Instructor Notes — Chapter 3

Teaching notes

What this chapter is actually for

Two rules, and everything else is the evidence for them:

1. Expect suppression where there is a set-point sensor; don't assume one exists.
2. "Raising the level" is not "reproducing the signal."

Those two sentences do more predictive work than anything else in Part I. A student who leaves with them can reason correctly about growth hormone, secretagogues, GnRH agonists, testosterone, and GLP-1 without having memorized any of them individually.

The chapter is also the least exciting in Part I and students will treat it as review. It isn't — the architecture is what makes Part III legible, and students who skim it end up unable to explain why a secretagogue argument is reasonable, which leaves them with nothing but skepticism-by-default.

Common misconceptions

"A hormone is an ingredient." The dominant frame students arrive with: the body has too little of something, add more, done. The chapter's entire job is dismantling this. The line that works: the system talks back. Then §3.4.

"Suppression means the drug is damaging you." No — suppression is the system working correctly. Students often hear "shuts down your natural production" as evidence of harm. Reframe: it is exactly what a thermostat does when you hold a candle under it, and the thermostat is fine. The legitimate concerns are different ones (duration, recovery, gland atrophy), and separating them from the suppression itself is a useful exercise.

"More is more." §3.5 is the antidote and it is counterintuitive enough that students remember it. The GnRH agonist result — continuous stimulation suppressing the axis — reliably produces audible surprise, which is worth engineering for.

"If it's upstream it's safer." Extremely common in students who have encountered peptide marketing. The §3.4 Hype Check addresses it directly. The key correction: the loop being intact means the loop pushes back, and "preserved feedback" is a mechanistic observation that has been converted into a safety claim without evidence.

"GLP-1 must suppress your own GLP-1." Students who learn §3.4 well over-apply it. §3.9's semaglutide row exists for this and it is worth spending five minutes on, because the reason — no upstream set-point sensor, release is stimulus-triggered — is the reason the rule is a rule rather than a superstition.

The hardest point to teach

Pulsatility as information.

Students accept that hormones are released in pulses. They do not readily accept that the pattern carries content — that the same molecule at the same total exposure means something different depending on its timing.

Two things help. First, the GnRH frequency result: different pulse frequencies preferentially drive LH versus FSH. The information is unambiguously in the rhythm. Second, the therapeutic exploitation: draw the same axis twice, once with pulsatile GnRH (fertility treatment) and once with continuous (leuprolide, cancer treatment), and let students see one receptor producing opposite clinical outcomes.

An analogy that lands: a smoke alarm and a doorbell can use the same speaker. What differs is the pattern, and you respond to them completely differently.

Demonstrations that work

The thermostat with a candle. Physical if possible, verbal otherwise. A thermostat set to 20°C with a candle held under it. The room gets cold, the thermostat reports 20°C, and the heating stays off. The sensor is not broken. The sensor is measuring exactly what it was built to measure. This is the single most effective way to convey why exogenous hormone suppresses endogenous production, and students reuse it for the rest of the term.

Tracing a drug on the board. Draw a blank three-tier axis. Give groups a drug each — recombinant GH, a GHRH analog, leuprolide, degarelix, semaglutide, insulin — and have them place it, mark agonist/antagonist, note the delivery pattern, and predict the feedback response. Ten minutes, and it converts §3.9 from a table into a skill. Semaglutide is the interesting one and should be assigned to a group you expect to argue about it.

Read the label, predict the side effects. Exercise 3.22: have students predict somatostatin analog side effects from §3.3 and §3.6 before opening the label on DailyMed. Then open it. The hit rate is usually high enough to be encouraging and low enough to make the point that mechanism generates hypotheses rather than answers.

Timing

For a 75-minute session:

§3.4 and §3.5 together should get half the session. Everything else is context for them.

Assessment notes

Exercises 3.13, 3.17, 3.24, and 3.28 discriminate well. 3.13 (construct the suppression rule yourself, then test it against GLP-1) is the best single item — a student who derives the rule and correctly identifies the exception has understood the chapter.

3.24 (three verdicts from one system) is the item that most directly prepares students for Chapter 5, and it is worth grading carefully.