Cystic fibrosis sweat glands

Diagram of a sweat gland, showing paths taken by chloride ions (arrows) during secretion. In both normal and CF sweat glands in the dermis, chloride is present in secretions at a concentration of 105 mEq, equaling that in serum (“isotonic”). (Top) In the normal sweat gland, chloride is absorbed out of the sweat in a CFTR-dependent manner as the sweat travels from the gland to the skin surface. As a result, the chloride concentration in normal sweat is below that in serum (“hypotonic”), with <40 mEq considered normal and <20 mEq being typical. (Bottom) In the CF sweat gland, chloride absorption is hindered by defective CFTR function. As a result, sweat which reaches the skin surface has higher than normal chloride concentrations (>60 mEq).

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