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Chapter 12. Digestive System

The mutation responsible for cystic fibrosis produces a defect in Cl transport across epithelial cells, which also reduces the transmembrane movements of cations such as Na+. This results in the production of saliva containing a higher than normal concentration of NaCl. Which of the following type of cells in salivary glands is most likely affected in this case?

A. Intercalated duct cells

B. Interlobular duct cells

C. Mucous secretory cells

D. Serous secretory cells

E. Striated duct cells

The answer is E: The striated duct cells actively resorb NaCl, which creates hypotonic saliva and helps recover water to the circulatory system. The saliva of individuals with cystic fibrosis is "saltier" than normal. Several screening tests based on measuring the NaCl concentration of epithelial secretions have been developed to detect cystic fibrosis in newborns. Testing sweat is a common method, as are genetic tests. Parents often identify infants with the disease because the infant "tastes salty."

A 48-year-old man is seen by his physician because he is having difficulty swallowing. An endoscopic examination of the esophagus shows abnormal growths beginning immediately below the pharynx and continuing down more than two-thirds of the length of the organ. Biopsy specimens are obtained at two sites, one from the top and one from the bottom of the esophagus, and are sent to the histopathology laboratory. The pathologist is able to verify the locations of the biopsy specimens by observation of which tissue layer?

A. Adventitia

B. Mucosa

C. Muscularis externa

D. Submucosa

The answer is C: The muscularis externa of the esophagus contains only skeletal muscle in the upper third of the tube and only smooth muscle in the lower third, so the biopsy specimen containing skeletal muscle must be the one taken from the upper portion and the specimen containing only smooth muscle in the muscularis externa must be taken from the inferior portion.

A 23-year-old man has been diagnosed with vitamin B12 deficiency and begins taking oral supplements containing vitamin B12. The patient's symptoms, however, do not improve, and serum analysis indicates that he is not absorbing the supplement. The physician suspects that the patient may be suffering from an autoimmune condition and orders laboratory studies. The studies show the presence of antibodies in the serum that are reactive against gastric cells. Which is the most likely target of these autoantibodies?


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