Figure 1. Longitudinally sectioned left and cross-sectioned right kidneys.
Figure 2. Demarcated regions of the kidney: cortex, outer stripe of the outer medulla (OSOM), inner stripe of the outer medulla (ISOM), inner medulla, papilla, and renal pelvis.
One of the most heterogeneous tissues in the body, the kidney has a wide variety of cell types. For the most part, renal tubules and/or ducts comprise most of the renal parenchyma and are lined by specialized epithelial cells. Renal interstitial tissue is sparse in the cortex and gradually increases toward the papilla. The distribution of the renal vasculature is uniquely suited to supply more blood to the energy-active cortex.
Each area of the kidney contains defined segments of the nephron, the functional unit of the kidney, and portions of the collecting duct system. It is imperative for pathologists to understand the relationships among the anatomic locations of the various segments of the nephron or collecting duct system since some chemicals have a selective affinity for a particular nephron or duct segment.
Figure 3. Schematic of the anatomic locations of the various nephron and collecting duct segments within the kidney. Image by David Sabio.
Figure 4. Histologic appearance of cortical renal tubules and glomeruli in a rat.
Figure 5. Tubule and glomerular basement membranes and proximal convoluted tubule brush borders outlined by PAS staining.
Figure 6. The fornices appear as folds within the upper portion of the renal pelves.
Figure 7. The papilla and surrounding renal pelvis with the adjacent renal hilar area containing the large renal artery and vein. The urothelium-lined opening to the ureter may also be seen.
Figure 8. A low-power image of diffuse tubule autolysis mimicking necrosis.
The kidney undergoes autolysis rapidly, and kidneys from moribund animals or animals dying on test have histologic changes associated with autolysis. Even specimens immersion fixed at the time of sacrifice may contain subtle to large areas of autolysis within the kidney mimicking degeneration and necrosis ( Figure 8 ). Autolysis must be differentiated from lesions such as tubule epithelial vacuolation, degeneration, or acute necrosis. At times this differentiation is difficult even for the seasoned pathologist. Histologic changes associated with autolysis include varying degrees of focal, zonal, or diffuse pale-staining tissue, loss of cytoplasmic and nuclear detail (rarefaction or “ghost-like” cells), retraction of tubule epithelial cells from basement membranes, and tubule vacuolation ( Figure 9 , Figure 10 ). Desquamation of tubule epithelial cells has been reported with autolysis and, therefore, is not always a reliable indicator of tubule cell necrosis.
Figure 9. Consistent histologic features of autolysis are characterized by loss of cytoplasmic and nuclear detail (rarefaction) and retraction of tubule epithelial cells from basement membranes.
Figure 10. Autolytic vacuolation in a male rat that died on test.
Additional artifacts such as mineralization in the outer cortex may be observed and should not be confused with real mineralization ( Figure 11 ).
Figure 11. Artifactual mineralization represented by irregular foci of basophilia in the outer cortex of a male rat.
For more detailed information on the anatomy and physiology of the kidney, see Sands JM, Verlander JW. 2005. Anatomy and physiology of the kidneys. In: Toxicology of the Kidney, 3rd ed (Tarloff JB, Lash LH, eds). CRC Press, Boca Raton, FL, 3-56.
Sands JM, Verlander JW. 2005. Anatomy and physiology of the kidneys. In: Toxicology of the Kidney, 3rd ed (Tarloff JB, Lash LH, eds). CRC Press, Boca Raton, FL, 3-56. Abstract: http://www.crcnetbase.com/ISBN/9780203646991
Web page last updated on: October 23, 2014