Puberty and the HPG Axis

Puberty and HPG Axis

• Puberty begins with the activation of the hypothalamic-pituitary-gonadal (HPG) axis.
• The anterior hypothalamus synthesizes and releases gonadotropin-releasing hormone (GnRH), which stimulates the anterior pituitary to release gonadotropins, luteinizing hormone (LH), and follicle-stimulating hormone (FSH).
• LH and FSH stimulate gonadal steroid release and gamete production.

HPG Axis Activation Periods

• The HPG axis has three activation periods: during fetal life, a "mini-puberty" from the first week of life to 6 to 9 months of age, and finally, after childhood, which is the period commonly defined as puberty.

Development of GnRH-Secreting Neurons

• GnRH-secreting neurons originate from the epithelium of the medial olfactory pit at about 40 days' gestation.
• These neurons migrate along nerve fibers to the hypothalamus.

HPG Axis Activation During Fetal Life

• HPG axis activation during fetal life allows for reproductive organ development.
• It is also thought to be responsible for central programming, which leads to sex dimorphic body composition later in life.

Suppression of HPG Axis

• Placental estrogens increase at 37 to 40 weeks' gestation and suppress the HPG axis in early infancy.
• After birth, gonadotropin levels initially decline, and then increase again at 6 to 10 days after birth.