Why FHS levels in hypopituitarism are decreased?
I think you meant FSH (Follicle Stimulating Hormone). The hypothalamus releases a hormone called Gonadotropin-Releasing Hormone (GnRH)
GnRH travels to the Pituitary and causes the release of FSH and Lutenizing (LH) hormone. The pituitary has 2 parts, the anterior and posterior pituitary.
If there is a decrease in the function of the anterior pituitary (hypopituitarism) then when the Gonadotropin-Releasing Hormone travels to the pituitary, the pituitary will not respond. Therefore, there will be no (or a decrease) release of FSH.
Most common reason for hypopituitarism is a tumor pushing on the gland causing a decrease in function.
The hypopituitarism is a disorder that affects the pituitary gland and if the pituitary gland fails to secrete hormones that stimulate endocrine gland, the patient can experience one or more hormones deficiency.
The list of affected hormons consists of the followings: TSH deficiency, ADH deficiency, GH deficiency, LH and FSH deficiencies.
The follicle-stimulating hormone (FSH) deficiency has the same effect as luteinizing hormone deficiency (LH). Both defficiencies affect men's fertility in men women's menstruation.
Since FSH deficiency represents the loss of follicle-stimulating hormone, hence, the decreased levels of follicle-stimulating hormone indicate the presence of hypopituitarism.