Mechanism of underlying elevated sodium chloride levels in the sweat of patients with cystic fibrosis (CF). Sweat ducts (Panel A) in patients with CF differ from those in people without the disease in the ability to reabsorb chloride before the emergence of sweat on the surface of the skin. A major pathway for Cl– absorption is through CFTR, situated within luminal plasma membranes of cells lining the duct (ie, on the apical, or mucosal, cell surface) (Panel B). Diminished chloride reabsorption in the setting of continued sodium uptake leads to an elevated transepithelial potential difference across the wall of the sweat duct, and the lumen becomes more negatively charged because of a failure to reabsorb chloride (Panel C). The result is that total sodium chloride flux is markedly decreased, leading to increased salt content. The thickness of the arrows corresponds to the degree of movement of ions. (Used with permission from Rowe SM, Miller S, Sorscher EJ. Cystic fibrosis. N Engl J Med 2005;352[19]:1992-2001.) Source: Cystic Fibrosis, Pharmacotherapy: A Pathophysiologic Approach, 10e Citation: DiPiro JT, Talbert RL, Yee GC, Matzke GR, Wells BG, Posey L. Pharmacotherapy: A Pathophysiologic Approach, 10e; 2017 Available at: http://accesspharmacy.mhmedical.com/DownloadImage.aspx?image=/data/books/1861/dipipharm10_ch29_f001.png&sec=134126899&BookID=1861&ChapterSecID=134126883&imagename= Accessed: December 25, 2017 Copyright © 2017 McGraw-Hill Education. All rights reserved