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Testosterone Hormone Feedback Mechanisms

APBIO-BFWGG@

Testosterone is a steroid hormone produced by all vertebrate animals and, in humans and other mammals, it is secreted in large amounts by the testes of males and, to a much lesser extent, the ovaries of females.

In adult males, testosterone plays a key role in the development of reproductive organs, and it promotes the secondary sexual characteristics of body and facial hair, increased muscle and bone mass, and a deep voice. Testosterone, like all hormones, works via long distance signaling and is regulated by other hormones as illustrated below:

Figure 1: Testosterone regulation by cooperation between the hypothalamus, pituitary, and testicular endocrine glands. The major regulatory hormones involved are luteinizing hormone (LH), follicle-stimulating hormone (FSH) and gonadotropin-releasing hormone (GnRH). "Testosterone." Wikipedia. Wikimedia Foundation, 15 Aug. 2010. Web. 11 July 2016.

When testosterone levels are low, gonadotropin-releasing hormone (GnRH) is released by the hypothalamus, which in turn stimulates the pituitary gland to release FSH and LH. FSH and LH then stimulate the testes to produce testosterone.

Which of the following describes how homeostasis is achieved when testosterone levels begin to rise?

A

Increasing levels of testosterone act on the hypothalamus and pituitary through a negative feedback loop to inhibit the release of GnRH and FSH/LH, respectively. This results in a decrease in testosterone production in the testes.

B

Increasing levels of testosterone act on the hypothalamus and pituitary through a positive feedback loop to inhibit the release of GnRH and FSH/LH, respectively. This results in a decrease in testosterone production in the testes.

C

Increasing levels of testosterone shut down the hypothalamus and pituitary through a negative feedback loop, which results in a decrease in testosterone.

D

Increasing levels of testosterone shut down the hypothalamus and pituitary through a positive feedback loop, which results in a decrease in testosterone.