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Three‐dimensional reconstructions of rat renal inner medulla suggest two anatomically separated countercurrent mechanisms for urine concentration
Author(s) -
Pannabecker Thomas Lloyd,
Dantzler William H,
Layton Anita T,
Layton Harold E
Publication year - 2008
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.22.1_supplement.1216.3
Subject(s) - vasa recta , countercurrent exchange , loop of henle , biophysics , chemistry , anatomy , nephron , medullary cavity , crystallography , biology , biochemistry , renal function
From 0 to 3.5 mm below inner medullary (IM) border, collecting duct (CD) clusters form an organizing motif with descending thin limbs (DTLs) and descending vasa recta (DVR) lying outside CD clusters. Ascending thin limbs (ATLs) and ascending vasa recta (AVR) are uniformly distributed inside and outside CD clusters. This arrangement suggests two functionally distinct countercurrent systems (CCSs) exist: one inside and one outside CD clusters. CCS inside each cluster delivers NaCl from prebends and corresponding part of ATLs, and urea and water from CDs, to interstitial nodal sites bounded by CDs, AVR, ATLs, and interstitial cells. This CCS (ascending AVR and ATL flows and descending CD flows) produces isolated sites of high osmolality that withdraw water from CDs. This CCS has three subsystems related to distance from IM border: 1) loops with no AQP1 turning within CD clusters in first 1 mm; 2) loops lacking AQP1 for last 60% turning within CD clusters in next 2–2.5 mm; 3) loops lacking AQP1 for last 60% turning next to remaining CDs in final 1.5–2 mm. Last 0.5 mm of this CCS has loops with narrow bends and loops with broad transverse bends. Transverse bends permit NaCl point delivery optimal for generating high osmolality at papilla tip. CCS of loops and vessels outside CD cluster may be shielded from high urea concentrations inside cluster and ensure NaCl and urea absorption from ATLs. (NIH DK‐16294, DK‐42091; NSF DMS‐0715021)