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SUMMARY Branches of tortuous arteries in the adventitia of the minor calyces supply blood to the renal papilla. The papilla therefore receives blood from both the vasa recta and the calyx. In certain pathological conditions this dual blood supply is of importance. It probably accounts for the preservation of the papilla and adjacent medulla in cases of acute tubular necrosis. When the calycine vessels are occluded, any interference with the blood supply through the vasa recta, such as occurs during peripheral circulatory failure, is liable to lead to ischemic necrosis of the renal papilla. [ABSTRACT FROM AUTHOR]

A letter to the editor is presented in response to the article on teaching ethics in the May 26, 2007 issue.

The fiber distribution and ultrastructure in the plantaris longus pressure-bearing tendon of the bullfrog were investigated. The tension region of the tendon showed a predominant parallel distribution of collagen fibers, but three main zones with different crimp parameters were identified with the use of the polarizing microscope. The compression region showed collagen fibers with aspects of disaggregation and were composed of disperse and undulating fibrils. These collagen fibers establish a three-dimensional network but showed a preferential distribution in planes disposed perpendicularly to the tendon's main axis. It is assumed that the convoluted and disaggregated collagen fibers must be distended before exerting any reinforcement on the tissue and that this only occurs after a great deformation of the tendon. Groups of 5-6 fibrils not associated in fibers are also dispersed in the compression region. The tissue is assumed to have a highly viscous fluid nature allowing for the deformation needed for collagen fibrils to reinforce the tendon structure. The convoluted and crimped structure of collagen fibers would be especially useful when the tendon is submitted to the sudden and strong mechanical loading expected to occur during jumping and to provide the tendon with the capacity of great functional deformability necessary for the high amplitude of feet movements attained on jumping and swimming.