試題詳解

40. Oxytocin is a hormone involved in various physiological processes including uterine contractions during childbirth and milk ejection during lactation. Which of the following best describes the feedback mechanism that regulates oxytocin release during childbirth?
(A) Oxytocin release is regulated by a negative feedback loop; as oxytocin levels rise, they inhibit the release of prostaglandins, which further reduces uterine contractions.
(B) Oxytocin release is controlled by a negative feedback mechanism: increased oxytocin levels stimulate the release of corticotropin-releasing hormone (CRH), which further suppresses oxytocin secretion.
(C) Oxytocin secretion is controlled by a negative feedback loop: high levels of oxytocin directly inhibit neurons in the hypothalamus, which is responsible for its synthesis and release.
(D) Oxytocin release is independent of any feedback mechanism and is determined solely by hormonal signals from the placenta.
(E) Oxytocin release during childbirth is a classic example of a positive feedback loop; uterine contractions stimulate the release of oxytocin, which in turn intensifies contractions, leading to a self-reinforcing cycle until childbirth is complete. After birth, the stimulus (cervical stretching) is removed, and oxytocin levels decline.