The kidney, covered by a connective tissue capsule, is divided into two main components; an outer cortex and an inner medulla.

The cortex (left of slide) contains numerous glomeruli (or renal corpuscles), renal tubules and blood vessels. At relatively low power, circular glomeruli surrounded by a clear area called Bowman’s capsule (or space) can be seen. At high power, glomeruli are seen to be composed of bundles of capillaries lined by fenestrated endothelial cells. The endothelial cells lay on a basement membrane whose outer surface is lined with podocytes. Mesangial cells are dispersed throughout the capillary tuft. Parietal epithelial cells line the outer wall of Bowman's capsule. At high power, afferent and efferent arterioles may be seen entering and leaving the glomeruli, respectively. The remaining cortical parenchyma is filled with renal tubules. Proximal convoluted tubule cells are columnar, acidophilic and have densely packed microvilli at their luminal surface, creating a brush border. Distal convoluted tubule cells are cuboidal and have no brush border. Use these characteristics to distinguish between tubules in this slide. The macula densa is the point of contact between the distal convoluted tubule and the glomerular afferent arteriole.

The medulla (right of slide) is composed of pyramid-shaped units called medullary pyramids with convey collecting ducts from numerous nephrons. Collecting ducts, have a simple cuboidal epithelium. Glomeruli are not seen in the medulla.



Acute pyelonephritis:

Extensive infiltration of polymorphonuclear leukocytes (PMNs) is seen in renal tubules, as well as in the interstitial tissue in this slide. PMNs (mainly neutrophils) are blood cells with tri-lobed nuclei. Tubules may be necrotic. The glomeruli appear relatively normal.



Chronic pyelonephritis:

Chronic interstitial and tubular inflammatory infiltrate can be identified in this section of chronic pyelonephritis. Some of the tubules appear atrophied, dilated, and contain eosinophilic hyaline casts. The tubules are surrounded by interstitial fibrosis.



Renal cell carcinoma:

The section on the left side of the slide, at low power, demonstrates pale islands of neoplastic cells along the left border of the section. This is a malignant tumour of renal tubular and ductal epithelial cells. At high power, the tumour cells are large with abundant clear cytoplasm and central nuclei. The remaining kidney darker staining renal cortex appears normal (see kidney above).



Wilm's tumour:

A malignant neoplasm composed of stromal (less cellular area), epithelial (spindle-shaped cells) and blastemal (tightly packed small blue round cells) elements.




The ureter is the darker stained circular structure located near the centre of this tissue section. It’s lumen in lined by multiple layers of transitional/urothelial cell epithelium. The top layer of cells are the largest and are called umbrella cells. The deepest layer of cells are the smallest, appear crowded and are called basal cells. The epithelium lies on a dense collagenous lamina propria and three smooth muscle layers; inner longitudinal, middle circular and outer longitudinal. The ureter is surrounded by adipose tissue and blood vessels.




The bladder, like the ureter, is lined by transitional epithelium. Beneath the epithelium and its underlying connective tissue, the wall of the bladder contains smooth muscle arranged in inner longitudinal, middle circular, and outer longitudinal layers.


Squamous cell carcinoma of bladder:

At low power on this slide, the mucosa is the purple-stained tissue lining the folds of the bladder wall. The tumour cells arise from the epithelium and infiltrate in sheets and nests into the stromal tissue. Well-circumscribed nests of deeply staining tumour cells can be identified within and below the epithelium along the inferior portion of the slide. Keratinized tumour cells, at low power, are polygonal, have well defined cell borders, amphophilic to eosinophilic “glassy” cytoplasm and pleomorphic nuclei with prominent nucleoli.



Transitional cell carcinoma of bladder:

Tumour cells in transitional cell carcinoma of the bladder are arranged in a papillary pattern, which can be seen throughout this slide. Multiple layers of atypical transitional epithelium line delicate fibrovascular cores. At high power, the tumour cells have clearly defined borders, small nuclei and abundant cytoplasm.