ENDOCRINE SYSTEM
ENDOCRINE
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Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
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When epinephrine binds to cardiac (heart) muscle cells, it speeds their contraction. When it binds to muscle cells of the small intestine, it inhibits their contraction. Which of the following best accounts for the fact that the same hormone can have different effects on muscle cells?
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Cardiac cells have more receptors for epinephrine than do intestinal cells.
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Epinephrine circulates to the heart first and thus is in higher concentration around cardiac cells.
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The two types of muscle cells have different signal transduction pathways for epinephrine and thus have different cellular responses.
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Cardiac muscle is stronger than intestinal muscle and thus has a stronger response toepinephrine.
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Explanation:
Detailed explanation-1: -Contraction of heart muscle is regulated by binding of Ca2+ ions to troponin in the muscle thin filaments, causing a change in filament structure that allows myosin binding and force generation.
Detailed explanation-2: -The calcium that enters the heart cell through the calcium ion channel activates the ryanodine receptor to release enough calcium from the sarcoplasmic reticulum to initiate heart muscle contraction. This is done by binding to another structure, named troponin, inside the heart muscle cell.
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