Anatomical features in the kidney involved in water conservation through urine concentration in dromedaries (Camelus dromedarius)

Abstract

The aim of this study was to report some of the morphological characteristics of the kidney involved in urine concentration and hence water conservation in the dromedaries. A total of 20 fresh kidneys of 10 apparently healthy camels were used in this study. The architecture of the renal pelvis was revealed by dissection and polyvinyl chloride corrosion casts. Samples were also processed for histology and for enzyme histochemistry. The camel kidney is bean shaped, smooth, multilobar, unipapillary, in which the fusion of renal papillae is complete forming a common renal papilla or crest, which channel urine into a central renal pelvis. It is more or less similar to equine, caprine, ovine and canine kidney. Under certain anatomical requisites the renal pelvis is known to play a role in urine concentration through recycling of urea to increase the medullary osmotic concentration which favors the counter-current mechanism. One of these requisites is an elaborate renal pelvis which is closely associated with the renal medulla. The renal pelvis of the camel has a main crescentic cavity following the long axis and curvature of the kidney. A thick extensive renal crest projects into the cavity of the pelvis. The thick renal crest contains large numbers of long loops of Henle and vasa recta which are important for urine concentration. The renal crest is formed by convergence of the medullary pyramids before it projects into the cavity of the renal pelvis. The crescentic main cavity of the pelvis forms 20–24 three dimensional radiating collateral recesses which contain the medullary pyramids. This close association of the renal pelvis and medulla provide a large surface area for the recycling of urea and hence urine concentration. This large pelvic-medullary interface is lined by simple low cuboidal epithelium which enhances the recycling of urea and water from the pelvic urine into the medulla and directly contributes to urine concentration. The rest of the wall of the renal pelvis and its recesses facing away from the renal crest and medullary pyramids is lined by impermeable transitional epithelium. Another feature is the intense activity of alkaline phosphatase demonstrated in the proximal convoluted tubules which indicates increased membrane transport. It is concluded that the kidney in dromedaries has the anatomical and histochemical requisites for the production of concentrated urine. These requisites enable the kidney to adequately contribute to the ability of the camel to conserve water and withstand the aridity of its habitat.