Encyclopedia of Pathology

Living Edition
| Editors: J.H.J.M. van Krieken

Kidney, Normal Histology

  • Anna Caliò
  • Diego Segala
  • Guido MartignoniEmail author
Living reference work entry
DOI: https://doi.org/10.1007/978-3-319-28845-1_4836-1


The kidneys are paired, bean-shaped organs located in the retroperitoneum.


Kidneys filter blood in a three-step process: (1) the nephrons filter blood through the capillary network in the glomerulus (glomerular filtration); (2) the filtrate is collected in the renal tubules (tubular reabsorption); and (3) additional solutes and wastes are secreted into the kidney tubules (tubular secretion).

Juxtaglomerular cells are specialized cells located within the afferent arterioles of the kidney which produce renin to control blood pressure.

Size and Weight

Adult kidneys average 150 g and are approximately 12 cm long, 6 cm wide, and 3 cm thick.


Each kidney consists of an outer cortex and an inner medulla. The medulla has roughly 12 pyramids, with their bases at the corticomedullary junction. A medullary pyramid and its overlying cortex constitute a renal lobe.


The nephron is the functional unit of the kidney and includes the glomerulus and its tubule, the latter terminating at a common collecting system. The glomerulus is a specialized network of capillaries covered by epithelial cells named podocytes and supported by modified smooth muscle cells called mesangial cells (Fig. 1). As it enters the glomerulus, the afferent arteriole branches into capillaries, which form the convoluted glomerular tuft and eventually coalesce into the efferent arteriole that exits the glomerulus. The Bowman space lies between the podocytes and the epithelial cells that line the Bowman capsule. The major segments of the tubule that arise from each glomerulus are the proximal tubule, loop of Henle, and distal tubule, which empties into the collecting duct. At the origin of the proximal tubule from the glomerulus, the flat epithelium of the Bowman capsule abruptly transforms into tall columnar cells of the proximal tubule, which have numerous tall microvilli forming a brush border. The initial segment is very tortuous and is called the proximal convoluted tubule. As it descends into the medulla, the proximal tubule straightens into the thick descending limb of the loop of Henle. Further into the medulla, the thick descending limb thins into the thin limb of the loop of Henle, which eventually loops back toward the cortex. Approaching the cortex, the thin limb becomes the thick ascending limb. This abuts the glomerulus from which it arose, contributes to that glomerulus’ juxtaglomerular apparatus, and then becomes the distal convoluted tubule. Several distal tubules unite to form a collecting duct, which ultimately empties into the ducts of Bellini, which discharge urine through the papillae into the calyces. The juxtaglomerular apparatus is at the hilus of the glomerulus and consists of (I) macula densa, a region of the thick ascending limb of the loop of Henle with closely packed nuclei; (II) extraglomerular mesangial cells, between the macula densa and the hilar arterioles; and (III) terminal afferent arteriole and proximal efferent arteriole. The wall of the afferent arteriole contains characteristic granular cells involved in the synthesis and secretion of renin and angiotensin.


CD10 and CD13 stain the proximal tubules, whereas calcium-binding proteins such as parvalbumin are usually positive in the distal nephron. GATA3, nuclear marker commonly used for the urothelial differentiation, is expressed both in the urothelium of renal pelvis, the podocytes, and the distal nephron. PAX8 stains the epithelial cells of the proximal and distal renal tubules, loops of Henle, collecting ducts, and the parietal epithelial cells of Bowman’s capsule (Martignoni et al. 2004; Tong et al. 2009).
Fig. 1

Normal histology of the renal parenchyma including cortex and medulla. In the insert, a high magnification of the glomerulus and the closer distal and proximal tubules

References and Further Reading

  1. Martignoni, G., Pea, M., Brunelli, M., et al. (2004). CD10 is expressed in a subset of chromophobe renal cell carcinomas. Modern Pathology, 17, 1455–1463.CrossRefGoogle Scholar
  2. Tong, G. X., Yu, W. M., Beaubier, N. T., et al. (2009). Expression of PAX8 in normal and neoplastic renal tissues: An immunohistochemical study. Modern Pathology, 22, 1218–1227.CrossRefGoogle Scholar

Copyright information

© Springer Nature Switzerland AG 2019

Authors and Affiliations

  1. 1.Department of Diagnostic and Public Health, Section of PathologyUniversity of VeronaVeronaItaly
  2. 2.Department of PathologyPederzoli HospitalPeschiera del GardaItaly