---
title: "Hormonal Communication"
book: "Primary & Middle School Biology"
subject: biology
language: en
chapter: 61
exercises: 12
source: https://one-course.com/books/biology/1/en/chapter/61-hormonal-communication
---

# Chapter 61 — Hormonal Communication

[Puberty](https://one-course.com/books/biology/1/en/chapter/56-puberty#def-g8-puberty-puberty) introduced them ([Definition 56.4](https://one-course.com/books/biology/1/en/chapter/56-puberty#def-g8-puberty-hormones)); the pill exploits them ([Definition 59.3](https://one-course.com/books/biology/1/en/chapter/59-contraception#def-g8-contraception-pill)); the fright’s hot wave delivered one mid-sprint ([Example 60.10](https://one-course.com/books/biology/1/en/chapter/60-nervous-communication#ex-g8-nervous-communication-cases)). The postal service deserves its own tour: the [glands](#def-g8-hormonal-communication-glands) that write the letters, the [blood](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#prop-g4-journey-of-food-absorb) that carries them, the addressing trick that makes a broadcast precise — and the [feedback](#prop-g8-hormonal-communication-feedback) loops that keep the whole correspondence in balance.

## 61.1 Glands, hormones, targets

**Definition 61.1 (The endocrine glands).**

A *gland* whose product is released *into the [blood](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#prop-g4-journey-of-food-absorb)* (rather than down a duct, like [saliva](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#def-g4-journey-of-food-tract)’s) is an *endocrine* gland, and its products are the *hormones*. The main writers: the brain-base *control gland* — [puberty](https://one-course.com/books/biology/1/en/chapter/56-puberty#def-g8-puberty-puberty)’s starter, and the conductor of most of the others; the *thyroid* in the neck — its hormone sets the whole body’s running pace; the *adrenal* caps on the [kidneys](https://one-course.com/books/biology/1/en/chapter/53-removing-the-wastes#def-g7-removing-wastes-kidneys) — the alarm hormone of frights and sprints; the *pancreas* — its hormone manages the [blood](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#prop-g4-journey-of-food-absorb)’s [glucose](https://one-course.com/books/biology/1/en/chapter/49-organs-at-work#prop-g7-organs-at-work-bill); and the *[ovaries](https://one-course.com/books/biology/1/en/chapter/57-the-reproductive-systems#def-g8-reproductive-systems-female) and [testes](https://one-course.com/books/biology/1/en/chapter/57-the-reproductive-systems#def-g8-reproductive-systems-male)* — the cycle and rebuild hormones of [Chapter 57](https://one-course.com/books/biology/1/en/chapter/57-the-reproductive-systems#ch-g8-reproductive-systems).

**Proposition 61.2 (Addressing by receptor).**

The [blood](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#prop-g4-journey-of-food-absorb) delivers every [hormone](#def-g8-hormonal-communication-glands) everywhere ([Example 56.5](https://one-course.com/books/biology/1/en/chapter/56-puberty#ex-g8-puberty-sites)) — yet each acts only on its *target organs*: the [cells](https://one-course.com/books/biology/1/en/chapter/29-a-first-look-at-cells#def-g5-first-look-at-cells-cell) built with docking sites, *receptors*, for that messenger. Broadcast carriage, receiver-side addressing: a letter every house receives, readable only where the key fits. (The [synapse](https://one-course.com/books/biology/1/en/chapter/60-nervous-communication#def-g8-nervous-communication-synapse)’s docking of [Definition 60.4](https://one-course.com/books/biology/1/en/chapter/60-nervous-communication#def-g8-nervous-communication-synapse) is the same trick at nanometre range.)

**Proof.** *Admitted at this level.* ∎

**Example 61.3 (One messenger’s tour: the alarm hormone).**

A near-miss on the bicycle: the adrenal [glands](#def-g8-hormonal-communication-glands) dump their alarm [hormone](#def-g8-hormonal-communication-glands) into the [blood](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#prop-g4-journey-of-food-absorb), and within seconds — one circulation lap ([Example 27.2](https://one-course.com/books/biology/1/en/chapter/27-the-heart-and-the-blood#ex-g4-heart-and-blood-round)) — every fitted receiver responds at once: the [heart](https://one-course.com/books/biology/1/en/chapter/27-the-heart-and-the-blood#def-g4-heart-and-blood-heart)’s pace jumps, the airways widen, the [liver](https://one-course.com/books/biology/1/en/chapter/50-digestion-and-nutrients#prop-g7-digestion-and-nutrients-absorption) releases banked [glucose](https://one-course.com/books/biology/1/en/chapter/49-organs-at-work#prop-g7-organs-at-work-bill) ([Example 50.9](https://one-course.com/books/biology/1/en/chapter/50-digestion-and-nutrients#ex-g7-digestion-and-nutrients-breadtrace)’s bank, called), [muscle](https://one-course.com/books/biology/1/en/chapter/17-bones-and-muscles#def-g3-bones-and-muscles-muscle) [vessels](https://one-course.com/books/biology/1/en/chapter/27-the-heart-and-the-blood#def-g4-heart-and-blood-vessels) widen and the [digestive tract](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#def-g4-journey-of-food-tract)’s narrow ([Proposition 49.4](https://one-course.com/books/biology/1/en/chapter/49-organs-at-work#prop-g7-organs-at-work-supply)’s rerouting, hormone-held), and the [skin](https://one-course.com/books/biology/1/en/chapter/5-the-five-senses#def-g1-the-five-senses-sense) goes pale and prickling. One letter, six answers, one coordinated state: ready.

## 61.2 Balance by feedback

**Proposition 61.4 (The feedback principle).**

[Hormone](#def-g8-hormonal-communication-glands) systems regulate themselves by *feedback*: the writing [gland](#def-g8-hormonal-communication-glands) *monitors the result* of its own letters, and slows when the result is reached — a thermostat, not a tap. The showcase is [blood](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#prop-g4-journey-of-food-absorb) [glucose](https://one-course.com/books/biology/1/en/chapter/49-organs-at-work#prop-g7-organs-at-work-bill): after a meal, the rising [glucose](https://one-course.com/books/biology/1/en/chapter/49-organs-at-work#prop-g7-organs-at-work-bill) itself triggers the pancreas’s storage [hormone](#def-g8-hormonal-communication-glands); [glucose](https://one-course.com/books/biology/1/en/chapter/49-organs-at-work#prop-g7-organs-at-work-bill) banked, the level falls, and the secretion subsides with it; between meals a partner [hormone](#def-g8-hormonal-communication-glands) releases the bank the other way. The level rides a narrow lane, day and night, with no conscious driver.

**Proof.** *Admitted at this level.* ∎

**Example 61.5 (When feedback fails: diabetes).**

In *diabetes*, the [storage-hormone](#def-g8-hormonal-communication-glands) signal fails — the pancreas stops writing it, or the receivers stop answering. [Glucose](https://one-course.com/books/biology/1/en/chapter/49-organs-at-work#prop-g7-organs-at-work-bill) piles up in the [blood](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#prop-g4-journey-of-food-absorb) after every meal; the [kidney](https://one-course.com/books/biology/1/en/chapter/53-removing-the-wastes#def-g7-removing-wastes-kidneys)’s reclaiming is overwhelmed and sugar appears in the [urine](https://one-course.com/books/biology/1/en/chapter/53-removing-the-wastes#def-g7-removing-wastes-kidneys) — [Example 53.5](https://one-course.com/books/biology/1/en/chapter/53-removing-the-wastes#ex-g7-removing-wastes-thrift)’s classic signal, explained at last. Treatment is applied chapter: measured doses of the missing [hormone](#def-g8-hormonal-communication-glands), timed to meals — the letter written by syringe. Millions live well on exactly this arrangement.

**Remark 61.6 (The two systems in partnership).**

[Proposition 60.8](https://one-course.com/books/biology/1/en/chapter/60-nervous-communication#prop-g8-nervous-communication-compare)’s telegraph and post are one administration. The brain-base control [gland](#def-g8-hormonal-communication-glands) is the interface: [nervous system](https://one-course.com/books/biology/1/en/chapter/33-the-brain-in-command#def-g5-brain-in-command-system) above, [hormones](#def-g8-hormonal-communication-glands) below — the cyclist’s fright ran nerve-first, hormone-sustained; [puberty](https://one-course.com/books/biology/1/en/chapter/56-puberty#def-g8-puberty-puberty) runs hormone-slow under a brain-based conductor; the sheep of [Example 55.2](https://one-course.com/books/biology/1/en/chapter/55-reproduction-and-the-environment#ex-g8-reproduction-and-environment-lambs) turn day-length (a nervous perception) into breeding [hormones](#def-g8-hormonal-communication-glands). Fast wires where speed matters, slow post where the program must run for months, and translation offices between.

## 61.3 Reading a hormone system

**Method 61.7 (The four questions of any hormone).**

For any [hormone](#def-g8-hormonal-communication-glands) you meet, establish:

1. *writer* : which [gland](#def-g8-hormonal-communication-glands) , into the [blood](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#prop-g4-journey-of-food-absorb) , on what trigger?
2. *receivers* : which [target organs](#prop-g8-hormonal-communication-address) carry its receptors, and what does each do on delivery?
3. *[feedback](#prop-g8-hormonal-communication-feedback)* : what result reports back, and how is over-writing prevented?
4. *failure and use* : what happens when the letter fails — and does medicine imitate it (the pill, the diabetic’s doses)?

**Example 61.8 (The method on the thyroid’s pace-setter).**

Writer: the thyroid, conducted by the control [gland](#def-g8-hormonal-communication-glands). Receivers: nearly every [cell](https://one-course.com/books/biology/1/en/chapter/29-a-first-look-at-cells#def-g5-first-look-at-cells-cell) — the [hormone](#def-g8-hormonal-communication-glands) sets the rate of [Proposition 46.5](https://one-course.com/books/biology/1/en/chapter/46-what-is-respiration#prop-g7-what-is-respiration-power)’s slow fire. [Feedback](#prop-g8-hormonal-communication-feedback): the control [gland](#def-g8-hormonal-communication-glands) reads the level and trims its conducting. Failure: too little, and the whole engine idles — tiredness, cold, slowed everything; too much, and it races. Use: the missing [hormone](#def-g8-hormonal-communication-glands) is a daily tablet — among medicine’s oldest letters-by-post.

## 61.4 Exercises

**Exercise 61.1 ★.**

What makes a [gland](#def-g8-hormonal-communication-glands) endocrine? Name four, with one [hormone](#def-g8-hormonal-communication-glands) role each.

**Solution of Exercise 61.1.**

Releasing its product into the [blood](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#prop-g4-journey-of-food-absorb) rather than down a duct. The brain-base control [gland](#def-g8-hormonal-communication-glands): conductor of the others and [puberty](https://one-course.com/books/biology/1/en/chapter/56-puberty#def-g8-puberty-puberty)’s starter. The thyroid: the body’s pace-setter. The adrenals: the alarm [hormone](#def-g8-hormonal-communication-glands). The pancreas: [blood-glucose](https://one-course.com/books/biology/1/en/chapter/49-organs-at-work#prop-g7-organs-at-work-bill) management. ([Ovaries](https://one-course.com/books/biology/1/en/chapter/57-the-reproductive-systems#def-g8-reproductive-systems-female)/[testes](https://one-course.com/books/biology/1/en/chapter/57-the-reproductive-systems#def-g8-reproductive-systems-male): the cycle and rebuild [hormones](#def-g8-hormonal-communication-glands).)

**Exercise 61.2 ★.**

The [blood](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#prop-g4-journey-of-food-absorb) delivers everywhere; [hormones](#def-g8-hormonal-communication-glands) act somewhere. Resolve the paradox.

**Solution of Exercise 61.2.**

Carriage is broadcast, addressing is receiver-side: only [cells](https://one-course.com/books/biology/1/en/chapter/29-a-first-look-at-cells#def-g5-first-look-at-cells-cell) fitted with the [hormone](#def-g8-hormonal-communication-glands)’s receptors respond. Every house gets the letter; only the fitting key opens it.

**Exercise 61.3 ★.**

List four of the alarm [hormone](#def-g8-hormonal-communication-glands)’s six answers, each with its serving chapter.

**Solution of Exercise 61.3.**

[Heart](https://one-course.com/books/biology/1/en/chapter/27-the-heart-and-the-blood#def-g4-heart-and-blood-heart) pace up ([Chapter 52](https://one-course.com/books/biology/1/en/chapter/52-the-heart-and-circulation#ch-g7-heart-and-circulation)); airways widened ([Chapter 51](https://one-course.com/books/biology/1/en/chapter/51-the-lungs-and-gas-exchange#ch-g7-lungs-and-gas-exchange)); the [liver](https://one-course.com/books/biology/1/en/chapter/50-digestion-and-nutrients#prop-g7-digestion-and-nutrients-absorption)’s [glucose](https://one-course.com/books/biology/1/en/chapter/49-organs-at-work#prop-g7-organs-at-work-bill) bank released ([Chapter 50](https://one-course.com/books/biology/1/en/chapter/50-digestion-and-nutrients#ch-g7-digestion-and-nutrients)); [blood](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#prop-g4-journey-of-food-absorb) rerouted to [muscles](https://one-course.com/books/biology/1/en/chapter/17-bones-and-muscles#def-g3-bones-and-muscles-muscle) ([Chapter 49](https://one-course.com/books/biology/1/en/chapter/49-organs-at-work#ch-g7-organs-at-work)) — with pale prickling [skin](https://one-course.com/books/biology/1/en/chapter/5-the-five-senses#def-g1-the-five-senses-sense) completing the set.

**Exercise 61.4 ★.**

State the [feedback](#prop-g8-hormonal-communication-feedback) principle, and its showcase.

**Solution of Exercise 61.4.**

The writing [gland](#def-g8-hormonal-communication-glands) monitors its letters’ result and slows as the goal is reached — thermostat, not tap. Showcase: [blood](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#prop-g4-journey-of-food-absorb) [glucose](https://one-course.com/books/biology/1/en/chapter/49-organs-at-work#prop-g7-organs-at-work-bill), banked on the rise and released on the fall by the pancreas’s paired [hormones](#def-g8-hormonal-communication-glands).

**Exercise 61.5 ★.**

What fails in [diabetes](#ex-g8-hormonal-communication-diabetes), and what re-appears at the [kidney](https://one-course.com/books/biology/1/en/chapter/53-removing-the-wastes#def-g7-removing-wastes-kidneys) because of it?

**Solution of Exercise 61.5.**

The [storage-hormone](#def-g8-hormonal-communication-glands) signal — unwritten, or unanswered by its receivers. [Glucose](https://one-course.com/books/biology/1/en/chapter/49-organs-at-work#prop-g7-organs-at-work-bill) then piles up after meals, overwhelms the [kidney](https://one-course.com/books/biology/1/en/chapter/53-removing-the-wastes#def-g7-removing-wastes-kidneys)’s reclaiming, and appears in the [urine](https://one-course.com/books/biology/1/en/chapter/53-removing-the-wastes#def-g7-removing-wastes-kidneys).

**Exercise 61.6 ★.**

Where do the nervous and hormonal systems interface? Give one example of a relay.

**Solution of Exercise 61.6.**

At the [brain](https://one-course.com/books/biology/1/en/chapter/33-the-brain-in-command#def-g5-brain-in-command-system)’s base — the control [gland](#def-g8-hormonal-communication-glands), [nervous system](https://one-course.com/books/biology/1/en/chapter/33-the-brain-in-command#def-g5-brain-in-command-system) above, [hormones](#def-g8-hormonal-communication-glands) below. Example: the fright — [nerve](https://one-course.com/books/biology/1/en/chapter/60-nervous-communication#def-g8-nervous-communication-neuron) signals first, the adrenal letter sustaining the alert; or day-length turning into the sheep’s breeding [hormones](#def-g8-hormonal-communication-glands).

**Exercise 61.7 ★★.**

Why is a thermostat the right image for [feedback](#prop-g8-hormonal-communication-feedback), and a tap the wrong one?

**Solution of Exercise 61.7.**

A tap pours until someone turns it; a thermostat measures what it is changing and adjusts itself. The [gland](#def-g8-hormonal-communication-glands) reads the level it regulates — secretion rises and subsides with the need, no external hand required.

**Exercise 61.8 ★★.**

Run [Method 61.7](#met-g8-hormonal-communication-read) on the pancreas’s storage [hormone](#def-g8-hormonal-communication-glands).

**Solution of Exercise 61.8.**

Writer: the pancreas, triggered by rising [blood](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#prop-g4-journey-of-food-absorb) [glucose](https://one-course.com/books/biology/1/en/chapter/49-organs-at-work#prop-g7-organs-at-work-bill). Receivers: [liver](https://one-course.com/books/biology/1/en/chapter/50-digestion-and-nutrients#prop-g7-digestion-and-nutrients-absorption) and [muscles](https://one-course.com/books/biology/1/en/chapter/17-bones-and-muscles#def-g3-bones-and-muscles-muscle) above all — they bank the surplus on delivery. [Feedback](#prop-g8-hormonal-communication-feedback): the falling level itself subsides the secretion. Failure and use: [diabetes](#ex-g8-hormonal-communication-diabetes) — and medicine’s measured doses, the letter by syringe.

**Exercise 61.9 ★★.**

Explain the diabetic’s syringe and the [contraceptive pill](https://one-course.com/books/biology/1/en/chapter/59-contraception#def-g8-contraception-pill) as the same kind of act, by question 4 of the method.

**Solution of Exercise 61.9.**

Both write a body-letter by hand: the syringe supplies the pancreas’s missing storage message at mealtimes; the pill supplies the cycle’s “suspended” message daily. Same act — imitating a [hormone](#def-g8-hormonal-communication-glands) to run its system on purpose — one restoring a failed correspondence, one overriding a healthy one by choice.

**Exercise 61.10 ★★.**

Assign systems, with reasons: shivering’s start; the growth of a beard; [blood](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#prop-g4-journey-of-food-absorb) [glucose](https://one-course.com/books/biology/1/en/chapter/49-organs-at-work#prop-g7-organs-at-work-bill)’s narrow lane; the knee-jerk.

**Solution of Exercise 61.10.**

Shivering’s start: nervous — split-second [muscle](https://one-course.com/books/biology/1/en/chapter/17-bones-and-muscles#def-g3-bones-and-muscles-muscle) orders. The beard: hormonal — months, body-wide, bloodstream. The [glucose](https://one-course.com/books/biology/1/en/chapter/49-organs-at-work#prop-g7-organs-at-work-bill) lane: hormonal — [feedback](#prop-g8-hormonal-communication-feedback) correspondence. The knee-jerk: nervous — one junction, a fiftieth of a second.

**Exercise 61.11 ★★.**

The sheep of [Example 55.2](https://one-course.com/books/biology/1/en/chapter/55-reproduction-and-the-environment#ex-g8-reproduction-and-environment-lambs) turn [light](https://one-course.com/books/biology/1/en/chapter/37-exploring-our-environment#def-g6-exploring-our-environment-conditions) into lambs. Trace the relay through [Remark 61.6](#rem-g8-hormonal-communication-partnership)’s offices.

**Solution of Exercise 61.11.**

The [eyes](https://one-course.com/books/biology/1/en/chapter/5-the-five-senses#def-g1-the-five-senses-sense)’ perception of shortening days is nervous; the brain-base office translates it, conducting the control [gland](#def-g8-hormonal-communication-glands); its letters wake the [ovaries](https://one-course.com/books/biology/1/en/chapter/57-the-reproductive-systems#def-g8-reproductive-systems-female)’ own [hormone](#def-g8-hormonal-communication-glands) program; the ewes’ cycles start — [light](https://one-course.com/books/biology/1/en/chapter/37-exploring-our-environment#def-g6-exploring-our-environment-conditions) in at the telegraph, lambs out by post.

**Exercise 61.12 ★★★.**

“Receptors make a broadcast into a network of private lines.” Defend the sentence, then push it: what must change in a [cell](https://one-course.com/books/biology/1/en/chapter/29-a-first-look-at-cells#def-g5-first-look-at-cells-cell) for it to *join* a [hormone](#def-g8-hormonal-communication-glands)’s audience — and what does that suggest about how [puberty](https://one-course.com/books/biology/1/en/chapter/56-puberty#def-g8-puberty-puberty)’s targets came to be listening?

**Solution of Exercise 61.12.**

Defense: one [blood](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#prop-g4-journey-of-food-absorb) carries every letter, yet each acts only where receptors answer — the audience defines the channel, so broadcast becomes private lines. The push: a [cell](https://one-course.com/books/biology/1/en/chapter/29-a-first-look-at-cells#def-g5-first-look-at-cells-cell) joins an audience by building the receptor — so which tissues listen is itself built, organ by organ, during development; [puberty](https://one-course.com/books/biology/1/en/chapter/56-puberty#def-g8-puberty-puberty)’s targets — voice box, [skin](https://one-course.com/books/biology/1/en/chapter/5-the-five-senses#def-g1-the-five-senses-sense), growth plates — were fitted with their receivers in advance, waiting years for the first letter.

## 61.5 Problem: The Glucose Logbook

**Problem 61.1.**

Weekend problem — a day of blood sugar, read as correspondence

A continuous [glucose](https://one-course.com/books/biology/1/en/chapter/49-organs-at-work#prop-g7-organs-at-work-bill) monitor’s (invented) day-log: steady overnight; breakfast at 8 — a rise, then a calm descent by 10; sport at 12 — a brief dip, quickly caught; a missed lunch — steady all afternoon regardless; a fright at 17 (a near-miss on the bicycle) — a sharp brief rise; supper at 19 — rise and descent again.

**Part I — The morning.**

1. Overnight steadiness: which two-letter correspondence held the lane while its owner slept?
2. Breakfast’s rise and descent: name the trigger, the writer, the letter, and the receivers that banked the surplus.
3. Why is the descent’s *stopping* — no plunge below the lane — itself [feedback](#prop-g8-hormonal-communication-feedback) ’s signature?
4. The 10 o’clock level matches the 7 o’clock one. What does the thermostat image predict about the secretion’s course between?

**Part II — The afternoon.**

5. Sport’s dip and catch: which letter called the [liver](https://one-course.com/books/biology/1/en/chapter/50-digestion-and-nutrients#prop-g7-digestion-and-nutrients-absorption) ’s bank, and which chapter’s account was being spent?
6. The missed lunch changed nothing visible. Which [partner-hormone](#def-g8-hormonal-communication-glands) ’s quiet work bridged the afternoon?
7. The fright’s sharp rise: name the writer and the point of the sudden sugar — ready for what, by [Example 61.3](#ex-g8-hormonal-communication-alarm) ?
8. Why did the fright’s rise subside within the hour, unlike [diabetes](#ex-g8-hormonal-communication-diabetes) ’s lasting pile-up?

**Part III — The consultation.**

9. A diabetic’s log of the same day would differ at every meal. Describe breakfast’s curve untreated, and where the [kidney](https://one-course.com/books/biology/1/en/chapter/53-removing-the-wastes#def-g7-removing-wastes-kidneys) ’s signal would appear.
10. The treated version: what does the measured dose before each meal imitate, and why must its size match the plate?
11. The doctor calls the healthy log “a conversation you never hear”. List the speakers of the day — [glands](#def-g8-hormonal-communication-glands) , letters, receivers — in one summary table or paragraph.
12. Close with the chapter’s moral in a sentence: what kind of system keeps a value in a lane for a lifetime without a driver?

**Solution of Problem 61.1.**

**1.** The pancreas’s paired letters — storage [hormone](#def-g8-hormonal-communication-glands) on the rise, its releasing partner on the fall — holding the lane by [feedback](#prop-g8-hormonal-communication-feedback) while the owner slept.

**2.** Trigger: the meal’s [glucose](https://one-course.com/books/biology/1/en/chapter/49-organs-at-work#prop-g7-organs-at-work-bill) crossing the [villi](https://one-course.com/books/biology/1/en/chapter/50-digestion-and-nutrients#prop-g7-digestion-and-nutrients-absorption) and lifting the [blood](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#prop-g4-journey-of-food-absorb) level. Writer: the pancreas. Letter: the storage [hormone](#def-g8-hormonal-communication-glands). Receivers: [liver](https://one-course.com/books/biology/1/en/chapter/50-digestion-and-nutrients#prop-g7-digestion-and-nutrients-absorption) and [muscles](https://one-course.com/books/biology/1/en/chapter/17-bones-and-muscles#def-g3-bones-and-muscles-muscle), banking the surplus.

**3.** A tap would pour past the goal into a plunge; the descent leveling into the lane shows the secretion subsiding as its own result arrives — self-measuring, self-stopping.

**4.** That it rose with the level and died back with it: a curve of secretion shadowing the curve of [glucose](https://one-course.com/books/biology/1/en/chapter/49-organs-at-work#prop-g7-organs-at-work-bill), peak trailing peak — the thermostat’s course.

**5.** The releasing partner (with the alarm [hormone](#def-g8-hormonal-communication-glands)’s help in hard effort): the [liver](https://one-course.com/books/biology/1/en/chapter/50-digestion-and-nutrients#prop-g7-digestion-and-nutrients-absorption)’s banked [glucose](https://one-course.com/books/biology/1/en/chapter/49-organs-at-work#prop-g7-organs-at-work-bill) — the bank filled at breakfast in [Example 50.9](https://one-course.com/books/biology/1/en/chapter/50-digestion-and-nutrients#ex-g7-digestion-and-nutrients-breadtrace)’s manner — spent into the working [muscles](https://one-course.com/books/biology/1/en/chapter/17-bones-and-muscles#def-g3-bones-and-muscles-muscle)’ bill.

**6.** The same releasing partner: steadily unlocking the bank through the foodless hours, matching the body’s spending — the lane held from the other side.

**7.** The adrenal [glands](#def-g8-hormonal-communication-glands). The sugar readies fuel for *flight or fight*: the alarm letter’s whole point is a body stocked and rerouted for immediate effort — whether or not the effort comes.

**8.** Because the healthy correspondence answered it: the released surplus, unspent (the near-miss passed), triggered the storage letter in its turn, and the lane was restored — alarm and thermostat in sequence.

**9.** Untreated: breakfast’s rise climbing on, undescending — no storage letter written or heard — a high plateau through the morning; past the reclaiming threshold, sugar appears in the [urine](https://one-course.com/books/biology/1/en/chapter/53-removing-the-wastes#def-g7-removing-wastes-kidneys) ([Example 53.5](https://one-course.com/books/biology/1/en/chapter/53-removing-the-wastes#ex-g7-removing-wastes-thrift)’s signal).

**10.** The pancreas’s own mealtime letter. The dose must match the plate because the letter’s size must match the [glucose](https://one-course.com/books/biology/1/en/chapter/49-organs-at-work#prop-g7-organs-at-work-bill) it is to bank — too small [leaves](https://one-course.com/books/biology/1/en/chapter/3-plants-around-us#def-g1-plants-around-us-parts) a pile-up, too large overshoots the lane downward, which is its own emergency.

**11.** Overnight and afternoon: pancreas’s pair, [liver](https://one-course.com/books/biology/1/en/chapter/50-digestion-and-nutrients#prop-g7-digestion-and-nutrients-absorption) and [muscles](https://one-course.com/books/biology/1/en/chapter/17-bones-and-muscles#def-g3-bones-and-muscles-muscle) answering — the lane held. Morning and evening meals: [glucose](https://one-course.com/books/biology/1/en/chapter/49-organs-at-work#prop-g7-organs-at-work-bill) speaks, pancreas writes, [liver](https://one-course.com/books/biology/1/en/chapter/50-digestion-and-nutrients#prop-g7-digestion-and-nutrients-absorption) banks. Noon: effort spends, the releasing partner unlocks. Five o’clock: adrenals interject, pancreas tidies after. One value, five speakers, no silence all day.

**12.** “A [feedback](#prop-g8-hormonal-communication-feedback) system: writers that read the results of their own letters — which is how a value rides a narrow lane for a lifetime with nobody driving.”