Binucleate cells of transitional epithelium (bladder)?

Question

Working through Histology slides of the transitional epithelium (urothelium) of the urinary bladder, I noticed that the dome-shaped cells at the top of the transitional epithelium are frequently binucleate. In doing research, I found that the top cells of the transitional epithelium are 'often binucleate and usually polyploid'

Why is this? What purpose does this serve?
Is the binucleate feature consistent enough across slides to be used as a common identifying feature to recognise transitional epithelium from the urinary tract? Is the absence/over-abundance of binucleate cells characteristic of certain diseases?

I also see prominent granules (of glycogen, I presume?) in these cells.

Is this glycogen? & What purpose does this serve?

Also, I'm having difficulties recognising transitional epithelium in slides. Does anyone have any tips to share on how to easily recognise transitional epithelium as such (common features to look out for, etc.), especially in distinction to pseudo-stratified epithelium, which often looks similar?

Answer 1

In other stratified epithelium, it is the basal cells that replicate to replace the cells lost in the top layers. In transitional epithelium, which is also a stratified epithelium, the most superficial layer of cells are replaced or turnover occurs because of mitosis of the superficial facet cells themselves. In this case it is not unusual to see dividing cells in its last stage of division as a large cell containing two nuclei, which soon that cell will be 2 cells.