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32. A higher power view of the outer medulla reveals the several different tubule types found in this location: proximal tubules (here called the thick descending limb of the loop of Henle), thin limbs of the loop of Henle (one cannot tell whether it's ascending or descending), distal tubules (aka thick ascending limb), and collecting ducts. Blood engorged capillaries may also be seen. Proximal tubules are distinguished by their collapsed lumina, dark, sometimes 'grainy' staining, and a brush border. Collecting ducts are best distinguished by their prominent cell borders. Thin limbs are lined by a simple squamous epithelium. Distal tubules show lighter staining, no brush border, open lumina, but no prominent cell boundaries. In this section from the outer medulla, also note the very sparse interstitial tissue (stained green) between the tubular elements.
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