A study by light and scanning electron microscopy of the lining epithelium of the guinea pig bladder following artificial ulceration

Abstract

Following artificial ulceration of the guinea pig bladder epithelium, study by light microscopy showed that mitotic activity occurs within 24 hours in the basal layer of the remaining epithelium; which leads to thickening, disorganization and cell shedding. At the ulcer margin, the epithelium forms a rolled edge, from the extremity of which a two-layered sheet of flat cells grows over the edematous ulcer bed, and the ulcer site is protected during dilation of the bladder by localized muscle spasm. Healing is effected within about one week, as the mitotic activity declines. Organization of the new epithelium commences at the periphery and the cells acquire glycogen and alkaline phosphatase. Study by SEM, which included normal bladders, confirmed that new epithelium spreads from a rolled epithelial edge, and also showed that cells undergoing rejection have globular profiles with surface microvilli. The immature epithelial cells are markedly distorted from mutual pressure during migration and their surfaces show only short microvilli. Ulcers heal after four to seven days, depending on size, and the new cells rapidly assume the pentagonal and hexagonal outlines and the reticular pattern of surface ridges, characteristic of mature surface cells. The ridges apparently develop by fusion of rows of microvilli. By the tenth day it is difficult to identify the original ulcer site.

Development and Maturation of the Bladder Epithelium of the Guinea Pig

“…Pre sumably, fusion of the microvilli, together with the linkage of the rows, produces the reticular pattern of ridges. A similar se quence was observed in new cells, formed after artificial ulceration of the bladder epithelium [Wong and Martin, 1977b], It may therefore be concluded that the mat uration of the surface cells in the fetus is similar to that observed in the new cells formed after injury in the adult.…”

“…However, since the same process occurs in adult transi tional epithelium when mitotic activity is stimulated, either by acute distension of the bladder [Martin, 1972] or by artificial ulcer ation [ Wong and Martin, 1977b], it is sug gested that it results from overproduction and consequent overcrowding of cells.…”

“…This was further borne out by a study of the repair processes following artificial ulceration of the epithelium [ Wong and Martin, 1977b]. It was found that the new surface cells of the epithelial sheet, which grows from the rolled ulcer margin over the raw bed, have a smooth appearance and show only short microvilli as a surface feature.…”

The Surface of the Conjunctiva in Domestic Ruminants

“…Others differ entiate between microvilli and microplicae or ridges [Wong and Martin, 1977;Mills and Malick, 1978;Hodgkins et al, 1978: Pfister andRenner, 1978;Malczak, 1980]. In the conjunctival epithelium of domestic ruminants we were able to clearly find two types of cyto plasmic projections.…”

“…In the urinary bladder epithelium, Wong and Martin [1977] found microvilli on immature surface cells, and microplicae in mature cells. The same authors postulate that microplicae originate from microvilli that have grown together.…”