Puberty Endocrine Events - Anatomy & Physiology

()Map REPRODUCTIVE SYSTEM (Map) PUBERTY

Hypothalamic Neurone Release of GnRH

• Hypothalamic development occurs gradually with growth of the animal.

Female

• The Hypothalamus contains a tonic GnRH centre and a preovulatory GnRH 'surge' centre.
• Before puberty can occur, full neural activity of the surge centre must be achieved.
• GnRH neurons must fire frequently and release large quantities of GnRH in order to cause the pre-ovulatory LH surge.
• The pre-ovulatory LH surge is a series of rapid, high amplitude pulses.
• Inability of the surge centre to function will result in failure to ovulate.
• In addition to the surge centre in the female, at puberty the tonic centre must also reach a functional state.
• The tonic centre regulates the tonic frequency of GnRH pulses.

Male

• Does not develop a surge centre.
• The feedback system after puberty is a simple negative feedback loop.
• The negative feedback effect on GnRH is mainly due to some testosterone and mostly due to oestradiol because most testosterone is converted to oestradiol within the brain by aromatization.
• GnRH neurons become increasingly less sensitive to the negative feedback of testosterone and oestradiol as puberty approaches.
• Larger and larger quantities of testosterone and oestradiol are needed to inhibit the GnRH neurons.
• Thus, there is decreased sensitivity to the negative feedback of testosterone/oestrodiol.
• Therefore, the hypothalamus can produce increasing amounts of GnRH.
• Thus, more LH and FSH are produced until puberty is reached.