Hisao Fujita

Fine structure of the thyroid gland.

Publisher Summary This chapter discusses the fine structure and functional properties of the thyroid gland. The thyroid gland consists of numerous ball-like structures called follicles, and of interfollicular connective tissues with blood capillaries. Each follicle is composed of numerous follicular epithelial cells arranged as a simple cuboidal epithelium, a lumen surrounded by the epithelial cells, and a few parafollicular cells located singly or in groups in the basal part of the follicular epithelium. Each follicular lumen surrounded by the follicular epithelium is a completely enclosed area, storing colloid materials (thyroglobulin) secreted by the epithelial cells. The secretory process of T 3 and T 4 , consists of several complicated steps: (1) synthesis of a large molecular glycoprotein called thyroglobulin in the follicular epithelial cells, (2) release of thyroglobulin into the follicular lumen, (3) iodination of the tyrosyl residues of thyroglobulin, (4) reabsorption of thyroglobulin from the follicular lumen into the follicular epithelial cells,(5) hydrolysis of thyroglobulin for the liberation of T 3 and T 4 , and (6) release of T 3 and T 4 from the follicular epithelial cells into the connective tissue space. The fine structure of the thyroid follicular epithelial cell is outlined.

Electron-microscopic studies on the development and aging of the oviduct epithelium of mice.

SummaryThe fine structure of the oviduct epithelium of the newborn to the old mouse was studied with an electron microscope. Just after birth, epithelial cells lining the ampulla of the mouse oviduct are simple columnar in shape and of one type in fine structure. They contain numerous free ribosomes, an extremely poor rough endoplasmic reticulum, and a small Golgi complex. In the 3-day-old mouse, the epithelial cells are differentiated neither into ciliated nor secretory cells, and are characterized by the appearance of many autolysosomes and a solitary cilium.The ciliary cells differentiates 5 days after birth. Ciliogenesis is frequently observed at 5–10 days. The important role of the fibrous granules for ciliogenesis and that of the Golgi apparatus for membranogenesis of the cilia are described and discussed.The secretory cell having mucous secretory materials is differentiated at 23 days.In the epithelial cell lining the ampulla of the aged (22 to 24-month-old) mouse oviduct, large autolysosomes and vacuoles 2–6 μm in diameter occur in the ciliated cell, though cilia and other cell organelles are well preserved. In the old mouse the secretory granules almost disappear and the rough endoplasmic reticulum is strikingly dilated in the secretory cell.No features showing the transformation between the secretory cell and the ciliary one are seen in the mouse oviduct.

Fine structural localization of peroxidase in the rat thyroid

SummaryThe fine structural localization of a peroxidase activity in the rat thyroid follicular epithelial cell was studied by histochemistry at electron microscopic level. The reaction product is recognized chiefly in the cisternae of the elements of granular endoplasmic reticulum and of nuclear envelope. Golgi vesicles or apical small vesicles, mitochondria, and dense granules are sometimes positive for this reaction. The relationship between the fine structural localization of peroxidase and the site of the iodination of thyroglobulin is discussed.

Electron microscoic studies on the development of the thyroid gland of chick embryo

SummaryNormal thyroid glands of White-Leghorn chick embryo, ranging in age from 6 to 17 days of incubation were studied with the light as well as electron microscope.1.By light microscopy, the thyroid tissue from 6 to 10 days of incubation consists of the epithelial cell cord and the loose mesenchyme, and the PAS-positive droplets begin to be found distinctly throughout the epithelial cell cord in a 9 day-old embryo.2.By electron microscopy, the thyroid cell of a 7 day-old chick embryo is characterized by numerous abundant polysomes. Though a few mitochondria and small Golgi area are noticed, the rough-surfaced endoplasmic reticulum is very poor. This structure is developed more and more with increase of incubating days.3.In an 8 day- (rarely in a 7 day-) old embryo, the primitive follicle lumen appears between two epithelial cells. Fairly long microvilli are well developed and a terminal bar forms a ring at the edge of the lumen. Around the lumen are numerous small vesicles considered to be derived from the Golgi field. The developmental endoplasmic reticulum, the Golgi apparatus lying near the lumen, numerous vesicles which might be derived from the Golgi region, a central flagellum projecting from the epithelial cell, and an appearances of the terminal bar are considered to be important elements in making up the primitive follicle lumen. In a few cases, the primitive follicle lumen has a shallow intracellular bay or extension which could be interpreted as an intracellular follicle lumen.4.A few small dense granules suggesting lysosomes appear at 8 days (rarely at 7 days) of incubation in or near the Golgi region.5.A few large intracellular less dense droplets are first found near the primitive follicle lumen at 10 days of incubation. It is not yet solved whether this droplet is a secretory substance or a resorbed one.6.By mitosis of the epithelial cells and fusion of the follicle lumens, the primitive follicle lumen enlarges with increase of days. The loose mesenchyme begins to penetrate into the epithelial cell cord to make up each follicle at 10–11 days of incubation, and the typical follicle is mostly completed at 14 days of incubation.7.All the mesenchyme cells including the endothelial cell and connective tissue cell are characterized by abundant polysomes and poorly developed cytomembrane system. The rough-surfaced endoplasmic reticulum is developed more and more with incubating days in the endothelial as well as connective tissue cells. Rerely, a round cell, high in electron density, suggesting an erythroblast is seen in contact with the endothelial cell in 7–9 days old embryos.

Studies on the iodine metabolism of the thyroid gland as revealed by electron microscopic autoradiography of125I

ZusammenfassungDer Jod-Stoffwechsel der Schilddrüse wurde mit I125 bei erwachsenen Mäusen und Hühner-Embryonen mit elektronenmikroskopisch-autoradiographischen Methoden untersucht.Bei Mäusen erschienen die Silberkörnchen vorwiegend im Lumen der Follikel bereits 3 min nach der intraperitonealen I125-Injektion und nahmen dann im Laufe der Zeit zu. Nur wenige Körner waren zwischen 3 min und 2 Std nach der Injektion von radioaktivem Jod in den Follikelzellen, und zwar im Golgi-Apparat und im apikalen Cytoplasma nachweisbar. Die Jodierung des Thyreoglobulins bei der Maus findet also offenbar zum größten Teil im Follikellumen und an der Zelloberfläche statt. Demgegenüber scheinen die Befunde bei Hühner-Embryonen zu beweisen, daß die Jodierung des Thyreoglobulins nicht nur im Lumen der Follikel, sondern auch im Cytoplasma erfolgen kann. Bei 10, 13 und 18 Tage alten Hühner-Embryonen waren 15–60 min nach der I125-Injektionen im Cytoplasma der meisten Zellen einige Silberkörnchen, und zwar besonders im Bereich des Golgi-Apparates, im apikalen Cytoplasma, im Ergastoplasma und in etwas größerem Umfang auch im Follikellumen, nachweisbar. 24 Std nach der Injektion befanden sich die meisten Silberkörnchen in den Lumina der Follikel.24 Std nach der I125-Injektion fanden sich im Lumen der Schilddrüsenfollikel der Maus viele Silberkörnchen, die 1–2 Std nach Injektion von TSH in den intracellulären großen Kolloidtropfen erscheinen. Dieser Befund weist darauf hin, daß die großen Kolloidtropfen offenbar aus dem Follikellumen rückresorbiert wurden.Einige Silberkörnchen wurden über der basalen cytoplasmatischen Matrix, über der basalen Plasmamembran und dem pericapillären Raum gefunden. Diese Beobachtungen weisen auf die Ausscheidung des Thyroxins und des Trijodothyronins in die pericapillären Räume hin.Bei den vorliegenden experimentellen Untersuchungen wurden keine Silberkörnchen in parafollikulären Zellen gefunden.SummaryThe iodine metabolism of the thyroid glands of adult mice and chick embryos was studied by electron microscopic autoradiography using125I.In the mouse silver grains appeared over the lumen of the thyroid follicle 3 minutes after intraperitoneal injection of125I and increased in number with time. No grains were detectable over most follicular cells of the mouse; occasionally a few grains were found over the cytoplasm, especially over the Golgi apparatus and apical cytoplasm of rare follicular cells, from 3 minutes to 24 hours after injection of125I. Thyroids of chick embryos 10, 13, and 18 days old, however, disclosed several silver grains over the cytoplasm, especially over the Golgi apparatus, over the apical cytoplasm with small vesicles, over the rough endoplasmic reticulum, and over the follicle lumen at 15, 30, 45 and 60 minutes after injection of125I. Most silver grains accumulated over the lumen of the follicle 24 hours after injection of radioactive iodine.It is concluded that in the adult mouse the iodination of the thyroglobulin takes place almost entirely in the follicular lumen and the cell surface. From the results of the studies on the chick embryo, however, the author considers that iodination in the thyroid cell may also occur.At 24 hours after injection of125I, the follicular lumen of the adult mouse showed numerous silver grains which appeared over large semi-dense to dense cytoplasmic droplets 1 to 2 hours after the injection of TSH. These results indicate that the large droplets represent the colloid reabsorbed from the follicle lumen.A small number of grains were found over the cytoplasmic matrix of the basal region, over the basal plasma membrane, and over the pericapillary space in mice under this experimental condition. The mechanism of the release of thyroxine and triiodothyronine was discussed.No grains were detectable over parafollicular cells of any of the adult mice studied.

On the fine structure of corpuscles of Stannius of the eel, Anguilla japonica.

SummaryThe Stannius corpuscle of the eel (Anguilla japonica) consists of numerous ovoid or polymorphic lobules separated by loose connective tissue containing blood capillaries. Each lobule is composed of a number of columnar secretory cells, containing numerous secretory granules, and arranged more or less radially. Each secretory granule, spherical, 0.5–1.0 μ in diameter, and osmiophilic, is surrounded by a limiting membrane derived from the Golgi membrane. The well developed rough-surfaced endoplasmic reticulum is closely associated with the Golgi field. Some Golgi elements might also be intimately associated with the outer nuclear membrane. Numerous glycogen particles are distributed throughout the cytoplasm. The secretory granules which tend to accumulate near the basal part of the cell might be released into the loose connective tissue. From these facts, the corpuscles of Stannius are considered to be protein-secretory endocrine glands without any similarity to the adrenal gland.

Electron microscopical studies on the thyroid of a cyclostome, Lampetra japonica, during its upstream migration

SummaryElectron microscopical studies were made of the thyroid gland of an adult lamprey, Lampetra japonica, in the upstream migration period.The thyroid consists of many usual follicles containing the colloid in their lumina, and a large parafollicle without colloid. The paper concerns only the usual follicle.The follicle cells found in the usual follicle wall are classified into three types; 1. a non-ciliated taller cell, 2. a ciliated taller one, and 3. a non-ciliated cuboidal one. From their cytoplasmic fine structure, it is considered that all these cells are essentially identical and differences among them are due to their functional state.All these type cells are characterized by irregularly developed interdigitations and aggregates of tonofilaments throughout the cytoplasm, especially in the perinuclear region. Although the rough-surfaced endoplasmic reticulum and the Golgi apparatus are fairly well developed in the first and second type cells, the cisternae are not so large-vacuolated but flattened, and the cytoplasm is more compact as compared with that of the higher vertebrate. In the third type cell, the cytomembranes are poorly developed.Large dense inclusion-bodies consisting of heterogeneously dense materials, of lamellar structures, and of less dense vacuoles, which are found often in taller follicle cells, are also characteristic for the lamprey thyroid. The body which might be intimately related to the Golgi apparatus is considered to be a kind of lysosomes and it perhaps corresponds to the yellow pigment observed by light microscopy.In the apical part of the cytoplasm in taller cells, there are three kinds of granules or vesicles; numerous small vesicles considered to be derived from the Golgi apparatus, a few small dense granules which seem to originate from the Golgi region, and a few large less-dense granules.In the third type cell, the cytomembranes are not so well developed as those of the first and second type cells. The large heterogeneously dense bodies and the cytoplasmic granules are very few in number.Around the follicle of the lamprey thyroid, there are a dense basement membrane and a relatively compact connective tissue with few blood capillaries. Characteristic fat cells are found in the connective tissue.

LIGHT AND ELECTRON MICROSCOPIC STUDIES ON THE DEVELOPMENT OF PERIPORTAL BILE DUCTS OF THE HUMAN EMBRYO

In order to clarify the development of periportal bile duct in the human embryo, the liver tissue of a 13 week‐old human embryo was studied using the electron as well as light microscope.

Freeze-fracture images of exocytosis and endocytosis in anterior pituitary cells of rabbits and mice.

SummaryFreeze-fracture images of exocytosis and endocytosis were studied in various kinds of secretory cells of the anterior pituitary of mice and rabbits. Exocytotic figures are frequently observed in thin section of the anterior pituitary cells. In freeze-fracture images, small elevated membrane areas without membrane particles are often seen on the PF of the plasma membrane of the secretory cells. There is a secretory granule in the cytoplasm just beneath the particle-free membrane area, and limiting membrane of the granule is also devoid of the membrane particles at the part facing the plasma membrane. The fusion of membranes for exocytosis may occur at this particle-free area.The limiting membrane of the granule which is continuous with the plasma membrane is almost always coated after release of the granule core. This invagination of coated membrane may be an initiation site for the membrane retrieval after exocytosis. In freeze-fracture images, this depressed region with an accumulation of the membrane particles is observed on the PF of the plasma membrane. This particle-rich depressed region is thought to correspond to the coated area of the plasma membrane observed in thin section. It is thought that the membrane retrieval by pinocytosis initiates at the particle-rich depressed region of the plasma membrane.

Fine structural localization of thiamine pyrophosphatase and acid phosphatase activities in the mouse pancreatic acinar cell.

SummaryThe fine structural localization of thiamine pyrophosphatase (TPPase) and acid phosphatase (AcPase) was examined in pancreatic acinar cells of fasting and fed mice. The results were not affected by these conditions. TPPase activity was positive in two and sometimes three cisternae of the inner Golgi lamellae as well as in the condensing vacuoles of the trans area, but negative in the rigid lamellae and small vesicles of the trans area. AcPase activity was demonstrated in two and sometimes three cisternae of inner Golgi lamellae, condensing vacuoles, rigid lamellae, lysosomes and smooth or coated vesicles in the trans area. The inner Golgi lamellae and the condensing vacuoles were positive for both enzyme activities. From these facts, the lysosome is considered to be formed not only in the GERL system but also through the rough endoplasmic reticulum-Golgi apparatus route. It is reasonable to consider that Novikoffs GERL is not independent from the Golgi apparatus but represents a part of this organelle.