6 Questions
What is the primary source of gonadotropin-releasing hormone (GnRH) synthesis and release?
Anterior hypothalamus
During which period does the HPG axis undergo significant activation?
Three periods: fetal life, mini-puberty, and after childhood
What is the primary role of GnRH-secreting neurons during fetal life?
Development of reproductive organs
What causes the suppression of the HPG axis in early infancy?
Placental estrogens
At what age does the 'mini-puberty' period occur?
From the first week of life to 6 to 9 months of age
What is the direction of migration of GnRH-secreting neurons during fetal life?
From the medial olfactory pit to the hypothalamus
Study Notes
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.
This quiz covers the process of puberty, including the activation of the hypothalamic-pituitary-gonadal axis, and the role of various hormones in gamete production and gonadal steroid release. Learn about the three activation periods of the HPG axis and how it affects human development.
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