Transitional epithelium

Boyd, N.L. et al.. Human embryonic stem cell-derived mesoderm-Uke epithelium transitions to mesenchymal progenitor cells. Tissue Eng Part A, 2009.15(8) 1897-907. 

Celis JE et al. Proteomics and immuno-histochemistry define some of the steps involved in the squamous differentiation of the bladder transitional epithelium a novel strategy for identifying metaplastic lesions. Cancer Res 1999 59 3003-3009. 

In the small intestine, contact time with the absorptive epithelium is limited, and a small intestinal transit time (SITT) of 3.5-4.5 hr is typical in healthy volunteers. The Holy Grail of drug delivery would be to discover a mechanism that... 

In chronic studies, DMMP was administered by gavage in corn oil for up to 2 years at doses of 500 or 1000 mg/kg/day to rats and at doses of 1000 or 2000mg/kg/day to mice. " Survival in dosed male rats was reduced, due in part to renal toxicity. Lesions of the kidney included increased severity of spontaneous age-related nephropathy including calcification, hyperplasia of the tubular and transitional epithelium, tubular cell adenocarcinomas, and transitional cell papillomas and carcinomas. Similar lesions were not seen in female rats or in mice of either sex, although reduced survival in male mice prevented adequate analysis. The... 

WT1 is present in the metanephric mesenchyme before induction and is upregulated during induction. Blocking induction stops the production of WT1. WT1 is expressed at high levels during the condensation of the mesenchyme and its transition to epithelium. Its expression diminishes thereafter, except in the podocyte layer of Bowman s capsule. WT1 knockout mice do not develop kidneys. The metanephric mesenchyme from these mice cannot be induced by wild-type inducers. 

The transition from mesenchyme to epithelium involves biochemical changes in the cells and the extracellular matrix, N-CAM expression on cell surfaces disappears, replaced by L-CAM (uvomorulin). Vimentin, a characteristic cytoskeletal component of mesenchyme, disappears, and cytokeratin, characteristic of epithelia, appears. There is a decrease in collagen I extracellularly and an increase in the basement membrane components laminin and collagen IV. 

After epithelialization and the formation of the S-shaped tubule, there is still much that needs to occur in order for the nephron to function. Cells destined to form the podocyte layer of the glomerulus flatten out and lose some of the markers that characterized their earlier transition to epithelium, including c-MYC, HOX-c9, LFB-1 and LFB-3, while keeping a high level of WT1. Expression of more classical mesenchymal markers such as vimentin takes place, but the cells also keep a number of epithelial proteins such as desmosomal components. The result is a tissue that is more organized than most connective tissue but leakier than most epithelium, the optimum design for urine filtration. 

Hess RA (1990) Quantitative and qualitative characteristics of the stages and transitions in the cycle of the rat seminiferous epithelium light microscopic observations of perfusion-fixed and plastic-embedded testes. Biol Reprod, 43 525-542. 

Located on the edge of the transparent cornea, it maintains the junction with the opaque sclera. On the level of the epithelium, it is the transition between a multilayer scale-like corneal epithelium and a cylindrical conjunctival epithelium with two cellular bases, with continuity of the basement membranes. At the epithelial level, the cells of the comeal epithelium are gradually replaced by a conjunctival epithelium made of two layers of cylindrical cells accompanied by calyciform cells. 

Van Zyl et al. reported on the diffusion of ipratropium through porcine bronchial epithelium tissue [74], In principle, ipratropium is administered via the respiratory tract by inhalation to treat pulmonary diseases associated with bronchoconstriction. Therefore, pulmonary absorption by bronchial tissue determines its local efficacy and was thus investigated in a diffusion cell in vitro. Bronchial epithelium was equilibrated in PBS and discs of 4 mm2 were mounted on that diffusion cell separating the donor and receiver compartment. The donor compartment contained the drug dissolved in PBS (1 mg/ml) and the receiving chamber was permanently flushed with a low flow (1.5 ml/h) of PBS thus allowing time-resolved fractionation for subsequent direct analysis by LC-ESI MS/MS in MRM mode. Transition to the product ion at m z 124 was monitored for quantification (Table 9). The transfer of ipratropium was characterized by the flux (about 220 ng/cm2/min) and the permeability coefficient calculated to be 1.6 x 10-8 cm/s. 

The structure of the bladder, ureter, and urethra are similar in that they contain three layers, the mucosa, muscularis, and serosa. In the bladder (Figure 3.16) the inner layer (mucosa) when empty is infolded and it is made up of transitional epithelium. The lamina propria that is found below contains collagen and elastic fibers in the deeper layer. The muscularis is prominent and contains muscle fibers that are arranged in branching bundles separated by connective tissue. Muscular contraction causes expulsion of fluid from the bladder into the ureter. The connective tissue between the muscle fiber bundles merges with the connective tissue of the serosa. The serosa is continuous with the peritoneal lining. 

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