Endocrine Regulation and Reproduction
Core concepts
Understand hormones as chemical messengers acting on target cells via receptors; distinguish steroid (intracellular receptors, gene expression) from peptide/protein hormones (membrane receptors, second messengers). Know the hypothalamic–pituitary axis and feedback loops for thyroid, adrenal, and gonadal hormones. For reproduction, know the menstrual cycle phases (follicular, ovulation, luteal), the roles of FSH, LH, estrogen, and progesterone, spermatogenesis, fertilization, and early development.
Traps in questions
- In the menstrual cycle, LH surge triggers ovulation; estrogen peaks just before it.
- Progesterone dominates the luteal phase and maintains the endometrium.
- Steroid hormones cross the membrane and act on intracellular receptors; peptide hormones act on surface receptors.
- The posterior pituitary stores and releases hormones made in the hypothalamus (ADH, oxytocin).
- Negative feedback: high thyroid hormone suppresses TSH.
Worked example / rule of thumb
If progesterone falls (corpus luteum regression), the endometrium sheds → menstruation → FSH rises → new follicle develops. Rule of thumb: name the gland, the hormone, the target, and the feedback direction. For any cycle question, draw the four phases and place the hormone peaks on them.