Question

Describe the histology of the urinary tract and how that changes between the ureter and the renal tubules.

Answer 1

Histology of Urinary tract-

Urinary tract cytology is almost exclusively concerned with evaluation of the urothelium that lines the urinary bladder and other excretory passages namely, the renal pelves, ureters, and portions of the urethra. The epithelium is adaptable to the changing volume and permits the storage and discharge of the urine. This transitional cell epithelium is highly specialized and uniform but does include epithelial buds, subepithelial often centrally cystic nests (the nests of Brunn), and areas of squamous metaplasia or squamous variance. The transitional epithelial cells have unique ultrastructural features including surface folds believed to provide additional plasma membrane during bladder expansion and robust junctional complexes that provide a watertight seal. The predominant transitional cell epithelium or urothelium in the calices is two or three cells thick, in the ureters is four or five, and in the empty bladder is lined by six to eight layers of transitional cells. Three cell types are recognizable by light microscopy. These are the large, often binucleated or multinucleated superficial cells covering the cells that form the lower portions of the epithelium-like umbrellas. The underlying intermediate pyramidal cells are smaller and somewhat elongated. A layer of even smaller cuboidal cells with little cytoplasm is located adjacent to the basement membrane. The three cell types can be distinguished by flow cytometry and by different patterns of lectin binding. These cells can also be well defined by morphologic examination of urine specimens. The superficial cells are characterized by a shape maintained by a rigid surface membrane . They have an acidophilic cytoplasm. Many are binucleated and some (approximately 3%) are multinucleated. The nuclei are large and are likely to undergo reactive change. The intermediate and basal cells are similar and have well-developed desmosomal connections and a plasma membrane that is folded in the empty bladder. It is capable of unfolding when the bladder becomes dilated. The arrangement of these cells is regular, with their long axis perpendicular to the basal membrane. Their cytoplasm contains glycogen, often resulting in a clear appearance during processing. The superficial cells also contain glycogen and sometimes mucus.

The Glomerulus filters a protein-free and blood-free filtrate which is then scavenged through the tubules where active and passive transport returns electrolytes and glucose to the bloodstream. The final product has been reduced to what we call URINE.