Questions: Which of the following hormones is regulated by a positive feedback mechanism? TRH oxytocin TSH thyroxine

The answer is the second one (B): oxytocin.

Explanation for each option:

A. TRH (Thyrotropin-releasing hormone) - This hormone is regulated by a negative feedback mechanism. It is involved in the regulation of the thyroid gland, where increased levels of thyroid hormones inhibit the release of TRH.

B. Oxytocin - This hormone is regulated by a positive feedback mechanism. During childbirth, the release of oxytocin causes uterine contractions, which in turn stimulate more oxytocin release, enhancing the contractions until delivery occurs.

C. TSH (Thyroid-stimulating hormone) - Like TRH, TSH is also regulated by a negative feedback mechanism. High levels of thyroid hormones inhibit the release of TSH.

D. Thyroxine - This hormone is part of the thyroid hormone group and is regulated by a negative feedback mechanism. Increased levels of thyroxine inhibit the release of TRH and TSH.

In summary, oxytocin is the hormone regulated by a positive feedback mechanism.