Electron Microscopic Studies of the Follicle Cells in the Thyroid Gland of the Dog

Abstract

The follicle cells of the thyroid gland of the dog were studied by electron microscopy, in combination with the effects of treatment with thyroid stimulating hormone, and the following results were obtained.
1. The follicle cells have a considerable number of microvilli extending from their apices into the colloid and rarely a central flagellum. 2. Just below the apical plasma membrane, the superficial cytoplasmic zone is found, free of secretory granules, mitochondria and rough-surfaced endoplasmic reticulum, and contain more or less numerous small membrane-bound vesicles. The vesicles remain in question whether they take their origin from pinocytosis or others. 3. The rough-surfaced endoplasmic reticulum is abundant, especially in the basal half of the cell body, usually dilated and contain a substance resembling follicle colloid. The ribonucleoprotein particles are well-formed especially in the part in close contact with the mitochondria, while they are absent or sparsely distributed in the part in contact with the Golgi complex. 4. The Golgi complex lies in the supranuclear zone and consists of several paired membranes arranged in layers, a considerable number of small vesicles and a number of vacuoles. Some of the small vesicles resemble small secretory granules and suggest transitions to the latter. 5. Secretory granules are different in size and density, and move from the Golgi zone towards the apical zone. Some are directed towards the basal plasma membrane. Their further fate can not be followed. 6. The mitochondria show oval to rod-shaped profiles and are abundant, especially in the basal half of the cell body. The mitochondria show a close topographic relation to the rough-surfaced endoplasmic reticulum and are often corn-. pletely enclosed by the latter. They contain well-formed cristae mitochondriales which are arranged perpendicularly to their long axis. 7. The nuclei show no special characteristics. 8. Treatment with thyroid stimulating hormone induces tremendous dilation of the rough-surfaced endoplasmic reticulum and increase of secretory granules, but no significant change in other organelles. 9. No relation between the process of colloid resorption and the organelles could be established morphologically. 10. The significances of the different organelles were discussed in relation to secretion and release.