Please answer the questions below are about the Hypothalamic Pituitary Gonadal A
ID: 141523 • Letter: P
Question
Please answer the questions below are about the Hypothalamic Pituitary Gonadal Axis (HPG Axis).
1. Generally, when a dog is neutered the veterinarian removes the testicles. How does this procedure alter the secretion of GnRH, LH and FSH?
2. The pituitary gland is found in the sella turcica of the sphenoid bone. It is attached to the brain by a thin stalk made up of blood vessels and nervous tissue. A traumatic brain injury can result in the stalk being torn from the brain. If this occurs how would testosterone secretion be affected?
3. If an athlete is injecting testosterone what happens to GnRH, LH and FSH secretion?
4. When a male athlete injects testosterone the testicles generally get smaller. Why does this occur?
5. What happens to spermatogenesis when a male athlete injects testosterone?
6. GnRH agonists are used to treat women with endometriosis. How would testosterone secretion be affected in the short term and in the long term?
7. When a female gets pregnant the corpus luteum of the ovary secretes progesterone. What happens to GnRH, LH, and FSH during pregnancy?
Explanation / Answer
1)Removal of testicals in dogs removes the source of circulating steroids by removing gonads.Reproductive events in male and female dogs are controlled by hypothalamus which releases GnRH.This in turn stimulates pituitary gland to secret FSH and LH.
The communication is mediated by hypothalamus to pituitary glan via GnRH hormones.This is called Hypothalamic-pituitary-gonadal axis.This axis is controlled by negative and positive feedback loop.The hormonal level alteration is dependent on this axis.
After removal of testicals most important hormonal change occures due to removal of negative feedback loop from gonadal steroids back to hypothalamus.Thus results in altered levels of GnRH,FSH,LH.
2)Hypothalamus and pituitary gland controls the level of testesterone secretion.Pitutaru gland on activation secrets FSH and LH .LH will stimulate the production of testesterone.Injury to pituitary gland will not secret Gonadotropic hormones FSH and LH thus testesterone level will decrease.
3)Testesterone synthesis is regulated by Hypothalamic-pituitary-gonadal axis.Increase in level of testesterone through injection feedback loop act on hypothalamus to inhibit the release of GnRH,LH,FSH thus decrease in level of these hormones.
4) tHis condition is known as Testicular atrophy in which tesicals stops secretion of testesterone.As testesterone is provided artificially and not by stimulating GnRH ,testicals will not send signal to Hypothalamic-pituitary-gonadal axis and thus there will be no production will takes place in testicals.
5)Spermatogenesis is highly sensitive to hormone level and temperature.Spermatogenesis is initiated by signaling to hypothalamus to produce FSH an LH.High testesterone levels are enough for spermatogenesis.Level of testesterone is the main concern in the process of spermatogenesis.FSH absence due to negative feedback will have effect on prevention of sperm cells from apoptosis.
6)GnRH agonist affects gonadotrophins and sex hormones.Main side effect of this is sex hormone defficiency-low testesterone levels.
They are agonists of GnRH receptors and work by increase and decrease in the release of GnRH and production of sex hormones by gonads.In short terms ,in females it lowers the eleveted levels of testesterone while in long term GnRh agonists are capable of complete shut down of gonadal testesterone production.
7)Progesterone is produced by corpus leuteum in ovary.In pregnancy progesterone inhibits the release of FSH and LH from pituitary gland to maintain the pregnancy.