig.4). Secretory granules were distributed randomly through out the cytoplasm. However, in some cells, the secretory granules w'ere lined close to the plasma membrane. Occasionally, masses of electron-dense material were observed in the enlarged portions of the intercellular spaces (fig-4). Coated vesicles were found in the cyto plasm and especially in the Golgi region. In addition, coated vesicles which were fused with the plasma membrane were observed
Downloaded by: Karolinska Institutet, University Library 130.237.122.245 - 2/4/2019 12:49:27 PM
Chan
206
Fig. 1. Low magnification of the parathyroid gland in the chick. Chief cells are arranged in solid mass and enclosed by the basement membrane (Bm). Plasma
207
membranes are relatively straight and folded in some places. Occasional lipids (L) and secretory granules (Sg) are present, x 7,580.
Downloaded by: Karolinska Institutet, University Library 130.237.122.245 - 2/4/2019 12:49:27 PM
Ultrastructure of the chick parathyroid glands
Fig. 2. Golgi complexes (G) of chief cells showing the arrangement of cisternae in circular and tortuous profiles, x 8,770. Fig. 3. Golgi region of a chief cell. Cisternae are some fiocculent material. Mitochondria (m) contain
Chan
arranged in concentric layers. Smooth-surfaced vesicles (Sv), coated vesicles (Cv) and vacuoles (V) are present. Cisternae of the rough-surfaced endoplasmic reticulum (Rcr) are arranged in parallel array and contain dense and homogeneous matrix and distinct cristac. x 24.370.
Downloaded by: Karolinska Institutet, University Library 130.237.122.245 - 2/4/2019 12:49:27 PM
208
Fig. 4. Chief cells vary in electron density and contain secretory granules (Sg), some of which are lined near the plasma membrane. Masses of electrondense material are present in the intercellular space (arrow). Mitochondria (m) contain dense and homo geneous matrix and distinct cristae. Rough-surfaced endoplasmic reticulum (Rer), Golgi complex (G), lipid bodics(L) and free ribosomes(r) arc present, x 11,870.
209
Fig. 5. Peripheral portion of chief cells showing the fusion of the coated vesicles with the plasma membrane (arrows). Cisternae of the rough-surfaced endoplasmic reticulum (Rer) contain flocculent ma terial. A desmosome (D) between the chief cells is present, x 18,810.
Downloaded by: Karolinska Institutet, University Library 130.237.122.245 - 2/4/2019 12:49:27 PM
Ultrastructure of the chick parathyroid glands
Fig. 6. Chief cells vary in electron density. Cisternac of the rough-surfaced endoplasmic reticulum (Rer) are
Chan
and contain mitochondria (m) and free ribosomes (r) in close proximity, x 7,580.
Downloaded by: Karolinska Institutet, University Library 130.237.122.245 - 2/4/2019 12:49:27 PM
210
(fig. 5). Mitochondria were present throughout the cytoplasm in moderate numbers. In gene ral, they varied from round to rod-shaped. The mitochondrial matrix was dense and homo geneous and the cristae were distinct (fig. 3,4). Occasionally, lipid bodies of variable size and density, lysosome-like structures, multivesicular bodies and filaments were observed in the cytoplasm. Dark cells were also observed in the para thyroid glands in the chicks. The cells were relatively electron-dense due to the close proximity of the organelles, numerous ribo somes and the overall density of the back ground cytoplasmic matrix (fig. 6). The nucleus was ovoid, elongated or somewhat irregular in shape and usually contained one or more nucleoli.
Discussion The general ultrastructural organization of the parathyroid glands in the chicks is similar to that described in the chick embryos [Narbaitz, 1972], in the young adult chickens [Youshak and Capen, 1970],and in the laying hens [Nevalainen, 1969: Gould and Hodges, 1971: Fujii and Isono, 1972; Stoeckel and Porte, 1973]. In the chicks, the parathyroid glands consist of chief cells in various stages of functional activity. However, presence of prominent organelles concerned with meta bolic and synthetic activities in many chief cells suggests active parathyroid function in the rapidly growing chicks. In the chicks, the chief cells are characteriz ed by the presence of relatively few secretory granules. Few secretory granules have also been noted in the chief cells of the chick embryos [Narbaitz, 1972], of the young adult chickens [ Youshak and Capen, 1970] and of
211
the laying hens [Nevalainen, 1969; Gould and Hodges, 1971; Stoeckel and Porte, 1973]. Nevertheless, numerous homogeneously dense bodies thought to be secretory granules have been reported in the chief cells of the laying hens [Fuji! and Isono, 1972]. It is evident that more information is needed to clarify the number and nature of the secretory granules in the chief cells of the laying hens. Cherian and Cipera [1968] have suggested that the rapid decrease of serum calcium after parathyroidectomy in the chicks is related to the short life of the endogenous parathyroid hormone. Presumably, the paucity of the secretory granules in the avian chief cells may be related to the need for the secretory pro duct to be secreted continuously to maintain normal serum calcium levels. The mechanism of release of the secretory product in the avian chief cells is not known. Nevalainen [1969] has suggested that most of the secretory product in the chief cells of the laying hens is transported and discharged as prosecretory granules into the extracellular space. Likewise, in the chief cells of the chick ens, immature prosecretory granules have also been described to represent final secre tory product and are discharged into the extracellular space [ Youshak and Capen, 1970]. In the present study, images of fusion of prosecretory granules with the plasma mem brane are not observed. However, the close association of the secretory granules with the plasma membrane suggests that the limiting membrane of the secretory granule may attach to the plasma membrane or fuse with it and release the secretory product into the extra cellular space in a manner similar to that de scribed in the mouse chief cells [Stoeckel and Porte, 1966]. The role of the coated vesicles in the chief cells of the avian parathyroid glands remains
Downloaded by: Karolinska Institutet, University Library 130.237.122.245 - 2/4/2019 12:49:27 PM
Ultrastructure of the chick parathyroid glands
Chan
212
References Bowers, B.: Coated vesicles in the pericardial cells of the aphid (Myzus persicae Sulz). Protoplasma 59: 351-367(1964). Cherian, A.G. and Cipera, J.D .: Effects of para thyroidectomy and of administration of para thormone on serum calcium in immature chicks. Poultry Sci. 47: 76-82 (1968). Douglas, W.W.: Nagasawa, J., and Schultz, R.A.: Coated microvesicles in neurosecretory terminals of posterior pituitary glands shed their coats to become smooth ‘synaptic' vesicles. Nature, Lond. 232: 340-341 (1971). Fujii, H. and lsono, H.: Ultraslructural observations on the parathyroid glands of the hen (Gallus domesticus) Arehvm histol. jap. 34: 155-165 (1972). Gould, R.P. and Hodges, R.D.: Studies on the fine structure of the avian parathyroid glands and ultimobranchial bodies, in Heller and Lederis Sub-
cellular organization and function in endocrine tissues, pp.567-604 (Cambridge Unis
