Vasa recta (kidney)

Microanatomy On a histological slide, the straight arterioles can be distinguished from the tubules of the loop of Henle by the presence of blood. ==Function==

Each straight arteriole has a hairpin turn in the medulla and carries blood at a very slow rate – two factors crucial in the maintenance of countercurrent exchange that prevent washout of the concentration gradients established in the renal medulla. The maintenance of this concentration gradient is one of the components responsible for the kidney's ability to produce concentrated urine. On the descending portion of the vasa recta, sodium, chloride and urea are reabsorbed into the blood, while water is secreted. On the ascending portion, sodium chloride and urea are secreted into the interstitium, while water is reabsorbed. ==Clinical significance==

The slow blood flow in the straight arterioles makes them a likely location of thrombosis from thrombophilia, or tissue loss due to red blood cell sickling in sickle cell disease. Ischemia that results may lead to renal papillary necrosis. == Nomenclature ==

According to Terminologia Anatomica, the term "vasa recta renis" is an alternate name for "arteriolae rectae renis", and a separate term, venulae rectae renis, is used to identify the venous portion. However, other sources consider "vasa recta" to refer to both the arterial and venous portions. The term vasa recta is also used for the intestines – vasa recta (intestines) (in the ileum and jejunum) ==References==