Thin Tubules (Thin Ascending Loop of Henle)

The straight portion of the proximal tubule (pars recta) enters a medullary ray and descends toward the medulla. Both parts of the proximal tubule are lined by cuboidal epithelial cells. The next tubular segment that the filtrate passes through is the thin tubule or thin loop of Henle which is mainly located in the medulla. Here the diameter of the tubule narrows markedly and the epithelium becomes simple squamous (see R-P, Fig. 20.17 & Pl. 73 or R-K-P, Fig. 19.17 & Pl. 73). The thin segment descends toward the apex of the pyramid. Before reaching the apex of the pyramid, however, it makes a hairpin turn and returns toward the cortex. Don’t confuse the thin segments of the tubules with the capillaries they associate with. Tubular epithelial cells are somewhat thicker, tubular diameter is somewhat greater, and the tubules do not contain RBCs. The next tubular segment is the distal thick tubule. The distal thick segment ascends through the medullary ray as the straight ascending segment. The straight ascending segment exits the medullary ray and returns to its corpuscle of origin. Try to identify each of these tubules by studying sections of the cortex and the medulla. Note the frequent appearance of arcuate artery and vein profiles along the boundary between the cortex and the medulla (B-67, H&E [2.5x-labeled, 10x, 20x, 40x-labeled]).

Thin Tubules Identifications

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-- AshleyLPistorio - 23 May 2007