524 Obstetrics and Gynecology Board Review •••
❍ What is the most common cause of Cushing syndrome?
Pituitary microadenoma.
❍ What is the main effect and source of inhibin?
Inhibits FSH but not LH, secreted by granulosa cells.
❍ What are inhibin A and inhibin B markers of?
Inhibin A—Corpus luteum function, under control of LH.
Inhibin B—Granulosa cell function, under control of FSH. Elevated in granulosa cell tumors.
❍ What are the effects of activin?
Upregulates FSH receptor expression, and increases pituitary FSH synthesis and secretion. Also, a physiologic
antagonist to inhibin.
❍ What is the main effect and source of follistatin?
Inhibits FSH and FSH response to GnRH. Product of granulosa cells.
❍ What are the effects of high levels of progesterone?
Inhibits GnRH pulses at hypothalamus level and subsequently inhibits secretion of gonadotropins.
❍ What is the source of a majority of the circulating testosterone in a nonpregnant woman?
Peripheral conversion of androstenedione by 17β-hydroxysteroid dehydrogenase. Only 30% to 40% is directly secreted.
❍ What limits peripheral conversion of testosterone to dihydrotestosterone in females?
Higher levels of sex hormone-binding globulin.
Peripheral conversion of testosterone to estrogen by aromatase.
❍ Accumulation of what substance leads to upregulation of LH receptors?
FSH-induced cAMP.
❍ Activation of LH receptors in theca cells leads to production of what substance?
Androstenedione (weak androgen).
❍ In a premenopausal woman, what percentage of estradiol is directly secreted from the ovary?
95%.
❍ What enzymatic deficiency is associated with most cases of the adrenogenital syndrome (congenital adrenal
hyperplasia)?
21-hydroxylase.
❍ What is the most common enzymatic defect seen in congenital adrenal hyperplasia?
A deficiency in C-21 hydroxylation.