Cuboidal epithelial cells

The canaliculi continue into an ampulla-like extension known as Hering s canal (E. Hering, 1866). This area can be regarded equally as the end point of the canaliculi and the beginning of the ductules, hence the term intermediate ductule is used (M. Clara, 1930). From here the bile ducts have their own wall of cuboidal epithelial cells. They are 7-20 pm in diameter. Their designation as preductules has been generally adopted. (57) Because of their extreme proneness to damage, the preductules are described as the Achilles heel of the liver (L. Aschoff, 1932). 

Thyroglobulin is stored in the follicular lumen and must re-enter the cell, where the process of proteolysis liberates thyroid hormone into the bloodstream. Thyroid follicles active in hormone synthesis are identified histologically by columnar epithelial cells lining follicular lumens, which are depleted of colloid. Inactive follicles are lined by cuboidal epithelial cells and are replete with colloid. Both iodide and lithium block the release of preformed thyroid hormone, through poorly understood mechanisms. 

Metanephric adenoma of the kidney is a unique form of renal adenoma characterized by a proliferation of tubular and micropapillary to glomeruloid structures lined by bland cuboidal epithelial cells. The relatively high nuclear-to-cytoplasmic ratio of metanephric adenoma cells and their slightly amphophilic cytoplasmic coloration impart a typical blue low-power appearance to the neoplastic nodule. The latter is in contrast to the lighter eosinophilic appearance of its main differential diagnosis entity, namely the solid variant of papillary Like papillary RCC, metanephric adenoma can feature foamy histiocytes in papillary cores and occasional psammomatous calcifications. Helpful... 

In contrast to papillary ependymoma, the choroid plexus papilloma contains a layer of columnar to cuboidal epithelial cells over a basement membrane and fibrovas-cular stroma. The type IV collagen and laminin in this stroma contrast with ependymomas, which have solid parenchyma without collagen or laminin (see Tables... 

Histologic study shows that the histologic features of the thyroid gland of the iodine treated fetuses were comparable to normal control fetuses. In the 4th - 5th month fetuses, the thyroid gland showed distinct formation of follicles lined with small cuboidal epithelial cells and containing scanty colloid. In the 6th - 8th month fetuses, the thyroid tissue showed more mature differentiation. The follicle size and the amount and staining density of the colloid increased with the fetal age. 

In another approach, Parnigotto and coworkers reconstructed corneal structures in vitro by using corneal stroma containing keratocytes to which corneal epithelial cells from bovine primary cultures were overlaid [73], However, this particular corneal model did not contain an endothelial layer. This model was histochemically characterized and the toxicity of different surfactants was tested using MTT methods. This stroma-epithelium model has been reported to show a cornea-like morphology, where a multilayered epithelial barrier composed of basal cells (of a cuboidal shape) and superficial cells (of a flattened shape) is noted. Furthermore, the formation of a basement membrane equivalent and expression of the 64-kDa keratin were reported, indicating the presence of differentiated epithelial cells. The toxicity data for various surfactants obtained with this model correlate well with those seen by the Draize test [73], However, this corneal equivalent was not further validated or used as a model for permeation studies. 

A single layer of epithelial cells is termed simple epithelium, whereas those composed of more than one layer are termed stratified epithelia. Stratified epithelia are found in areas which have to withstand large amounts of wear and tear, for example the inside of the mouth, orthe skin. Epithelial cells may be, for example, squamous (flattened), columnar (tall), cuboidal (intermediate between squamous and columnar) and may contain surface specializations, such as cilia in the nasal epithelium and keratin in the skin. 

Appendageal structures commonly found within the skin are the hairs, hair follicles, associated sebaceous glands, apocrine and eccrine sweat glands, and arrector pili muscles. Hairs are formed by epidermal invaginations. These keratinized structures traverse the dermis and may extend into the hypodermis. The free part of the hair above the surface of the skin is the hair shaft, and the part deep within the dermis is the hair root, which forms an expanded knob-like structure called the hair bulb. This is composed of a matrix of epithelial cells in different stages of differentiation. Hair is composed of three concentric epithelial cell layers the outermost thin cuticle, a densely packed keratinized cortex, and a central medulla of cuboidal cells. The hair follicle consists of four major components (1) internal root sheath (internal root sheath cuticle, granular layer, pale epithelial layer) (2) external root sheath (several layers similar to the epidermis) (3) dermal papilla (connective tissue) and (4) hair matrix (comparable to the stratum basale of the epidermis). 

The respiratory part of the airways is also shielded by a ciliated epithelium. Along this region the ciliated cells are interspersed by Clara cells which are discussed as progenitor cells of the respiratory epithelium [8,9]. This epithelium has to be separated from the alveolar epithelium, which is a non-ciliated epithelium and formed by alveolar epithelial cells type I and type II. The major surface area of the alveoli is covered by type I cells. Nevertheless, the cuboidal alveolar type II cells represent about 90 % of the alveolar epithelial cells. 

In the separation of alveolar air space and blood circulation, the alveolar epithelium is a more restrictive paracellular barrier than the capillary endothelium. About one-third of the alveolar epithelial cells are type I cells, but these cells make up approximately 95% of the cellular surface area. The remaining two-thirds of the alveolar epithelial cells that comprise the remaining 5% of the cellular surface area are the surfactant-producing cuboidal type II cells.43,45,52 Type I cells have thin cytoplasmic extensions and exhibit a large number of plasmalemmal invaginations called caveolae, which may play a role in macromolecular and protein transport across the blood-air barrier of the lung.44,45,58,59... 

Although interspecies differences can be circumvented through the use of primary cultures of human alveolar epithelial cells, routine use of these cells is limited by availability.58,60 Primary culture of rat type II alveolar epithelial cells is economical and demonstrates high reproducibility, and its phospholipid secretion is similar to that of human type II cells.43 P-gp is expressed in both human and rat type I cells but not in freshly isolated rat type II cells.61 It is assumed that alveolar type II cells are progenitors for regenerating type I cells in vivo, and type II cells in culture lose their cuboidal appearance, lamellar bodies, and microvilli, and the number of surfactant proteins decrease. Monolayers are formed in 5 to 8 days, and the transdifferentiation to type I-like cells is complete within 7-8 days, characterized by the development of attenuations, tighter junctions, and increasing expression of... 

Epithelial cells are classified by their shape, stratification and specialization. The cell shape is subdivided into squamous, cuboidal, columnar and transitional ... 

On contact with a mucosal surface lined by colimmar, cuboidal, or noncornifled squamous epithelial cells, the gonococci attach to cell membranes by means of surface pUi and are then pinocytosed. The virulence of the organism is mediated primarily by the presence of pili and other outer membrane proteins. After mucosal damage is established, polymorphonuclear leukocytes (PMNs) invade the tissue, submucosal abscesses form, and purulent exudates are secreted. "... 

Some epithelial mesotheliomas are composed of small cysts formed by uniform cuboidal mesothelial cells and associated numerous blood vessels (Fig. 12.68). This type of mesothelioma may be difficult to differentiate from a vascular neoplasm. The epithelial mesothelial cells may contain intracytoplasmic hemosiderin (Fig. 12.69). The immunophenotype of such neoplasms is identical to that of other epithelial mesotheliomas. The vascular proliferation may be related to an endothelial growth factor produced by neoplastic mesothelial cells.Adenomatoid tumors are localized benign mesothelial proliferations that most frequently occur in the epididymus and cornua of the uterus.Adenomatoid tumors have been identified in the adrenal gland and pancreas. These tumors are formed by uniform small cuboidal cells and can appear invasive. They express keratin and other markers of mesothelial cells and have the characteristic ultrastruc-tural features of mesothelial cells. Adenomatoid tumors have also been reported in the pleura. Hyperplastic... 

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