What is the gonadal axis?
The gonadal axis involves a complex interaction between the hypothalamus, pituitary gland and the gonads. The system works together to regulate development, reproduction, ageing and many other body processes. Its regulation relies upon a number of complex negative feedback loops which when lost, result in disease.
How the male gonadal axis works
1. The hypothalamus secretes GnRH.
2. GnRH travels down to the anterior pituitary gland.
3. It binds to receptors on the pituitary gland.
4. This causes release of LH (luteinizing hormone) and FSH (follicle stimulating hormone).
5. LH and FSH travel in the blood stream to the testicles.
6. LH stimulates leydig cells in the testicles to produce testosterone
- Testosterone is required for spermatogenesis and many other important biological processes
7. FSH stimulates sertoli cells to produce androgen binding globulin (ABG) and inhibin
- ABG is a protein which binds to testosterone and keeps it within the seminiferous tubules
- Inhibin helps support spermatogenesis and inhibits production of FSH, LH and GnRH
8. ↑ levels of testosterone and inhibin cause negative feedback on the pituitary and hypothalamus.
9. This results in decreased production of LH and FSH.
10. As a result production of testosterone and inhibin is also decreased.
How the female gonadal axis works
1. The hypothalamus secretes GnRH.
2. GnRH travels down to the anterior pituitary gland.
3. It binds to receptors on the pituitary gland.
4. This causes release of LH (luteinizing hormone) and FSH (follicle stimulating hormone).
5. LH and FSH travel in the blood stream to the ovaries.
6. When LH and FSH bind to the ovaries they stimulate production of oestrogen and inhibin
- Oestrogen helps regulate the menstrual cycle and is essential in many body processes
- Inhibin causes inhibition of activin which is usually responsible for stimulating GnRH production
7. Increasing levels of oestrogen and inhibin cause negative feedback on the pituitary and hypothalamus.
8. This leads to decreased production of GnRH, LH and FSH.
9. This in turn results in decreased production of oestrogen and inhibin.
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