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Chapter 2. Overview of Cellular Physiology in Medical Physiology

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A student housed his new pet dog in his yard while he went off to school. Upon return, the dog was drooling and vomiting. Upon tending to the dog, the student noticed additional, more severe symptoms that included dilated pupils and an irregular and very fast heartbeat. Looking around the yard, the student noticed that a foxglove plant had been damaged. He suspected that the dog had ingested the foxglove and received a relatively high dose of the cardiac glycoside digitalin that can directly affect the electrogenic Na, K ATPase. Which of the below best describes how the Na, K ATPase functions?

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A. It uses the energy in ATP to extrude 3 Na+ out of the cell in exchange for taking two K+ into the cell.

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B. It uses the energy in ATP to extrude 3 K+ out of the cell in exchange for taking two Na+ into the cell.

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C. It uses the energy in moving Na+ into the cell or K+ outside the cell to make ATP.

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D. It uses the energy in moving Na+ outside of the cell or K+ inside the cell to make ATP.

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The correct answer is A. The foxglove plant, and more specifically the inhibitory cardiac glycoside contained in the foxglove that interrupts Na, K ATPase activity, has been used for over two centuries to manage certain heart malfunctions. However, excessive doses of these cardiac glycosides such as can occur after uncontrolled eating of the plant can cause significant pathology. Under normal circumstances, Na, K ATPase moves 3 Na+ out of the cell for every two K+ that move in, ruling out B. While the Na, K ATPase is electrogenic, Na+ and K+ both move “up” their electrochemical gradients and require energy for this movement, ruling out C and D.

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Students in an introductory laboratory class are able to isolate apical and basolateral membranes from undifferentiated and differentiated gut epithelial cells. Following isolation, the students can categorize the protein, lipid and carbohydrate makeup of each batch of isolated membranes. Results from these experiments help them to draw which of the following conclusions about cell membranes?

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A. Cell membranes contain relatively few protein molecules.

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B. Cell membranes contain mostly carbohydrate molecules.

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C. Cell membranes are freely permeable to electrolytes but not to proteins.

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D. Cell membranes have variable protein and lipid contents depending on their location in the cell.

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