MCAT Biological and Biochemical Foundations of Living Systems Quiz: 3b Reproductive System Hormonal Control

What this quiz covers

This quiz focuses on 3b Reproductive System Hormonal Control, giving you a quick way to practice the rules, question types, and explanations that matter most for MCAT Biological and Biochemical Foundations of Living Systems.

How to use this quiz

Try each quiz question before looking at the correct answer. Use the explanations to review missed ideas, then come back to similar questions until the pattern feels familiar.

Question 1

1. Sustained elevation of LH and FSH due to constant GnRH receptor occupancy at pituitary gonadotrophs
2. Decreased LH and FSH after 72 hours due to reduced pituitary responsiveness to continuous GnRH stimulation (correct answer)
3. Increased prolactin with secondary suppression of LH and FSH as the primary mechanism of the infusion effect
4. No change in LH and FSH because GnRH acts only on the gonads and not on the anterior pituitary

Explanation: This question tests understanding of GnRH receptor desensitization and the importance of pulsatile hormone signaling. GnRH normally stimulates LH and FSH release through pulsatile secretion, which prevents receptor desensitization at pituitary gonadotrophs. When GnRH is given continuously rather than in pulses, GnRH receptors become desensitized through downregulation and internalization, leading to decreased pituitary responsiveness. After 72 hours of continuous GnRH infusion, LH and FSH levels would be suppressed despite the presence of GnRH. Choice A incorrectly assumes constant receptor occupancy maintains stimulation, ignoring the critical role of pulsatility. A key principle to remember is that many hypothalamic-releasing hormones require pulsatile secretion to maintain target cell responsiveness.

Question 2

1. High estradiol increases LH by stimulating adrenal ACTH secretion, which secondarily triggers ovulation
2. Sustained high estradiol increases LH by inhibiting GnRH secretion, reducing pituitary desensitization
3. High estradiol decreases LH because ovarian steroids exert only negative feedback throughout the cycle
4. Sustained high estradiol switches to positive feedback, increasing LH release from the anterior pituitary (correct answer)

Explanation: This question tests understanding of estradiol's dual feedback effects on gonadotropin secretion. During most of the menstrual cycle, estradiol exerts negative feedback on LH and FSH secretion. However, when estradiol reaches and maintains high levels (>200-300 pg/mL) for approximately 48 hours, it switches to positive feedback at both hypothalamic and pituitary levels. This positive feedback triggers the LH surge necessary for ovulation, representing a unique example of positive feedback in endocrinology. Choice B incorrectly suggests GnRH inhibition increases LH, while choice C fails to recognize the biphasic nature of estradiol feedback. A key concept is that the direction of estradiol feedback depends on both concentration and duration, with sustained high levels uniquely triggering positive feedback.

Question 3

1. Decreased FSH due to reduced inhibin-mediated stimulation of pituitary gonadotrophs
2. Increased FSH due to loss of inhibin negative feedback on the anterior pituitary (correct answer)
3. Decreased LH due to loss of inhibin negative feedback on hypothalamic GnRH neurons
4. Increased TSH due to compensatory upregulation of glycoprotein hormone alpha subunit production

Explanation: This question tests understanding of inhibin B's selective regulation of FSH secretion. Inhibin B, produced by Sertoli cells, specifically suppresses FSH secretion from pituitary gonadotrophs without significantly affecting LH. When inhibin B production is impaired, this selective negative feedback is lost, leading to increased FSH levels while LH remains relatively unchanged due to maintained testosterone feedback. This demonstrates the principle of differential regulation of gonadotropins, where FSH is regulated by both sex steroids and inhibin, while LH is primarily regulated by sex steroids alone. Choice A incorrectly suggests inhibin stimulates rather than inhibits FSH, while choice C wrongly attributes the effect to LH changes. Students should remember that inhibin selectively suppresses FSH, providing fine-tuning of spermatogenesis regulation.

Question 4

1. Reduced energy availability is most consistent with decreased hypothalamic GnRH drive, lowering LH/FSH and ovarian estradiol (correct answer)
2. Low leptin is most consistent with increased pulsatile GnRH release, triggering premature luteinization
3. Low estradiol is most consistent with increased ovarian inhibin causing suppression of LH only
4. Oligomenorrhea is most consistent with elevated ACTH directly inhibiting ovarian aromatase as the primary mechanism

Explanation: This question tests understanding of hormonal control in the reproductive system. Energy availability modulates hypothalamic GnRH via leptin, affecting gonadotropin and steroid levels. Low leptin from reduced energy suppresses GnRH, lowering LH/FSH and estradiol, as in choice A. This aligns with functional hypothalamic amenorrhea in athletes. Choice B fails on the misconception that low leptin stimulates GnRH. For transferable application, evaluate metabolic signals' impact on GnRH drive. Confirm consistency by ensuring low energy links to suppressed reproductive axis.

Question 5

1. Decreased FSH due to lack of ovarian response to pituitary stimulation
2. Increased FSH due to reduced estradiol/inhibin negative feedback at the pituitary (correct answer)
3. Decreased LH due to increased estradiol positive feedback
4. Increased ACTH due to ovarian failure activating the HPA axis as the primary compensatory pathway

Explanation: This question tests understanding of hormonal control in the reproductive system. Loss of ovarian response reduces estradiol and inhibin, decreasing negative feedback. This elevates FSH, as in choice B, mimicking ovarian failure. The intact axis drives compensatory FSH increase. Choice A fails on the misconception of suppressed FSH in failure states. For transferable checks, assess feedback loss in target organ defects. Confirm loop by tracing reduced inhibitors to pituitary elevation.

Question 6

1. Increased endometrial stability due to progesterone withdrawal delaying menstruation
2. Earlier endometrial shedding due to reduced progesterone support of the secretory endometrium (correct answer)
3. Increased LH surge frequency due to progesterone-driven positive feedback in the luteal phase
4. Decreased FSH due to increased inhibin secretion from a regressing corpus luteum

Explanation: This question tests understanding of hormonal control in the reproductive system. Luteal progesterone maintains endometrial stability; early decline prompts shedding. Reduced progesterone causes earlier menses, as in choice B. Low LH pulses contribute to defect. Choice A fails assuming withdrawal delays shedding. For similar scenarios, link progesterone levels to cycle timing. Confirm loop by assessing support for secretory phase.

Question 7

1. Increased GnRH pulse generation due to prolactin stimulation of hypothalamic kisspeptin neurons
2. Suppressed GnRH/LH pulsatility associated with elevated prolactin, delaying follicular maturation (correct answer)
3. Increased oxytocin directly inhibits pituitary LH secretion, independent of hypothalamic input
4. Reduced estrogen causes a compensatory increase in TSH to restore reproductive cycling

Explanation: This question tests understanding of prolactin's inhibitory effects on reproductive function. During lactation, frequent nursing stimulates prolactin secretion, which suppresses GnRH pulsatility at the hypothalamic level, leading to reduced LH and FSH secretion. This physiological mechanism prevents pregnancy during intensive breastfeeding by maintaining anovulation and amenorrhea. The correct answer (B) accurately describes how elevated prolactin suppresses GnRH/LH pulsatility, preventing follicular development and ovulation. Option A incorrectly suggests prolactin stimulates GnRH, option C introduces oxytocin without proper context, and option D incorrectly involves TSH in reproductive regulation. Students should remember that hyperprolactinemia, whether physiological (lactation) or pathological (prolactinoma), consistently suppresses the reproductive axis by inhibiting GnRH pulsatility.

Question 8

1. Decreased LH and FSH due to enhanced negative feedback at the hypothalamus from progesterone receptor activation
2. Increased LH and FSH due to reduced progesterone-mediated negative feedback on GnRH pulse generation (correct answer)
3. Increased prolactin due to loss of dopamine inhibition, leading to increased LH secretion
4. Decreased LH due to direct suppression of pituitary gonadotrophs by estradiol at luteal-phase concentrations

Explanation: This question tests understanding of progesterone's role in negative feedback regulation of the hypothalamic-pituitary-gonadal axis. During the luteal phase, progesterone normally suppresses GnRH pulse frequency and amplitude, thereby reducing LH and FSH secretion. When a progesterone receptor antagonist blocks this negative feedback, the hypothalamus increases GnRH release, leading to elevated gonadotropin levels. The data shows LH increased from 3 to 14 IU/L and FSH from 4 to 9 IU/L after SPRA administration, confirming loss of progesterone-mediated suppression. Choice A incorrectly suggests the antagonist would enhance negative feedback, while choices C and D propose mechanisms inconsistent with the observed increase in both gonadotropins. A key check for students: when progesterone signaling is blocked, expect increased gonadotropin secretion due to disinhibition of GnRH.

Question 9

1. Chronic GnRH agonist exposure desensitizes pituitary gonadotrophs, lowering LH/FSH and reducing ovarian estradiol production (correct answer)
2. GnRH agonists block ovarian estrogen receptors, reducing estradiol action without altering gonadotropins
3. GnRH agonists increase estradiol by mimicking LH at the ovary, enhancing aromatase activity
4. Reduced estradiol is caused by increased cortisol negative feedback on CRH, which suppresses GnRH release

Explanation: This question tests understanding of GnRH agonist effects on pituitary desensitization. Initial GnRH agonist exposure causes a brief stimulatory phase, but chronic exposure leads to GnRH receptor downregulation and desensitization of gonadotrophs. This results in profoundly suppressed LH and FSH secretion, creating a reversible medical castration state with very low sex steroid levels. The data shows dramatic suppression: LH fell from 6.8 to 0.9 IU/L and estradiol from 140 to 18 pg/mL, explaining both symptom improvement and menopausal side effects. Choice B incorrectly suggests receptor blockade, choice C proposes stimulation rather than suppression, and choice D invokes an unrelated cortisol mechanism. Key concept: chronic GnRH agonist exposure paradoxically suppresses the reproductive axis through pituitary desensitization.

Question 10

1. Exogenous estrogen and progestin increase GnRH pulse frequency, amplifying LH and FSH release
2. Exogenous estrogen and progestin provide negative feedback on the hypothalamus and pituitary, reducing gonadotropins and preventing follicular maturation (correct answer)
3. The progestin directly lyses the corpus luteum, lowering estradiol and triggering an LH surge
4. Suppressed gonadotropins are primarily caused by increased thyroid hormone production following estrogen exposure

Explanation: This question tests understanding of how combined oral contraceptives suppress ovulation through hormonal feedback. Exogenous estrogen and progestin in contraceptives provide sustained negative feedback on the hypothalamus and pituitary, suppressing GnRH pulsatility and reducing LH and FSH secretion. Without adequate gonadotropins, follicular development cannot proceed, preventing dominant follicle selection and ovulation. The data confirms this mechanism: LH dropped from 9 to 2 IU/L, FSH from 7 to 3 IU/L, and estradiol from 160 to 40 pg/mL, with no dominant follicle visible. Choice A incorrectly suggests increased GnRH, choice C proposes direct corpus luteum effects (which doesn't exist mid-cycle), and choice D invokes an unrelated thyroid mechanism. Students should recognize: contraceptive steroids work by suppressing gonadotropins through negative feedback.

Question 11

1. Decreased FSH due to increased estradiol negative feedback on pituitary gonadotrophs
2. Increased FSH due to reduced estradiol-mediated negative feedback at the hypothalamus and pituitary (correct answer)
3. Decreased GnRH due to direct inhibition of hypothalamic steroid synthesis by the drug
4. Increased prolactin as the primary driver of reduced estradiol production

Explanation: This question tests understanding of aromatase inhibition and its effects on reproductive hormone feedback. Aromatase converts androgens to estrogens, and inhibiting this enzyme reduces estradiol production from ovarian follicles. With decreased estradiol, there is reduced negative feedback on the hypothalamus and pituitary, leading to increased GnRH secretion and subsequently increased FSH (and LH) release. The elevated FSH represents the pituitary's attempt to stimulate ovarian follicle development and estrogen production. Choice A incorrectly suggests decreased FSH with increased estradiol, which contradicts the mechanism of aromatase inhibition. Students should remember that reducing sex steroid levels removes negative feedback, leading to compensatory increases in gonadotropins.

Question 12

1. Increased LH and increased FSH due to enhanced androgen signaling at the hypothalamus
2. Decreased LH and decreased FSH due to negative feedback from elevated circulating androgens (correct answer)
3. No change in LH and FSH because testosterone regulates only secondary sex characteristics, not pituitary output
4. Increased LH with decreased FSH because testosterone selectively inhibits FSH but stimulates LH secretion

Explanation: This question tests understanding of exogenous testosterone's effects on the hypothalamic-pituitary-testicular axis. Exogenous testosterone provides strong negative feedback to the hypothalamus and pituitary, suppressing GnRH secretion and subsequently reducing both LH and FSH release. This suppression of LH removes the stimulus for intratesticular testosterone production by Leydig cells, while FSH suppression impairs Sertoli cell function and spermatogenesis. Choice A incorrectly suggests increased gonadotropins despite high circulating androgens, failing to recognize negative feedback. A critical concept for students is that exogenous testosterone suppresses the HPG axis, which is why it can cause testicular atrophy and infertility despite high serum testosterone levels.

Question 13

1. Decreased GnRH pulse frequency with decreased LH and decreased FSH
2. Increased LH and increased FSH due to reduced negative feedback on gonadotropin secretion (correct answer)
3. Increased progesterone with decreased LH due to enhanced luteal-phase signaling
4. Increased thyroid-stimulating hormone (TSH) with decreased LH due to shared pituitary trophic regulation

Explanation: This question tests understanding of negative feedback loops in the hypothalamic-pituitary-gonadal axis. In normal physiology, ovarian steroids (estrogen and progesterone) exert negative feedback on the hypothalamus and pituitary to regulate gonadotropin secretion. When ovarian steroid production is chronically low, this negative feedback is removed, leading to increased GnRH pulse frequency and amplitude. Consequently, both LH and FSH levels rise as the pituitary attempts to stimulate the underactive ovaries. Choice A incorrectly suggests decreased GnRH, while choice C wrongly introduces progesterone increase when ovarian function is impaired. Students should remember that loss of negative feedback leads to increased upstream hormone secretion in endocrine axes.

Question 14

1. Decreased LH with decreased testosterone because blocking estrogen receptors reduces gonadotropin release
2. Increased LH with increased testosterone because reduced estrogen-mediated negative feedback increases gonadotropin drive (correct answer)
3. No change in LH because estrogen receptors regulate only FSH, not LH
4. Increased cortisol with decreased testosterone because the SERM directly activates the adrenal cortex

Explanation: This question tests understanding of estrogen's role in male reproductive hormone regulation. In males, testosterone is partially converted to estradiol by aromatase, and this estradiol provides negative feedback to the hypothalamus and pituitary. When a SERM blocks estrogen receptors at these sites, the negative feedback is removed, leading to increased GnRH and subsequently increased LH secretion. The elevated LH then stimulates Leydig cells to produce more testosterone. Choice A incorrectly suggests that blocking estrogen receptors would decrease gonadotropins, failing to recognize the removal of negative feedback. A key concept is that estrogen plays an important regulatory role in male reproductive hormone feedback, not just in females.

Question 15

1. Increased GnRH with increased LH because prolactin stimulates hypothalamic GnRH neurons
2. Decreased GnRH pulse activity with decreased LH/FSH due to prolactin-associated suppression of hypothalamic drive (correct answer)
3. Increased FSH with decreased LH because prolactin selectively inhibits LH but not FSH
4. Decreased TSH with decreased LH because prolactin primarily downregulates thyrotroph function

Explanation: This question tests understanding of prolactin's inhibitory effects on reproductive function. Elevated prolactin, as occurs during lactation, suppresses GnRH pulse frequency and amplitude at the hypothalamic level through both direct effects and by altering kisspeptin signaling. This reduction in GnRH pulsatility leads to decreased LH and FSH secretion from the pituitary, resulting in anovulation and amenorrhea. This mechanism serves as a natural contraceptive during exclusive breastfeeding. Choice A incorrectly suggests prolactin stimulates GnRH, while choice C wrongly proposes selective LH inhibition. Students should remember that hyperprolactinemia from any cause (lactation, prolactinoma, medications) suppresses reproductive function through hypothalamic inhibition.

Question 16

1. hCG mimics LH signaling at Leydig cells, increasing testosterone despite potential suppression of endogenous LH via negative feedback (correct answer)
2. hCG mimics FSH signaling at Sertoli cells, increasing testosterone by directly stimulating spermatogenesis
3. hCG blocks androgen receptors in the hypothalamus, increasing GnRH and thereby increasing testosterone
4. hCG reduces testosterone synthesis by inhibiting cholesterol transport into mitochondria as part of a protective feedback loop

Explanation: This question tests understanding of hCG's biological activity and its similarity to LH. Human chorionic gonadotropin (hCG) shares structural homology with LH and can bind to and activate LH receptors on Leydig cells in the testes. This LH-like activity stimulates testosterone production through the same signaling cascade as endogenous LH, involving cAMP-mediated activation of steroidogenic enzymes. Despite potential negative feedback from elevated testosterone on endogenous LH secretion, the exogenous hCG maintains Leydig cell stimulation. Choice B incorrectly attributes hCG action to FSH-like effects, while choice D suggests an inhibitory action contrary to hCG's known stimulatory effects. Students should remember that hCG acts as an LH analog, which is why it's used therapeutically to stimulate testosterone production.

Question 17

1. Premature LH surge due to progesterone-mediated positive feedback on the hypothalamus
2. Suppressed LH surge due to progestin-associated negative feedback on GnRH/LH signaling (correct answer)
3. Increased FSH due to progesterone acting directly on ovarian granulosa cells to increase aromatase
4. No effect on ovulation because progesterone receptors are expressed only in the uterus, not the brain or pituitary

Explanation: This question tests understanding of progesterone's role in preventing ovulation through feedback inhibition. Continuous progesterone receptor activation suppresses the LH surge through negative feedback at both hypothalamic and pituitary levels, preventing the GnRH surge and subsequent LH surge necessary for ovulation. This mechanism underlies the contraceptive effect of progestin-only pills and long-acting reversible contraceptives. Without the LH surge, the dominant follicle cannot complete maturation and ovulate, despite adequate estradiol levels. Choice A incorrectly suggests progesterone causes positive feedback for LH surge, while choice D wrongly claims progesterone receptors are absent in the brain. Students should remember that sustained progesterone exposure prevents ovulation by suppressing the LH surge.

Question 18

1. Increased GnRH pulse frequency from the hypothalamus, raising LH despite exogenous testosterone
2. Reduced pituitary gonadotropin release due to negative feedback, lowering Leydig cell stimulation (correct answer)
3. Increased prolactin secretion, which directly suppresses spermatogenesis independent of LH/FSH
4. Upregulated TSH secretion to compensate for decreased intratesticular testosterone

Explanation: This question tests understanding of negative feedback in the hypothalamic-pituitary-gonadal axis. In males, testosterone normally exerts negative feedback on the hypothalamus and pituitary, suppressing GnRH, LH, and FSH release. When exogenous testosterone is administered via transdermal patch, it adds to circulating testosterone levels, enhancing this negative feedback and reducing gonadotropin secretion. The correct answer (B) accurately describes how reduced LH from the pituitary leads to decreased stimulation of Leydig cells, which are responsible for intratesticular testosterone production. Option A incorrectly suggests increased GnRH frequency, which would oppose negative feedback, while option C introduces prolactin without justification, and option D incorrectly involves TSH, which is part of the thyroid axis, not the reproductive axis. To verify hormonal feedback direction, students should check whether exogenous hormones suppress (negative feedback) or stimulate (positive feedback) upstream regulatory hormones.

Question 19

1. Decreased GnRH pulse frequency due to enhanced negative feedback at the hypothalamus
2. Increased LH secretion due to reduced negative feedback signaling in the luteal phase (correct answer)
3. Decreased FSH secretion due to increased inhibin release from granulosa cells
4. Increased prolactin secretion due to disinhibition of pituitary lactotrophs

Explanation: This question tests understanding of hormonal control in the reproductive system. Hormonal regulation in reproduction involves feedback loops where gonadal steroids modulate hypothalamic and pituitary hormone release. In the luteal phase, progesterone exerts negative feedback to suppress LH secretion. Administering a progesterone receptor antagonist reduces this negative feedback, leading to increased LH secretion as described in choice B. A common misconception is that antagonists directly alter hormone synthesis, but here the effect is on signaling, not production, making choice A incorrect as GnRH frequency would not decrease with reduced feedback. To verify similar questions, check if the intervention disrupts negative or positive feedback loops consistently. Always confirm that the outcome aligns with the phase-specific dominance of progesterone or estrogen feedback.

Question 20

1. Suppressed FSH and LH due to sustained negative feedback preventing the LH surge (correct answer)
2. Elevated FSH due to reduced ovarian steroidogenesis from estradiol exposure
3. Elevated LH due to estradiol-driven positive feedback occurring at all concentrations
4. Increased ACTH due to estradiol-mediated stimulation of the adrenal cortex

Explanation: This question tests understanding of hormonal control in the reproductive system. Hormonal regulation relies on estrogen's biphasic feedback: negative at low levels and positive at high, surge-inducing levels. Continuous estradiol delivery maintains steady high levels, enforcing negative feedback and suppressing gonadotropins. This prevents the LH surge, as sustained elevation blocks the positive feedback threshold, supporting choice A. A distractor like choice C fails due to the misconception that estrogen always stimulates positive feedback, ignoring concentration and duration effects. For similar queries, verify if the intervention mimics physiologic pulsatility or imposes constant signaling. Ensure feedback loop consistency by mapping hormone levels to expected pituitary responses.