DSSSB 6 September 2024
Applied Physiology
Medium
All of the following processes in the body are controlled by a positive feedback mechanism, EXCEPT:
Appeared in: DSSSB 6 September 2024
Explanation
- Thyroid hormone secretion is the correct answer because it operates on a negative feedback loop, which is the opposite of a positive feedback mechanism.
- The hypothalamic-pituitary-thyroid (HPT) axis regulates thyroid hormone levels.
- When thyroid hormone (T3 and T4) levels are high, they inhibit the release of Thyrotropin-Releasing Hormone (TRH) from the hypothalamus and Thyroid-Stimulating Hormone (TSH) from the pituitary.
- This inhibition reduces the production and release of thyroid hormones, thereby maintaining homeostasis.
- This counter-regulatory action is the defining characteristic of a negative feedback system.
Why Other Options Were Wrong
- Option A: Milk production (lactogenesis) is a classic example of a positive feedback loop.
- Option C: Childbirth (parturition) is a primary example of a physiological process driven by a positive feedback loop involving oxytocin and uterine contractions.
- Option D: The milk ejection or 'let-down' reflex is a neuro-hormonal reflex that operates via positive feedback, stimulated by suckling and mediated by oxytocin.
Related Visual
Clinical Relevance
- Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Physiological Feedback Mechanisms (Positive vs. Negative) as background academic context rather than a clinical decision trigger.
- Understanding feedback loops is fundamental to nursing, especially in endocrinology. It helps in assessing, diagnosing, and managing hormonal imbalances.
- For example, in primary hypothyroidism, the thyroid gland fails, leading to low T3/T4. The lack of negative feedback causes the pituitary to secrete high levels of TSH, which is a key diagnostic marker.
- Nurses manage labor by understanding the positive feedback of childbirth, sometimes administering synthetic oxytocin (Pitocin) to augment this natural process.
How to Approach the Question
- First, identify the keyword 'EXCEPT' in the question. This means you are looking for the option that does not fit the stated condition.
- The condition is 'controlled by a positive feedback mechanism'. Therefore, you need to find the process that is NOT controlled by positive feedback.
- Define positive feedback: a process that amplifies a change, moving the system further from its starting state.
- Evaluate each option: Childbirth, milk production, and milk ejection are all classic examples where a stimulus leads to a response that enhances the original stimulus.
- Evaluate the remaining option: Thyroid hormone secretion is controlled by the HPT axis, where high hormone levels inhibit further production. This is a stabilizing, or negative, feedback loop.
- Select the option that represents negative feedback, as it is the exception.
Concept Tested & Keywords
- Concept Tested: Physiological Feedback Mechanisms (Positive vs. Negative)
- Stem keywords: processes, body, controlled, positive feedback mechanism
- Lead-in keywords: EXCEPT
- Negative lead-in flag: The question asks for the process that is an EXCEPTION.
Question ID
QoNghA-74hQhdS6dxR4dsg
Reference Book
E6 Medicine Harrison 22e Part 2 pp. 890-892, 891-893
E6 Physiology Guyton 4SAE Part 3 p. 69-71
Practise the full DSSSB 6 September 2024
Attempt every question from this paper in a timed mock, then review the full solution for each one.
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