D3.1.13 Control of the developmental changes of puberty (HL) Notes

GnRH Triggers the Hormonal Cascade of Puberty

1. Puberty begins when the hypothalamus increases the secretion of gonadotropin-releasing hormone (GnRH).
2. This peptide hormone is released in pulses, which is critical for its effectiveness.
3. GnRH acts on the pituitary gland, triggering the release of luteinizing hormone (LH) and follicle-stimulating hormone (FSH).
4. Together, these hormones stimulate the gonads to produce sex hormones, which drive the physical and physiological changes of puberty.

LH and FSH Drive Sex Hormone Production

1. Luteinizing Hormone (LH):
   1. In males: LH stimulates the testes to produce testosterone, which drives changes like increased muscle mass and deepening of the voice.
   2. In females: LH triggers the ovaries to produce oestradiol and supports ovulation during the menstrual cycle.
2. Follicle-Stimulating Hormone (FSH):
   1. In males: FSH promotes sperm production in the testes.
   2. In females: FSH supports the growth and maturation of ovarian follicles, which produce eggs.

Sex Hormones and Their Effects on Puberty

1. Testosterone in males:
   1. Stimulates the growth of the penis and testes.
   2. Drives the development of secondary sexual characteristics like facial hair and a deeper voice.
2. Oestradiol in females:
   1. Promotes breast development and the menstrual cycle.
   2. Causes fat redistribution and widening of the hips.

The Role of Feedback Mechanisms

1. Hormonal regulation during puberty relies on feedback loops to maintain balance:
   1. Negative Feedback: High levels of testosterone or oestradiol inhibit GnRH, LH, and FSH production to prevent overproduction.
   2. Positive Feedback: In females, high oestradiol levels temporarily stimulate an LH surge, leading to ovulation.

Why Does Puberty Start?

1. The precise trigger for puberty remains unclear, but key factors include:
   1. Genetic Factors: Genes influence when the hypothalamus begins increasing GnRH secretion.
   2. Nutritional Status: Adequate body fat and hormones like leptin may signal readiness for puberty.
   3. Environmental Factors: Stress, physical activity, and chemical exposure can affect timing.

Reflection

1. Puberty is a remarkable period of transformation, driven by the precise coordination of hormones.
2. Understanding the roles of GnRH, LH, FSH, and steroid sex hormones provides insight into how the body prepares for reproductive maturity.