Structural Organization of the Kidney

2 FUNDAMENTAL ASPECTS OF RENAL PHYSIOLOGY 29.2.1 Structural Organization of the Kidney 

Molecular and Biochemical Toxicology, Fourth Edition, edited by Robert C. Smart and Ernest Hodgson Copyright 2008 John Wiley Sons, Inc. 

The renal medulla is the middle portion of the kidney and consists of the loops of Henle, vasa recta, and collecting ducts. Medullary blood flow (about 6% of total renal blood flow) is considerably lower than cortical flow. However, by virtue of its countercurrent arrangement between tubular and vascular components, the medulla may be exposed to high concentrations of toxicants within tubular and interstitial structures. 

The papilla is the smallest anatomical portion of the kidney. Papillary tissue consists primarily of terminal portions of the collecting duct system and the vasa recta. Papillary blood flow is low relative to cortex and medulla less than 1% of total renal blood flow reaches the papilla. However, tubular fluid is maximally concentrated and the volume of luminal fluid is maximally reduced within the papilla. Potential toxicants trapped in tubular lumens may attain extremely high concentrations within the papilla during the process of urinary concentration. High intraluminal concentrations of potential toxicants may result in diffusion of these chemicals into papillary tubular epithelial and/or interstitial cells, leading to cellular injury. 

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Fig. 2.9. Diagram of the structural organization of the kidney and its relationships to the zones of the kidney. CD, collecting duct CATT, connecting tubule DCT, distal convoluted tubule PT, proximal tubule TAL, thick ascending limb TL, thin limb of Henle s loop...

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