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Reproductive hormones aren't just about making babies—they're your window into understanding feedback loops, endocrine signaling hierarchies, and target tissue specificity. In Bio 20300, you'll be tested on how these hormones communicate across the hypothalamic-pituitary-gonadal (HPG) axis, how negative feedback maintains homeostasis, and why timing matters (think pulsatile release patterns and cyclical changes). These concepts show up repeatedly in exam questions about endocrine regulation.
Don't just memorize which gland secretes what. Know why GnRH must be pulsatile, how the same hormone can have different effects in males versus females, and what happens when feedback mechanisms fail. If you understand the underlying logic—command hormones from the brain, tropic hormones from the pituitary, and effector hormones from the gonads—you'll nail both multiple choice and short-answer questions.
These hormones sit at the top of the reproductive hierarchy, acting as master regulators that control downstream hormone release. The hypothalamus integrates neural and hormonal signals, while the pituitary translates those signals into commands for the gonads.
Compare: FSH vs. LH—both are anterior pituitary gonadotropins regulated by GnRH, but FSH primarily supports gamete development (follicles/sperm) while LH drives hormone production and ovulation. Exam tip: if asked about the LH surge, connect it to positive feedback from estrogen.
These are the effector hormones—produced by the gonads, they carry out the actual work of developing sex characteristics, preparing for reproduction, and maintaining pregnancy. All are derived from cholesterol and are lipid-soluble, meaning they cross cell membranes and bind intracellular receptors.
Compare: Estrogen vs. Progesterone—both are ovarian steroids, but estrogen dominates the follicular phase (building the endometrium) while progesterone dominates the luteal phase (maintaining it). On an FRQ about the menstrual cycle, distinguish their timing and target tissue effects.
These hormones fine-tune the system by providing negative feedback to the pituitary, preventing overproduction of gonadotropins. Without these brakes, the reproductive axis would spiral out of control.
Compare: Inhibin vs. Testosterone/Estrogen feedback—all provide negative feedback to the pituitary, but inhibin specifically targets FSH while gonadal steroids suppress both FSH and LH (and GnRH at the hypothalamus). Know which feedback pathway controls what.
These hormones support reproduction beyond conception—maintaining pregnancy, preparing for birth, and enabling nursing. They demonstrate how the endocrine system adapts to dramatically different physiological states.
Compare: Prolactin vs. Oxytocin in lactation—prolactin makes the milk (synthesis), oxytocin releases it (ejection). Both increase with suckling, but through different mechanisms. This distinction is a common exam question.
| Concept | Best Examples |
|---|---|
| HPG axis command hormones | GnRH, FSH, LH |
| Gonadal steroids | Estrogen, Progesterone, Testosterone |
| Negative feedback to pituitary | Inhibin, Testosterone, Estrogen, Progesterone |
| Pregnancy maintenance | hCG, Progesterone |
| Lactation hormones | Prolactin (synthesis), Oxytocin (ejection) |
| Positive feedback examples | Estrogen → LH surge; Oxytocin → uterine contractions |
| Anterior pituitary hormones | FSH, LH, Prolactin |
| Posterior pituitary hormones | Oxytocin |
Which two hormones are both produced by the anterior pituitary and both regulated by GnRH, yet have distinct target cells in the gonads? What does each target?
Compare the roles of estrogen and progesterone in the menstrual cycle—during which phase does each dominate, and what is each preparing the endometrium to do?
How does inhibin's feedback mechanism differ from testosterone's feedback mechanism in males? Which pituitary hormone does each primarily suppress?
If the corpus luteum degenerates before the placenta can produce sufficient progesterone, what would happen to the pregnancy? Which hormone normally prevents this, and how?
Contrast prolactin and oxytocin in breastfeeding: which hormone is responsible for milk production versus milk release, and what stimulus increases both?