Question
What occurs when a person stands from a supine position?
| A. |
Increase firing in baroreceptor afferents
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| B. |
Decrease firing in baroreceptor afferents
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| C. |
Vagal output to cardiac fibers increase
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| D. |
B and C Both
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Show Answer
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Correct Answer � B
Explanation
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When a person transitions from a supine position to standing, there are significant physiological changes in blood pressure and autonomic control:
Baroreceptor Reflex:
- Baroreceptors, located in the carotid sinuses and aortic arch, sense blood pressure changes.
- When a person stands, blood pools in the lower extremities due to gravity, leading to a temporary drop in blood pressure (orthostatic hypotension).
- This drop in blood pressure causes decreased firing of baroreceptor afferents (Option B). Baroreceptors sense less stretch in the vessel walls, resulting in decreased afferent signaling to the brain.
Vagal Output:
- In response to decreased baroreceptor activity, the brain reduces vagal output to the heart, which normally promotes parasympathetic (rest-and-digest) activity. This reduction in vagal output allows heart rate to increase as a compensatory mechanism to restore blood pressure.
- Therefore, vagal output decreases rather than increases.
