ISSN:1059-910X    

DOI:10.1002/jemt.1070320202

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractAmphibians living partially or totally in a terrestrial environment are the first tetrapods to possess parathyroid glands. Purely aquatic amphibians and amphibian larvae lack these endocrine glands. The parathyroids develop at the time of metamorphosis. The parathyroid glands in caecilians consist of a single cell type, that of urodeles may be composed of basal (supporting) cells and suprabasal (chief) cells, and that of anurans of small and large chief cells. Parathyroid glands of caecilians and anurans lack connective tissue, blood vessels, and nerves. The parathyroid cells become activated in response to decreased blood calcium concentration and undergo changes indicating increased parathyroid hormone secretion. Increased blood calcium concentration suppresses secretory activity. Usually, parathyroidectomy elicits hypocalcemia in most amphibians. Such operations have no effect in lower urodeles. Parathyroid hormone administration provokes hypercalcemia in most amphibians. The parathyroids of caecilians have not been studied in detail. The urodeles and anurans exhibit seasonal changes in the parathyroid glands. These changes may be initiated by environmental stimuli such as light, temperature, or alterations in blood calcium levels caused by natural hibernation. © 1995 Wiley‐Liss, I

ISSN:1059-910X    

DOI:10.1002/jemt.1070320203

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractAdult reptiles possess one or two pairs of parathyroid glands that have been shown in many species to derive from the third and fourth pharyngeal pouches, respectively. Up to five pairs may develop during early embryonic life. Excess glands may involute during late embryogenesis. The location of the parathyroid glands differs in the various species. As a general rule, they lie just anterior to the heart, the anterior pair (parathyroid III) being associated with the carotid artery, the posterior pair (parathyroid IV) with the aortic arch. In snakes, however, the anterior pair (parathyroid III) is associated with the carotid artery near the angle of the jaw. As shown by light microscopy and, to a lesser extent, by electron microscopy, the parathyroid parenchyma comprises secretory cells which may form dark and light variants, occasional oxyphil cells, and stellate cells. They are arrangend in cords separated by connective tissue containing a capillary network. Parathyroid secretory cells often form follicles which might be the result of degeneration. Degeneration may occur as a form of involution during winter in species undergoing seasonal changes. The product of parathyroid cells, the parathyroid hormone, is responsible for the maintenance of blood calcium concentration. The sites of action—bones, kidneys, intestine, endolymphatics, and dermal skeleton—are not well understood or not investigated. In some turtles, parathyroid hormone is not the (main) factor for the regulation of calcium homeostasis. © 1995 Wiley‐Lis

ISSN:1059-910X    

DOI:10.1002/jemt.1070320204

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractBlood supply and microvascular patterns of Stannius corpuscles were studied by scanning electron microscopy of vascular corrosion casts in the teleost fishesBlennius pavo, Zosterisessor ophiocephalus, andGasterosteus aculeatus. Microvascular casts demonstrated that Stannius corpuscles—depending on their location—have an arterial supply derived either directly from the dorsal aorta, from the trunk of the first ventral segmental artery of the tail, or from a renal artery. Supplying arteries form a capsular capillary bed and a parenchymal capillary bed; both are composed of fine, freely anastomosing vessels with a homogeneous isotropic distribution. Central venules arise deep in the corpuscles. In the capsule, they form a single vein which drains into a segmental vein or directly into the caudal vein. Stanniocalcin, the hormone of the Stannius corpuscle, enters the renal circulation and reaches its main target organs, the gills, via posterior cardinal veins—heart—ventral aorta. Occasionally, some capsular venules empty into the trunk kidney peritubular venules. Capillaries are fenestrated and are embraced by pericytes with long, slender processes. The perivascular space contains collagen fibrils. Nerve fibers are found close to endothelial cells and pericytes. Vascular patterns of Stannius corpuscles are compared with those of the rat parathyroid glands and are discussed in respect to physiological implications. © 1995 Wiley

ISSN:1059-910X    

DOI:10.1002/jemt.1070320205

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractThe blood vascular bed and pericapillary space of the rat parathyroid gland were studied by scanning electron microscopy of vascular casts, freeze‐cracked tissue blocks, and NaOH‐treated tissue specimens. The findings were supplemented by transmission light and electron microscopy of sectioned tissue samples. The rat parathyroid gland contained a rich network of freely anastomosing capillaries. These capillaries were surrounded by marked pericapillary spaces that were demarcated by basal lamina of both capillaries and parenchymal cells. The pericapillary spaces contained many collagen fibrils and frequently issued some projections running deep into the sheets of parathyroid cells. The latter projections may be useful to supply the parenchymal cells located far from the capillaries. The collagen fibrils may regulate the flow of tissue fluid in the pericapillary space and convey parathyroid hormone, which is released at the apicolateral domain, into the capillaries. © 1995 Wiley‐Lis

ISSN:1059-910X    

DOI:10.1002/jemt.1070320206

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractFixation with aldehydes is achieved either by immersion or perfusion. The parenchyma of parathyroid glands fixed by immersion consists of dark cells containing a lot of membranes of those organelles which are concerned with hormone secretion, light cells which are poor in these organelles, intermediate forms between the two, and multinuclear syncytial cells. They have been attributed to represent different functional stages of secretory activity, the dark cell being in an active form, the light cell in a resting form. Studies of the parathyroids of mice, rats, rabbits, cats, dogs, pigs, cattle, sheep, goats, and horses employing various fixation protocols clearly demonstrate that light cell variants and multinuclear syncytial cells are formed during improper immersion fixation as a result of membrane disintegration. Parathyroids fixed by perfusion or by immersion in an appropriate fixation medium comprise only one cell type which correspond to the dark chief cell. Parathyroid cells are polar cells bearing some of the rough endoplasmic reticulum in the basal pole, the rest of it, the Golgi complex, and secretory granules in the apical pole. The secretory product is released by exocytosis at the apicolateral domain of the plasma membrane into the intercellular space. Secretory activity can be altered experimentally, leading to drastic changes in the amount of cell membrane related to hormone synthesis, intracellular transport, exocytic release, and secretion coupled membrane retrieval. The sensitive reaction of parathyroid cells to both the mode of fixation and to fixation media demands careful evaluation of the fixation protocol. This and the polarity of parathyroid ceils have to be borne in mind for estimating secretory activity on the basis of morphological criteria. © 1995 Wiley‐Liss, I

ISSN:1059-910X    

DOI:10.1002/jemt.1070320207

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractThe ultrastructure of the rat parathyroid has been under study for more than 35 years, but controversies still exist, especially regarding structure‐function relationships. The present review focuses on recent morphological parathyroid research on rats under normal conditions and in various states of disturbed calcium metabolism. To facilitate discussions on functional aspects, current biochemical data, particularly those dealing with the regulation of parathyroid hormone synthesis and release, are also considered. Our results from quantitative studies and from investigations employing serial sectioning form the basis for the discussions. A central issue is whether the parathyroid secretory cells undergo secretory cycles. Prompted by results obtained from improved fixation procedures and serial sectioning, we question the basis for the theory of secretory cycles. Since the rat parathyroid secretory cell is polar, a single section is not an appropriate sample for estimating functional activity and for comparing the structure and distribution of intracellular components of adjacent cells. The heterogeneity in ultrastructural appearance of intracellular vesicles calls for the use of specific markers in relating the structure of the vesicular compartment to intracellular processing of hormone. The importance of unbiased quantitative techniques is illustrated in discussions on cell number and size for estimating the response of the parathyroid gland to different functional states or disorders demanding changes in secretion of parathyroid hormone, e.g., hyper‐ and hypocalcemia. © 1995 Wiley‐Lis

ISSN:1059-910X    

DOI:10.1002/jemt.1070320208

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractBoth prosecretory and storage granules are concomitantly formed at the trans Golgi network including the innermost Golgi cisterna. Prosecretory granules develop into small secretory granules that release their contents by exocytosis finely regulated by a complex mechanism for maintaining calcium homeostasis. In the rat parathyroid cells, storage granules are large secretory granules storing parathyroid hormone for an emergency supply. The hormone is rapidly discharged by exocytosis when serum calcium concentration is decreased. The granules are constantly produced even under conditions of low serum calcium concentration in the regions of 8 mg/dl. The granule content is constantly hydrolyzed when not discharged, leading to a decreased core and finally to the formation of vacuolar bodies. The fate of the vacuolar bodies is unknown. Hypercalcemic conditions accelerate hydrolysis. The threshold value of calcium concentration required for the release of storage granule contents is between 8.0 and 7.5 mg/dl and that of calcium concentration for accelerating degradation of storage granules is about 11.5 mg/dl. Sympathetic stimulation causes storage granules to be discharged regardless of hypercalcemia or hypocalcemia. Parasympathetic stimulation accelerates hydrolysis. The degradation of storage granules seems to be closely associated with an intracellular regulatory mechanism for parathyroid hormone secretion. © 1995 Wiley‐Liss, I

ISSN:1059-910X    

DOI:10.1002/jemt.1070320209

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractParathyroid glands (n = 271) removed from 130 patients were examined by light and electron microscopy. A standardized method of tissue processing was employed and morphometry was performed. The aim of the paper is to provide a description of the human parathyroid chief cell ultrastructure in health and disease, with quantitative evaluation of structures involved in secretion of parathyroid hormone in a large case series, and to discuss their role in current diagnostic histopathology. The patients were euparathyroid (n = 10), or affected by primary (n = 97), secondary (n = 8), or tertiary (n = 15) hyperparathyroidism. In normal glands, solid parenchyma was composed of chief cells, large clear cells, transitional‐oxyphil cells, and oxyphil cells. Chief cell hyperplasia, pseudo‐adenomatous hyperplasia, adenoma, water‐clear cell hyperplasia, and carcinoma were the most usual forms of parathyroid disease responsible for primary hyperparathyroidism. In chief cell hyperplasia, all the parathyroid glands were enlarged and the chief cells were in an active state of hormone secretion, with a large Golgi complex, abundant rough endoplasmic reticulum (RER), small lipid droplets, and tortuous plasma membrane. In pseudo‐adenomatous hyperplasia, one gland was enlarged and the others displayed a normal size; however, electron microscopic examination and morphometric analysis showed that all the glands had active cells. Adenomas displayed a pattern similar to those of pseudo‐adenomatous hyperplasia, with one gland enlarged and the others of normal size. However, ultrastructural examination and morphometry showed that the normal‐size glands were hypo‐active. Water‐clear cell hyperplasia showed cells filled with cytoplasmic vacuoles. In these cells, structures with intermediate features between secretory granules and vacuoles were visible. Nucleo‐cytoplasmic atypias were frequently visible in parathyroid carcinoma cells. In secondary and tertiary hyperplasia, active chief cells were regularly mixed with oxyphil or transitional‐oxyphil cells. The tertiary hyperplasia was characterized by RER‐associated structures that were not found in the normal or other pathologic conditions. These results demonstrate that electron microscopy and morphometry represent useful tools in parathyroid histopathology.

ISSN:1059-910X    

DOI:10.1002/jemt.1070320210

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

ISSN:1059-910X    

DOI:10.1002/jemt.1070320201

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY