Reproductive Hormones and Cycle Phases: GnRH, FSH, LH, Estrogen, and Progesterone

How does GnRH regulate reproduction?

Stimulates release of FSH and LH from the anterior pituitary.

How does FSH support follicular development?

Stimulates follicular growth and promotes estrogen synthesis.

How does LH contribute to ovulation?

Stimulates ovulation and forms the corpus luteum.

How does estrogen (E₂) influence the estrous cycle?

Promotes the LH surge and causes estrus behavior.

How does progesterone (P₄) regulate reproduction?

Inhibits GnRH and prepares the uterine environment.

How do GnRH and LH work together during ovulation?

GnRH stimulates LH release, and LH triggers ovulation and CL formation.

How do FSH and estrogen work together?

FSH stimulates follicular development, and developing follicles produce estrogen.

Why is estrogen important before ovulation?

Promotes the LH surge and stimulates estrus behavior.

Why is progesterone important after ovulation?

Suppresses GnRH release and prepares and maintains the uterine environment.

How does the corpus luteum (CL) influence the estrous cycle?

Secretes progesterone and helps maintain conditions for pregnancy.

How does progesterone affect GnRH?

Progesterone inhibits GnRH release and reduces stimulation of FSH and LH.

How do estrogen levels change before ovulation?

Estrogen (E₂) rises during proestrus and peaks right before ovulation.

How do progesterone levels change around estrus?

Progesterone (P₄) drops before estrus and remains low during ovulation.

How does progesterone change after ovulation?

Begins increasing during metestrus and peaks during diestrus.

How does estrogen influence estrus behavior?

Estrogen rises before ovulation and stimulates standing heat/estrus behavior.

Why does ovulation occur during estrus?

Estrogen peaks and promotes the LH surge, triggering ovulation.

How does diestrus differ hormonally from estrus?

Diestrus has high progesterone, while estrus has high estrogen and low progesterone.

Why is progesterone highest during diestrus?

The corpus luteum is fully functional and secretes progesterone.

How does the corpus luteum affect the estrous cycle?

Produces progesterone and suppresses another ovulation.

Why does progesterone decline before estrus?

Corpus luteum regresses, allowing follicular activity.

How do hormone levels change during proestrus?

Estrogen rises and progesterone declines.

How do hormone levels change during metestrus?

Estrogen declines after ovulation, and progesterone begins increasing.

Why is estrogen low during diestrus?

Follicular activity is reduced, and progesterone is the dominant hormone.

How does ovulation relate to hormone peaks?

Estrogen peaks before ovulation, and progesterone rises after ovulation.

How do estrogen and progesterone interact during the cycle?

Estrogen dominates before ovulation, and progesterone dominates after ovulation.

Why is progesterone low during estrus?

Corpus luteum has regressed, allowing ovulation and estrus behavior.

How does the estrous cycle return to estrus again?

Corpus luteum regresses, progesterone decreases, and estrogen rises again.

Why is diestrus the longest phase of the cycle?

Corpus luteum remains active for many days, and progesterone stays elevated.

How does metestrus transition into diestrus?

Corpus luteum matures, and progesterone continues increasing.

Why is estrus called the 'heat' period?

Estrogen levels are high, and the female displays receptive breeding behavior.

How does progesterone prepare the uterus?

Maintains uterine environment and supports possible pregnancy establishment.

Why must the corpus luteum regress if pregnancy does not occur?

Progesterone must decline to restart estrus and ovulation.

How does estrogen contribute to ovulation timing?

Rising estrogen stimulates LH surge, which induces ovulation.

Why is progesterone considered inhibitory in the cycle?

Suppresses GnRH release and prevents another ovulation during diestrus.

How do the follicular and luteal phases differ?

Follicular phase = high estrogen; Luteal phase = high progesterone.

How does the estrous cycle hormonally prepare for pregnancy?

Ovulation releases the oocyte, and progesterone prepares and maintains the uterus.