Sweat glands in cystic fibrosis
**Core Concept**
Cystic fibrosis is a genetic disorder characterized by mutations in the CFTR gene, leading to abnormal chloride ion transport across epithelial membranes. This impairment affects various organs, including the respiratory, gastrointestinal, and reproductive systems. In the context of sweat glands, the defective ion transport results in abnormal electrolyte balance and increased sweat chloride levels.
**Why the Correct Answer is Right**
The defective CFTR protein in cystic fibrosis impairs the chloride ion channel function in sweat glands. Normally, chloride ions are secreted into the sweat, and sodium ions are reabsorbed, resulting in a low chloride concentration in sweat. However, in cystic fibrosis, the reduced chloride secretion and increased sodium reabsorption lead to a higher concentration of chloride ions in the sweat. This is why sweat chloride tests are commonly used as a diagnostic tool for cystic fibrosis.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not address the underlying pathophysiology of sweat gland function in cystic fibrosis. While it may be a related concept, it does not directly explain the relationship between CFTR mutations and sweat chloride levels.
**Option B:** This option is incorrect because it is not relevant to the specific context of sweat glands in cystic fibrosis. The relationship between CFTR mutations and sweat chloride levels is a distinct phenomenon that is not directly related to other aspects of cystic fibrosis pathology.
**Option C:** This option is incorrect because it does not accurately describe the primary mechanism underlying sweat gland dysfunction in cystic fibrosis. While CFTR mutations do affect epithelial ion transport, the specific impact on sweat glands and chloride levels is a distinct aspect of the disease.
**Clinical Pearl / High-Yield Fact**
A key clinical correlation to remember is that elevated sweat chloride levels in a newborn or infant are a critical diagnostic criterion for cystic fibrosis. This is because the disease is typically diagnosed in early childhood, and sweat chloride tests are a non-invasive and reliable method for identifying affected individuals.
**Correct Answer:** D.