---
title: "Blood Glucose and Diabetes"
book: "High School Biology"
subject: biology
language: en
chapter: 32
exercises: 15
source: https://one-course.com/books/biology/2/en/chapter/32-blood-glucose-and-diabetes
---

# Chapter 32 — Blood Glucose and Diabetes

Five litres of blood, one gram of glucose in each: five grams in all, about a sugar lump. The brain alone burns that amount every hour, day and night, and cannot use anything else. Yet a person who eats nothing for a day, or eats a whole cake at once, keeps the concentration within a few tenths of a gram per litre of the same value — and a person whose pancreas has failed does not, with consequences from thirst to coma. This chapter is about the most closely watched number in the body, the organs that hold it steady, and what happens, in the two forms of [diabetes](#def-g12-glucose-and-diabetes-diabetes), when they cannot.

## 32.1 A regulated constant

**Definition 32.1 (Glycaemia).**

The *glycaemia* is the concentration of glucose in the blood plasma: about $1\,\mathrm{g}/\mathrm{L}$ ($5.5\,\mathrm{mmol}/\mathrm{L}$) before a meal in a healthy person, rising to $1.4\,\mathrm{g}/\mathrm{L}$ within an hour of eating and returning within two, falling to $0.7\,\mathrm{g}/\mathrm{L}$ after a day’s fast. Below $0.5\,\mathrm{g}/\mathrm{L}$ the brain fails (confusion, then coma); above $1.8\,\mathrm{g}/\mathrm{L}$ glucose spills into the urine, and years above $1.3\,\mathrm{g}/\mathrm{L}$ damage vessels and nerves. Glycaemia is a *regulated* quantity: a value held near a set point by a system that measures it and corrects it.

**Proposition 32.2 (The glucose pool and its fluxes).**

The $5\,\mathrm{g}$ of glucose in the blood are a pool through which large flows pass. *Inputs*: the intestine after a meal (up to $100\,\mathrm{g}$ in an hour), and between meals the *liver*, which releases glucose from its stored *[glycogen](https://one-course.com/books/biology/2/en/chapter/7-exercise-and-the-bodys-energy-needs#def-g10-exercise-and-energy-glycogen)* ($100\,\mathrm{g}$, half a day’s supply) and makes new glucose from [amino acids](https://one-course.com/books/biology/2/en/chapter/1-the-chemical-makeup-of-living-things#def-g10-chemistry-of-life-families) and lactate. *Outputs*: the brain ($5\,\mathrm{g}/\mathrm{h}$, constant), muscles (from a few grams to $100\,\mathrm{g}/\mathrm{h}$ at work), other tissues, and storage as [glycogen](https://one-course.com/books/biology/2/en/chapter/7-exercise-and-the-bodys-energy-needs#def-g10-exercise-and-energy-glycogen) in the liver and muscles or as fat. A pool of $5\,\mathrm{g}$ fed and drained at tens of grams per hour is stable only because the flows are adjusted minute by minute.

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

![The glucose pool. Meals and the liver feed it; the brain, muscles and fat tissue drain it; the liver alone can work in both directions, storing after a meal and releasing between meals.](https://one-course.com/images/onecourse/chapters/biology-2/g12-glucose-and-diabetes/fig-e9047afbb793.svg)

*The glucose pool. Meals and the liver feed it; the brain, muscles and fat tissue drain it; the liver alone can work in both directions, storing after a meal and releasing between meals.*

**Example 32.3 (A day of glycaemia).**

Breakfast at 8: [glycaemia](#def-g12-glucose-and-diabetes-glycaemia) rises from $0.9$ to $1.3\,\mathrm{g}/\mathrm{L}$ by 9 and is back at $1.0$ by 10, the excess having gone into liver and muscle [glycogen](https://one-course.com/books/biology/2/en/chapter/7-exercise-and-the-bodys-energy-needs#def-g10-exercise-and-energy-glycogen). From 10 to 13 the liver releases [glycogen](https://one-course.com/books/biology/2/en/chapter/7-exercise-and-the-bodys-energy-needs#def-g10-exercise-and-energy-glycogen) and the level holds near $0.9$. A run at 17 draws $60\,\mathrm{g}$ into the muscles in an hour; the liver empties half its store to keep pace, and the level dips to $0.8$. Overnight, the liver makes new glucose from [amino acids](https://one-course.com/books/biology/2/en/chapter/1-the-chemical-makeup-of-living-things#def-g10-chemistry-of-life-families), and at 7 the level is $0.9\,\mathrm{g}/\mathrm{L}$. Three hundred grams have passed through a pool of five.

## 32.2 The pancreas holds the balance

**Proposition 32.4 (Two hormones from the islets).**

Scattered through the pancreas, among the [cells](https://one-course.com/books/biology/2/en/chapter/2-cells-the-common-unit-of-life#def-g10-cells-common-unit-cell) that make digestive [enzymes](https://one-course.com/books/biology/2/en/chapter/15-enzymes-and-the-phenotype#def-g11-enzymes-and-phenotype-enzyme), lie a million small clusters of [cells](https://one-course.com/books/biology/2/en/chapter/2-cells-the-common-unit-of-life#def-g10-cells-common-unit-cell), the *islets*. Their [cells](https://one-course.com/books/biology/2/en/chapter/2-cells-the-common-unit-of-life#def-g10-cells-common-unit-cell) measure the [glycaemia](#def-g12-glucose-and-diabetes-glycaemia) of the blood flowing past and secrete two [hormones](https://one-course.com/books/biology/2/en/chapter/20-hormonal-control-of-reproduction#def-g11-hormones-and-reproduction-hormone) into it:

- *insulin* , from the $\beta$ [cells](https://one-course.com/books/biology/2/en/chapter/2-cells-the-common-unit-of-life#def-g10-cells-common-unit-cell) , when the [glycaemia](#def-g12-glucose-and-diabetes-glycaemia) rises: it makes muscle and fat [cells](https://one-course.com/books/biology/2/en/chapter/2-cells-the-common-unit-of-life#def-g10-cells-common-unit-cell) take up glucose, and the liver and muscles store it as [glycogen](https://one-course.com/books/biology/2/en/chapter/7-exercise-and-the-bodys-energy-needs#def-g10-exercise-and-energy-glycogen) ; the [glycaemia](#def-g12-glucose-and-diabetes-glycaemia) falls;
- *glucagon* , from the $\alpha$ [cells](https://one-course.com/books/biology/2/en/chapter/2-cells-the-common-unit-of-life#def-g10-cells-common-unit-cell) , when it falls: it makes the liver break [glycogen](https://one-course.com/books/biology/2/en/chapter/7-exercise-and-the-bodys-energy-needs#def-g10-exercise-and-energy-glycogen) down and release glucose; the [glycaemia](#def-g12-glucose-and-diabetes-glycaemia) rises.

The two act on the same organs in opposite directions; their balance, reset every few minutes by the measured [glycaemia](#def-g12-glucose-and-diabetes-glycaemia), is the regulation. [Insulin](#prop-g12-glucose-and-diabetes-hormones) is the only [hormone](https://one-course.com/books/biology/2/en/chapter/20-hormonal-control-of-reproduction#def-g11-hormones-and-reproduction-hormone) that lowers the [glycaemia](#def-g12-glucose-and-diabetes-glycaemia); several raise it.

**Evidence.** Removing the pancreas of a dog (1889) makes it diabetic within a day: its [glycaemia](#def-g12-glucose-and-diabetes-glycaemia) triples and glucose appears in its urine; tying off the duct that carries the digestive [enzymes](https://one-course.com/books/biology/2/en/chapter/15-enzymes-and-the-phenotype#def-g11-enzymes-and-phenotype-enzyme) does not, so the effect is not digestive. Injecting an extract of the [islets](#prop-g12-glucose-and-diabetes-hormones) (1921) lowers the [glycaemia](#def-g12-glucose-and-diabetes-glycaemia) of a diabetic dog, and of a diabetic child, within hours; the active substance, [insulin](#prop-g12-glucose-and-diabetes-hormones), was purified the same year. Isolated [islets](#prop-g12-glucose-and-diabetes-hormones) in a dish secrete [insulin](#prop-g12-glucose-and-diabetes-hormones) when the glucose of the medium is raised and [glucagon](#prop-g12-glucose-and-diabetes-hormones) when it is lowered. Injected [glucagon](#prop-g12-glucose-and-diabetes-hormones) raises the [glycaemia](#def-g12-glucose-and-diabetes-glycaemia) of a fasting person within minutes, and only if the liver holds [glycogen](https://one-course.com/books/biology/2/en/chapter/7-exercise-and-the-bodys-energy-needs#def-g10-exercise-and-energy-glycogen). ∎

![A section of pancreas: an islet, paler, among the darker clusters of enzyme-secreting cells. The islet’s cells read the blood’s glucose and answer with insulin or glucagon; the rest of the organ makes digestive juice.](https://one-course.com/images/onecourse/chapters/biology-2/g12-glucose-and-diabetes/img-a4615181f0e1.jpg)

*A section of pancreas: an islet, paler, among the darker clusters of enzyme-secreting [cells](https://one-course.com/books/biology/2/en/chapter/2-cells-the-common-unit-of-life#def-g10-cells-common-unit-cell). The islet’s [cells](https://one-course.com/books/biology/2/en/chapter/2-cells-the-common-unit-of-life#def-g10-cells-common-unit-cell) read the blood’s glucose and answer with [insulin](#prop-g12-glucose-and-diabetes-hormones) or [glucagon](#prop-g12-glucose-and-diabetes-hormones); the rest of the organ makes digestive juice.*

![The regulation of glycaemia. A rise triggers insulin, which makes the tissues store glucose and brings the level down; a fall triggers glucagon, which makes the liver release glucose and brings it up. Each hormone’s effect removes the signal that called it: two negative feedback loops around one set point.](https://one-course.com/images/onecourse/chapters/biology-2/g12-glucose-and-diabetes/fig-6ee5713a6966.svg)

*The regulation of [glycaemia](#def-g12-glucose-and-diabetes-glycaemia). A rise triggers [insulin](#prop-g12-glucose-and-diabetes-hormones), which makes the tissues store glucose and brings the level down; a fall triggers [glucagon](#prop-g12-glucose-and-diabetes-hormones), which makes the liver release glucose and brings it up. Each [hormone](https://one-course.com/books/biology/2/en/chapter/20-hormonal-control-of-reproduction#def-g11-hormones-and-reproduction-hormone)’s effect removes the signal that called it: two negative [feedback](https://one-course.com/books/biology/2/en/chapter/20-hormonal-control-of-reproduction#def-g11-hormones-and-reproduction-hormone) loops around one set point.*

**Example 32.5 (The loop in action).**

After a meal the [glycaemia](#def-g12-glucose-and-diabetes-glycaemia) climbs; within minutes the $\beta$ [cells](https://one-course.com/books/biology/2/en/chapter/2-cells-the-common-unit-of-life#def-g10-cells-common-unit-cell) release [insulin](#prop-g12-glucose-and-diabetes-hormones), the muscles and fat [cells](https://one-course.com/books/biology/2/en/chapter/2-cells-the-common-unit-of-life#def-g10-cells-common-unit-cell) open their glucose transporters, the liver switches to making [glycogen](https://one-course.com/books/biology/2/en/chapter/7-exercise-and-the-bodys-energy-needs#def-g10-exercise-and-energy-glycogen), and the level falls back — at which point [insulin](#prop-g12-glucose-and-diabetes-hormones) secretion falls too. Between meals the drift downward is met by [glucagon](#prop-g12-glucose-and-diabetes-hormones), [glycogen](https://one-course.com/books/biology/2/en/chapter/7-exercise-and-the-bodys-energy-needs#def-g10-exercise-and-energy-glycogen) is broken down, and the level holds. Neither [hormone](https://one-course.com/books/biology/2/en/chapter/20-hormonal-control-of-reproduction#def-g11-hormones-and-reproduction-hormone) is ever absent; their ratio moves, and the [glycaemia](#def-g12-glucose-and-diabetes-glycaemia) follows it within a narrow band.

## 32.3 When the loop fails: diabetes

**Definition 32.6 (Diabetes).**

*Diabetes* is a chronic excess of [glycaemia](#def-g12-glucose-and-diabetes-glycaemia): above $1.26\,\mathrm{g}/\mathrm{L}$ fasting, or above $2\,\mathrm{g}/\mathrm{L}$ two hours after a standard glucose load. Its early signs follow from the excess: glucose in the urine, which drags water with it (abundant urine, thirst), and weight loss when [cells](https://one-course.com/books/biology/2/en/chapter/2-cells-the-common-unit-of-life#def-g10-cells-common-unit-cell) cannot use the glucose around them. Its late damage — to the small vessels of the eye and kidney, to nerves, to the arteries — comes from years of glucose reacting with [proteins](https://one-course.com/books/biology/2/en/chapter/14-from-gene-to-protein#def-g11-gene-expression-protein). Two diseases share the name.

**Proposition 32.7 (Type 1 and type 2).**

- *Type 1 [diabetes](#def-g12-glucose-and-diabetes-diabetes)* (about 10% of cases) is the destruction of the $\beta$ [cells](https://one-course.com/books/biology/2/en/chapter/2-cells-the-common-unit-of-life#def-g10-cells-common-unit-cell) by the patient’s own immune system, usually in childhood or youth: [insulin](#prop-g12-glucose-and-diabetes-hormones) is absent. The [glycaemia](#def-g12-glucose-and-diabetes-glycaemia) rises unchecked, fat is burned for lack of usable glucose and its acid products accumulate; without injected [insulin](#prop-g12-glucose-and-diabetes-hormones) the disease is fatal within months. Treatment is [insulin](#prop-g12-glucose-and-diabetes-hormones) , several times a day, dosed to the meals and the measured [glycaemia](#def-g12-glucose-and-diabetes-glycaemia) , for life.
- *Type 2 [diabetes](#def-g12-glucose-and-diabetes-diabetes)* (about 90%) develops in adults, most often overweight and inactive: the tissues respond less and less to [insulin](#prop-g12-glucose-and-diabetes-hormones) ( *[insulin](#prop-g12-glucose-and-diabetes-hormones) resistance* ), the $\beta$ [cells](https://one-course.com/books/biology/2/en/chapter/2-cells-the-common-unit-of-life#def-g10-cells-common-unit-cell) compensate by secreting more, and after years they become exhausted. [Insulin](#prop-g12-glucose-and-diabetes-hormones) is present but insufficient. The predisposition is partly genetic ( [Chapter 16](https://one-course.com/books/biology/2/en/chapter/16-genetic-variation-and-disease#ch-g11-genes-and-disease) ); the trigger is the way of life, and the first treatment is its change — weight loss and exercise — before drugs and, late, [insulin](#prop-g12-glucose-and-diabetes-hormones) .

**Evidence.** Type 1 patients have antibodies against their own islet [cells](https://one-course.com/books/biology/2/en/chapter/2-cells-the-common-unit-of-life#def-g10-cells-common-unit-cell) years before symptoms, and at diagnosis their [islets](#prop-g12-glucose-and-diabetes-hormones) are almost empty of $\beta$ [cells](https://one-course.com/books/biology/2/en/chapter/2-cells-the-common-unit-of-life#def-g10-cells-common-unit-cell) and infiltrated by white [cells](https://one-course.com/books/biology/2/en/chapter/2-cells-the-common-unit-of-life#def-g10-cells-common-unit-cell); their blood [insulin](#prop-g12-glucose-and-diabetes-hormones) is undetectable and they respond to injected [insulin](#prop-g12-glucose-and-diabetes-hormones) at once. Type 2 patients have normal or high [insulin](#prop-g12-glucose-and-diabetes-hormones) at diagnosis; their muscle and fat [cells](https://one-course.com/books/biology/2/en/chapter/2-cells-the-common-unit-of-life#def-g10-cells-common-unit-cell) take up less glucose for a given [insulin](#prop-g12-glucose-and-diabetes-hormones) dose than a healthy person’s; identical twins share the disease in 70% of cases, and weight loss or a walking programme alone restores normal [glycaemia](#def-g12-glucose-and-diabetes-glycaemia) in many early cases. ∎

![The glucose tolerance test: glycaemia after a standard drink of 75\, g of glucose. A healthy person is back near 1\, g/ L in two hours; a diabetic starts high, climbs above 2\, g/ L and stays there. The intermediate curve is the warning stage, usually reversible.](https://one-course.com/images/onecourse/chapters/biology-2/g12-glucose-and-diabetes/fig-e22f609e12e0.svg)

*The glucose tolerance test: [glycaemia](#def-g12-glucose-and-diabetes-glycaemia) after a standard drink of $75\,\mathrm{g}$ of glucose. A healthy person is back near $1\,\mathrm{g}/\mathrm{L}$ in two hours; a diabetic starts high, climbs above $2\,\mathrm{g}/\mathrm{L}$ and stays there. The intermediate curve is the warning stage, usually reversible.*

**Example 32.8 (Managing a day with type 1).**

A teenager with type 1 measures her [glycaemia](#def-g12-glucose-and-diabetes-glycaemia) before each meal with a drop of blood, counts the [carbohydrate](https://one-course.com/books/biology/2/en/chapter/1-the-chemical-makeup-of-living-things#def-g10-chemistry-of-life-families) on her plate, and injects a dose of fast [insulin](#prop-g12-glucose-and-diabetes-hormones) proportional to it — about one unit per $10\,\mathrm{g}$ — plus a slow [insulin](#prop-g12-glucose-and-diabetes-hormones) once a day for the background. Too much [insulin](#prop-g12-glucose-and-diabetes-hormones), or a missed meal, and the level falls below $0.6\,\mathrm{g}/\mathrm{L}$: sweating, trembling, confusion, corrected by sugar in minutes. Too little, and the level stays above $2\,\mathrm{g}/\mathrm{L}$ with thirst and fatigue, and the vessels take the damage silently. She is doing, by hand, what her $\beta$ [cells](https://one-course.com/books/biology/2/en/chapter/2-cells-the-common-unit-of-life#def-g10-cells-common-unit-cell) did by [feedback](https://one-course.com/books/biology/2/en/chapter/20-hormonal-control-of-reproduction#def-g11-hormones-and-reproduction-hormone).

![The tools of a type 1 diabetic: a meter that reads the glycaemia from a drop of blood, and a pen that injects a measured dose of insulin. The loop of the islets, run by hand several times a day.](https://one-course.com/images/onecourse/chapters/biology-2/g12-glucose-and-diabetes/img-1260cfe67a3c.jpg)

*The tools of a type 1 diabetic: a meter that reads the [glycaemia](#def-g12-glucose-and-diabetes-glycaemia) from a drop of blood, and a pen that injects a measured dose of [insulin](#prop-g12-glucose-and-diabetes-hormones). The loop of the [islets](#prop-g12-glucose-and-diabetes-hormones), run by hand several times a day.*

**Method 32.9 (Reading a glycaemia record).**

1. Locate the set point and the band: fasting $0.7\text{ to }1.1\,\mathrm{g}/\mathrm{L}$ , after meals below $1.4$ ; two hours after a glucose load below $1.4$ (healthy), $1.4\text{ to }2\,$ (impaired), above $2\,\mathrm{g}/\mathrm{L}$ ( [diabetes](#def-g12-glucose-and-diabetes-diabetes) ).
2. For each rise, ask what put glucose in (meal, liver) and what should take it out ( [insulin](#prop-g12-glucose-and-diabetes-hormones) ’s targets); for each fall, what took it out (brain, muscle) and what should put it back ( [glucagon](#prop-g12-glucose-and-diabetes-hormones) , the liver).
3. Read the [hormones](https://one-course.com/books/biology/2/en/chapter/20-hormonal-control-of-reproduction#def-g11-hormones-and-reproduction-hormone) with the glucose: [insulin](#prop-g12-glucose-and-diabetes-hormones) should rise with the [glycaemia](#def-g12-glucose-and-diabetes-glycaemia) and [glucagon](#prop-g12-glucose-and-diabetes-hormones) fall; absent [insulin](#prop-g12-glucose-and-diabetes-hormones) means type 1, high [insulin](#prop-g12-glucose-and-diabetes-hormones) with high [glycaemia](#def-g12-glucose-and-diabetes-glycaemia) means resistance.
4. Convert units when needed: $1\,\mathrm{g}/\mathrm{L}$ of glucose is $5.55\,\mathrm{mmol}/\mathrm{L}$ .

**Remark 32.10 (A model of regulation).**

Sensor, set point, two opposed effectors, negative [feedback](https://one-course.com/books/biology/2/en/chapter/20-hormonal-control-of-reproduction#def-g11-hormones-and-reproduction-hormone): the control of [glycaemia](#def-g12-glucose-and-diabetes-glycaemia) is the same design as the control of testosterone in [Chapter 20](https://one-course.com/books/biology/2/en/chapter/20-hormonal-control-of-reproduction#ch-g11-hormones-and-reproduction), and the design of most of the body’s constants — temperature, water, blood pressure, acidity. [Diabetes](#def-g12-glucose-and-diabetes-diabetes) is what a regulated constant looks like when its loop is broken: the value still responds to inputs, but nothing brings it back. Reading the curves of this chapter is practice for reading any of them.

## 32.4 Exercises

**Exercise 32.1 ★.**

Give the normal fasting [glycaemia](#def-g12-glucose-and-diabetes-glycaemia) in $\mathrm{g}/\mathrm{L}$ and in $\mathrm{mmol}/\mathrm{L}$, and the two danger thresholds.

**Solution of Exercise 32.1.**

About $1\,\mathrm{g}/\mathrm{L}$, i.e. $5.5\,\mathrm{mmol}/\mathrm{L}$. Below $0.5\,\mathrm{g}/\mathrm{L}$ the brain fails; above $1.8\,\mathrm{g}/\mathrm{L}$ glucose passes into the urine (and years above $1.3\,\mathrm{g}/\mathrm{L}$ damage the vessels).

**Exercise 32.2 ★.**

Name the two [hormones](https://one-course.com/books/biology/2/en/chapter/20-hormonal-control-of-reproduction#def-g11-hormones-and-reproduction-hormone) of the [islets](#prop-g12-glucose-and-diabetes-hormones), the [cells](https://one-course.com/books/biology/2/en/chapter/2-cells-the-common-unit-of-life#def-g10-cells-common-unit-cell) that make them, and the effect of each on the [glycaemia](#def-g12-glucose-and-diabetes-glycaemia).

**Solution of Exercise 32.2.**

[Insulin](#prop-g12-glucose-and-diabetes-hormones), from the $\beta$ [cells](https://one-course.com/books/biology/2/en/chapter/2-cells-the-common-unit-of-life#def-g10-cells-common-unit-cell), lowers the [glycaemia](#def-g12-glucose-and-diabetes-glycaemia) (uptake and storage by muscle, fat and liver); [glucagon](#prop-g12-glucose-and-diabetes-hormones), from the $\alpha$ [cells](https://one-course.com/books/biology/2/en/chapter/2-cells-the-common-unit-of-life#def-g10-cells-common-unit-cell), raises it (release of glucose by the liver).

**Exercise 32.3 ★.**

Which organ can both store and release glucose? In what form does it store it?

**Solution of Exercise 32.3.**

The liver, as [glycogen](https://one-course.com/books/biology/2/en/chapter/7-exercise-and-the-bodys-energy-needs#def-g10-exercise-and-energy-glycogen) (and it can also make new glucose from [amino acids](https://one-course.com/books/biology/2/en/chapter/1-the-chemical-makeup-of-living-things#def-g10-chemistry-of-life-families) and lactate).

**Exercise 32.4 ★.**

State the essential difference between type 1 and type 2 [diabetes](#def-g12-glucose-and-diabetes-diabetes) in one sentence each.

**Solution of Exercise 32.4.**

Type 1: the $\beta$ [cells](https://one-course.com/books/biology/2/en/chapter/2-cells-the-common-unit-of-life#def-g10-cells-common-unit-cell) are destroyed and [insulin](#prop-g12-glucose-and-diabetes-hormones) is absent. Type 2: [insulin](#prop-g12-glucose-and-diabetes-hormones) is present but the tissues respond to it poorly, and the $\beta$ [cells](https://one-course.com/books/biology/2/en/chapter/2-cells-the-common-unit-of-life#def-g10-cells-common-unit-cell) eventually tire.

**Exercise 32.5 ★.**

From the tolerance-test figure, read the three curves at 120 minutes and classify each.

**Solution of Exercise 32.5.**

Healthy about $0.95\,\mathrm{g}/\mathrm{L}$; impaired tolerance about $1.7\,\mathrm{g}/\mathrm{L}$ (between 1.4 and 2); type 2 about $2.7\,\mathrm{g}/\mathrm{L}$ (above 2).

**Exercise 32.6 ★★.**

The brain uses $5\,\mathrm{g}$ of glucose per hour and the blood holds $5\,\mathrm{g}$. Explain why a person does not lose consciousness an hour after a meal, naming the organ and the [hormone](https://one-course.com/books/biology/2/en/chapter/20-hormonal-control-of-reproduction#def-g11-hormones-and-reproduction-hormone) responsible.

**Solution of Exercise 32.6.**

The liver releases glucose from its [glycogen](https://one-course.com/books/biology/2/en/chapter/7-exercise-and-the-bodys-energy-needs#def-g10-exercise-and-energy-glycogen) at the rate the brain removes it, under the control of [glucagon](#prop-g12-glucose-and-diabetes-hormones), so the pool stays near $5\,\mathrm{g}$ although its contents are renewed every hour.

**Exercise 32.7 ★★.**

Explain why removing the pancreas causes [diabetes](#def-g12-glucose-and-diabetes-diabetes) but tying its duct does not, and what this shows about where [insulin](#prop-g12-glucose-and-diabetes-hormones) is made and how it travels.

**Solution of Exercise 32.7.**

The duct carries digestive [enzymes](https://one-course.com/books/biology/2/en/chapter/15-enzymes-and-the-phenotype#def-g11-enzymes-and-phenotype-enzyme) to the gut; blocking it leaves [glycaemia](#def-g12-glucose-and-diabetes-glycaemia) normal, so the pancreas’s effect on glucose is not through digestion. Removing the whole organ removes the [islets](#prop-g12-glucose-and-diabetes-hormones): [insulin](#prop-g12-glucose-and-diabetes-hormones) is made in the pancreas and reaches its targets through the blood, not the duct.

**Exercise 32.8 ★★.**

A fasting person receives an injection of [glucagon](#prop-g12-glucose-and-diabetes-hormones): the [glycaemia](#def-g12-glucose-and-diabetes-glycaemia) rises by $0.4\,\mathrm{g}/\mathrm{L}$ in 20 minutes. The same injection after three days of fasting does nothing. Explain.

**Solution of Exercise 32.8.**

[Glucagon](#prop-g12-glucose-and-diabetes-hormones) acts by making the liver break down its [glycogen](https://one-course.com/books/biology/2/en/chapter/7-exercise-and-the-bodys-energy-needs#def-g10-exercise-and-energy-glycogen); after a night’s fast the store is there and the [glycaemia](#def-g12-glucose-and-diabetes-glycaemia) rises; after three days the [glycogen](https://one-course.com/books/biology/2/en/chapter/7-exercise-and-the-bodys-energy-needs#def-g10-exercise-and-energy-glycogen) is exhausted and [glucagon](#prop-g12-glucose-and-diabetes-hormones) has nothing to release.

**Exercise 32.9 ★★.**

Why does a diabetic pass abundant urine and feel thirsty?

**Solution of Exercise 32.9.**

Above about $1.8\,\mathrm{g}/\mathrm{L}$ the kidneys cannot reabsorb all the glucose they filter; it passes into the urine and, by osmosis, draws water with it. The water lost must be replaced: thirst.

**Exercise 32.10 ★★.**

A type 1 patient injects her usual dose of [insulin](#prop-g12-glucose-and-diabetes-hormones) and then skips lunch. Predict what happens over the next two hours and why.

**Solution of Exercise 32.10.**

The [insulin](#prop-g12-glucose-and-diabetes-hormones) drives glucose into the muscles and fat [cells](https://one-course.com/books/biology/2/en/chapter/2-cells-the-common-unit-of-life#def-g10-cells-common-unit-cell) and stops the liver’s release, but no glucose comes in: the [glycaemia](#def-g12-glucose-and-diabetes-glycaemia) falls below $0.6\,\mathrm{g}/\mathrm{L}$ within an hour or two, with sweating, trembling and confusion; sugar taken at once corrects it.

**Exercise 32.11 ★★.**

Explain why exercise lowers the [glycaemia](#def-g12-glucose-and-diabetes-glycaemia) of a type 2 diabetic even without any change in [insulin](#prop-g12-glucose-and-diabetes-hormones), using [Chapter 10](https://one-course.com/books/biology/2/en/chapter/10-physical-activity-and-health#ch-g10-sport-and-health).

**Solution of Exercise 32.11.**

A working muscle takes up glucose from the blood by a route that does not need [insulin](#prop-g12-glucose-and-diabetes-hormones), and trained muscle regains sensitivity to [insulin](#prop-g12-glucose-and-diabetes-hormones) between sessions; the [glycaemia](#def-g12-glucose-and-diabetes-glycaemia) falls during and after exercise, and the tissues’ resistance, the disease’s cause, is reduced.

**Exercise 32.12 ★★★.**

Two patients have a fasting [glycaemia](#def-g12-glucose-and-diabetes-glycaemia) of $2\,\mathrm{g}/\mathrm{L}$. One has no detectable [insulin](#prop-g12-glucose-and-diabetes-hormones); the other has three times the normal [insulin](#prop-g12-glucose-and-diabetes-hormones). Diagnose each, and say what each patient’s [islets](#prop-g12-glucose-and-diabetes-hormones) are doing.

**Solution of Exercise 32.12.**

No [insulin](#prop-g12-glucose-and-diabetes-hormones): type 1, the [islets](#prop-g12-glucose-and-diabetes-hormones)’ $\beta$ [cells](https://one-course.com/books/biology/2/en/chapter/2-cells-the-common-unit-of-life#def-g10-cells-common-unit-cell) are destroyed and secrete nothing. Three times normal [insulin](#prop-g12-glucose-and-diabetes-hormones): type 2, the [islets](#prop-g12-glucose-and-diabetes-hormones) are secreting at full stretch against tissues that no longer respond.

**Exercise 32.13 ★★★.**

Draw, or describe, the curves of [glycaemia](#def-g12-glucose-and-diabetes-glycaemia) and of [insulin](#prop-g12-glucose-and-diabetes-hormones) over the three hours after a meal in a healthy person, in a type 1 patient without treatment, and in a type 2 patient. Explain each difference.

**Solution of Exercise 32.13.**

Healthy: [glycaemia](#def-g12-glucose-and-diabetes-glycaemia) rises to about $1.3\,\mathrm{g}/\mathrm{L}$ at 30–60 minutes and returns by 2 hours; [insulin](#prop-g12-glucose-and-diabetes-hormones) rises with it and falls with it. Type 1 untreated: [glycaemia](#def-g12-glucose-and-diabetes-glycaemia) climbs above $2\,\mathrm{g}/\mathrm{L}$ and stays; [insulin](#prop-g12-glucose-and-diabetes-hormones) flat at zero — nothing removes the glucose. Type 2: [glycaemia](#def-g12-glucose-and-diabetes-glycaemia) rises high and falls slowly; [insulin](#prop-g12-glucose-and-diabetes-hormones) rises higher than normal and stays high — much [hormone](https://one-course.com/books/biology/2/en/chapter/20-hormonal-control-of-reproduction#def-g11-hormones-and-reproduction-hormone), little effect.

**Exercise 32.14 ★★★.**

A meal contains $80\,\mathrm{g}$ of [carbohydrate](https://one-course.com/books/biology/2/en/chapter/1-the-chemical-makeup-of-living-things#def-g10-chemistry-of-life-families). If all of it entered the blood at once, what would the [glycaemia](#def-g12-glucose-and-diabetes-glycaemia) become? Explain why it never does, listing the fates of the glucose in the first two hours.

**Solution of Exercise 32.14.**

$5 + 80 = 85\,\mathrm{g}$ in $5\,\mathrm{L}$: $17\,\mathrm{g}/\mathrm{L}$. It never does because absorption takes an hour or two, and as glucose arrives [insulin](#prop-g12-glucose-and-diabetes-hormones) sends it into liver [glycogen](https://one-course.com/books/biology/2/en/chapter/7-exercise-and-the-bodys-energy-needs#def-g10-exercise-and-energy-glycogen), muscle [glycogen](https://one-course.com/books/biology/2/en/chapter/7-exercise-and-the-bodys-energy-needs#def-g10-exercise-and-energy-glycogen) and fat, while the brain and tissues burn some: the pool never holds more than a few grams above normal.

**Exercise 32.15 ★★★.**

Compare the regulation of [glycaemia](#def-g12-glucose-and-diabetes-glycaemia) with that of testosterone in [Chapter 20](https://one-course.com/books/biology/2/en/chapter/20-hormonal-control-of-reproduction#ch-g11-hormones-and-reproduction): sensor, set point, effectors, sign of the [feedback](https://one-course.com/books/biology/2/en/chapter/20-hormonal-control-of-reproduction#def-g11-hormones-and-reproduction-hormone). What is special about having two opposed [hormones](https://one-course.com/books/biology/2/en/chapter/20-hormonal-control-of-reproduction#def-g11-hormones-and-reproduction-hormone)?

**Solution of Exercise 32.15.**

Both: a sensor (islet [cells](https://one-course.com/books/biology/2/en/chapter/2-cells-the-common-unit-of-life#def-g10-cells-common-unit-cell); hypothalamus and pituitary), a set point, effectors, and negative [feedback](https://one-course.com/books/biology/2/en/chapter/20-hormonal-control-of-reproduction#def-g11-hormones-and-reproduction-hormone) that removes the signal. [Glycaemia](#def-g12-glucose-and-diabetes-glycaemia) has two opposed [hormones](https://one-course.com/books/biology/2/en/chapter/20-hormonal-control-of-reproduction#def-g11-hormones-and-reproduction-hormone) acting on the same organs, so the variable can be pushed both up and down actively; testosterone’s loop has one [hormone](https://one-course.com/books/biology/2/en/chapter/20-hormonal-control-of-reproduction#def-g11-hormones-and-reproduction-hormone) and corrects mainly by more or less of it. Two opposed effectors give a faster, tighter control of a variable that changes quickly in both directions.

## 32.5 Problem: Five Grams of Sugar

**Problem 32.1.**

Weekend problem — the glucose of the blood accounted for over a day: the pool and its flows, a tolerance test read, an insulin dose computed, and a loop that has to be replaced by hand

Take a blood volume of $5\,\mathrm{L}$, a brain consumption of $5\,\mathrm{g}/\mathrm{h}$ of glucose, a liver [glycogen](https://one-course.com/books/biology/2/en/chapter/7-exercise-and-the-bodys-energy-needs#def-g10-exercise-and-energy-glycogen) store of $100\,\mathrm{g}$, and muscle [glycogen](https://one-course.com/books/biology/2/en/chapter/7-exercise-and-the-bodys-energy-needs#def-g10-exercise-and-energy-glycogen) of $400\,\mathrm{g}$. One unit of fast [insulin](#prop-g12-glucose-and-diabetes-hormones) disposes of about $10\,\mathrm{g}$ of [carbohydrate](https://one-course.com/books/biology/2/en/chapter/1-the-chemical-makeup-of-living-things#def-g10-chemistry-of-life-families).

**Part I — The pool.**

1. Compute the mass of glucose in the blood at $1\,\mathrm{g}/\mathrm{L}$ , and the same concentration in $\mathrm{mmol}/\mathrm{L}$ (glucose $180\,\mathrm{g}/\mathrm{mol}$ ).
2. How long would the blood’s glucose last the brain alone, if nothing replaced it?
3. Between meals, the liver replaces it. How long does the liver’s [glycogen](https://one-course.com/books/biology/2/en/chapter/7-exercise-and-the-bodys-energy-needs#def-g10-exercise-and-energy-glycogen) last the brain? What happens after that?
4. Muscle [glycogen](https://one-course.com/books/biology/2/en/chapter/7-exercise-and-the-bodys-energy-needs#def-g10-exercise-and-energy-glycogen) is four times the liver’s, but muscles cannot release glucose into the blood. Explain why muscle [glycogen](https://one-course.com/books/biology/2/en/chapter/7-exercise-and-the-bodys-energy-needs#def-g10-exercise-and-energy-glycogen) does not help the brain, and what it is for.
5. A meal delivers $60\,\mathrm{g}$ of glucose over an hour. If none were removed, what would the [glycaemia](#def-g12-glucose-and-diabetes-glycaemia) reach? What actually removes it, and where does it go?

**Part II — The test.** A patient drinks $75\,\mathrm{g}$ of glucose. Measured [glycaemia](#def-g12-glucose-and-diabetes-glycaemia) and [insulin](#prop-g12-glucose-and-diabetes-hormones):

| minutes | 0 | 30 | 60 | 90 | 120 | 180 |
| --- | --- | --- | --- | --- | --- | --- |
| [glycaemia](#def-g12-glucose-and-diabetes-glycaemia) (g/L) | 1.15 | 1.8 | 2.05 | 2.0 | 1.85 | 1.6 |
| [insulin](#prop-g12-glucose-and-diabetes-hormones) (% of a healthy peak) | 90 | 140 | 180 | 200 | 190 | 160 |

6. Classify the patient with the thresholds of [Method 32.9](#met-g12-glucose-and-diabetes-read) .
7. Is [insulin](#prop-g12-glucose-and-diabetes-hormones) lacking? What, then, is failing?
8. Name the disease, and give two features of the patient’s history you would expect.
9. What would the same table look like for a type 1 patient without treatment?
10. What is the first treatment prescribed, and by what mechanism does it act?

**Part III — Running the loop by hand.** A type 1 patient’s [glycaemia](#def-g12-glucose-and-diabetes-glycaemia) is $1.0\,\mathrm{g}/\mathrm{L}$ before dinner; the meal holds $90\,\mathrm{g}$ of [carbohydrate](https://one-course.com/books/biology/2/en/chapter/1-the-chemical-makeup-of-living-things#def-g10-chemistry-of-life-families).

11. Compute the dose of fast [insulin](#prop-g12-glucose-and-diabetes-hormones) for the meal.
12. She injects it but eats only half the meal. Estimate how far the [glycaemia](#def-g12-glucose-and-diabetes-glycaemia) may fall, and name the symptoms and the remedy.
13. She injects nothing and eats the whole meal. Estimate the [glycaemia](#def-g12-glucose-and-diabetes-glycaemia) if the $90\,\mathrm{g}$ all entered a $5\,\mathrm{L}$ pool, and say what the kidneys do above $1.8\,\mathrm{g}/\mathrm{L}$ .
14. Why must she also inject a slow [insulin](#prop-g12-glucose-and-diabetes-hormones) at night, when she eats nothing?
15. Explain in what sense the meter and the pen replace the $\beta$ [cell](https://one-course.com/books/biology/2/en/chapter/2-cells-the-common-unit-of-life#def-g10-cells-common-unit-cell) , and what they cannot replace.

**Part IV — The loop, reasoned.**

16. A drug stimulates the $\beta$ [cells](https://one-course.com/books/biology/2/en/chapter/2-cells-the-common-unit-of-life#def-g10-cells-common-unit-cell) to secrete more [insulin](#prop-g12-glucose-and-diabetes-hormones) . For which type of [diabetes](#def-g12-glucose-and-diabetes-diabetes) can it work, and why not for the other?
17. A person with type 2 loses $10\,\mathrm{kg}$ and walks an hour a day; six months later the tolerance test is normal. Explain which part of the loop was repaired.
18. Explain why a healthy person’s [insulin](#prop-g12-glucose-and-diabetes-hormones) and [glucagon](#prop-g12-glucose-and-diabetes-hormones) are never both high, and what an islet in a dish does when the glucose of the medium is set at $1\,\mathrm{g}/\mathrm{L}$ .
19. [Glucagon](#prop-g12-glucose-and-diabetes-hormones) , [adrenaline](https://one-course.com/books/biology/2/en/chapter/8-heart-and-lungs-during-effort#prop-g10-heart-lungs-effort-control) , cortisol and growth [hormone](https://one-course.com/books/biology/2/en/chapter/20-hormonal-control-of-reproduction#def-g11-hormones-and-reproduction-hormone) all raise the [glycaemia](#def-g12-glucose-and-diabetes-glycaemia) ; only [insulin](#prop-g12-glucose-and-diabetes-hormones) lowers it. Propose why the body has several safeguards against a low [glycaemia](#def-g12-glucose-and-diabetes-glycaemia) and one against a high one.
20. State the result: the glucose in the blood, the hours the liver can cover, the diagnosis of Part II, and the dose of Part III.

**Solution of Problem 32.1.**

**1.** $5\,\mathrm{g}$; $1\,\mathrm{g}/\mathrm{L} \div 180\,\mathrm{g}/\mathrm{mol} = 5.55\,\mathrm{mmol}/\mathrm{L}$.

**2.** One hour.

**3.** $100/5 = 20$ hours. After that the liver makes new glucose from [amino acids](https://one-course.com/books/biology/2/en/chapter/1-the-chemical-makeup-of-living-things#def-g10-chemistry-of-life-families) (and lactate), at the cost of the body’s [proteins](https://one-course.com/books/biology/2/en/chapter/14-from-gene-to-protein#def-g11-gene-expression-protein).

**4.** Muscle [cells](https://one-course.com/books/biology/2/en/chapter/2-cells-the-common-unit-of-life#def-g10-cells-common-unit-cell) lack the [enzyme](https://one-course.com/books/biology/2/en/chapter/15-enzymes-and-the-phenotype#def-g11-enzymes-and-phenotype-enzyme) that releases free glucose from [glycogen](https://one-course.com/books/biology/2/en/chapter/7-exercise-and-the-bodys-energy-needs#def-g10-exercise-and-energy-glycogen) into the blood; their [glycogen](https://one-course.com/books/biology/2/en/chapter/7-exercise-and-the-bodys-energy-needs#def-g10-exercise-and-energy-glycogen) is burned on the spot, for their own contraction.

**5.** $5 + 60 = 65\,\mathrm{g}$ in $5\,\mathrm{L}$: $13\,\mathrm{g}/\mathrm{L}$. [Insulin](#prop-g12-glucose-and-diabetes-hormones) sends the glucose into liver and muscle [glycogen](https://one-course.com/books/biology/2/en/chapter/7-exercise-and-the-bodys-energy-needs#def-g10-exercise-and-energy-glycogen) and into fat, and the tissues burn some; the [glycaemia](#def-g12-glucose-and-diabetes-glycaemia) peaks around $1.4\,\mathrm{g}/\mathrm{L}$.

**6.** Fasting $1.15\,\mathrm{g}/\mathrm{L}$ (below 1.26) but $1.85\,\mathrm{g}/\mathrm{L}$ at 120 minutes (between 1.4 and 2): impaired tolerance, at the threshold of [diabetes](#def-g12-glucose-and-diabetes-diabetes).

**7.** No: [insulin](#prop-g12-glucose-and-diabetes-hormones) is at twice a healthy peak. The tissues’ response to it is failing — [insulin](#prop-g12-glucose-and-diabetes-hormones) resistance.

**8.** Type 2 (or its warning stage). Expected: adult, overweight, inactive, often with diabetic relatives.

**9.** [Glycaemia](#def-g12-glucose-and-diabetes-glycaemia) starting above $1.5\,\mathrm{g}/\mathrm{L}$, rising above $2.5$ and not falling; [insulin](#prop-g12-glucose-and-diabetes-hormones) near zero throughout.

**10.** Weight loss and regular exercise: they restore the tissues’ sensitivity to [insulin](#prop-g12-glucose-and-diabetes-hormones) and let working muscle take up glucose without it.

**11.** $90/10 = 9$ units.

**12.** The dose disposes of $90\,\mathrm{g}$ but only $45\,\mathrm{g}$ arrive: the surplus [insulin](#prop-g12-glucose-and-diabetes-hormones) drives the [glycaemia](#def-g12-glucose-and-diabetes-glycaemia) down by the equivalent of $45\,\mathrm{g}$ in the pool and stores — well below $0.6\,\mathrm{g}/\mathrm{L}$: sweating, trembling, confusion; sugar at once.

**13.** $(5 + 90)/5 = 19\,\mathrm{g}/\mathrm{L}$ if nothing were removed; in reality several $\mathrm{g}/\mathrm{L}$. Above $1.8\,\mathrm{g}/\mathrm{L}$ the kidneys let glucose into the urine, with water: abundant urine and thirst.

**14.** Between meals the liver would otherwise release glucose unchecked ([glucagon](#prop-g12-glucose-and-diabetes-hormones) acts, nothing opposes it) and the tissues would burn fat with acid products: a background of [insulin](#prop-g12-glucose-and-diabetes-hormones) is needed for the basic balance, not only for meals.

**15.** The meter measures the [glycaemia](#def-g12-glucose-and-diabetes-glycaemia) as the $\beta$ [cell](https://one-course.com/books/biology/2/en/chapter/2-cells-the-common-unit-of-life#def-g10-cells-common-unit-cell) did; the pen delivers the [insulin](#prop-g12-glucose-and-diabetes-hormones) it would have secreted. They cannot replace the continuous, minute-by-minute adjustment: the patient measures a few times a day and estimates, where the [cell](https://one-course.com/books/biology/2/en/chapter/2-cells-the-common-unit-of-life#def-g10-cells-common-unit-cell) measured constantly and responded exactly.

**16.** Type 2, whose $\beta$ [cells](https://one-course.com/books/biology/2/en/chapter/2-cells-the-common-unit-of-life#def-g10-cells-common-unit-cell) exist and can be pushed. In type 1 there are no $\beta$ [cells](https://one-course.com/books/biology/2/en/chapter/2-cells-the-common-unit-of-life#def-g10-cells-common-unit-cell) to stimulate.

**17.** The tissues’ response to [insulin](#prop-g12-glucose-and-diabetes-hormones) — the effector side of the loop: with less fat and active muscle, a normal [insulin](#prop-g12-glucose-and-diabetes-hormones) signal again produces normal uptake, and the $\beta$ [cells](https://one-course.com/books/biology/2/en/chapter/2-cells-the-common-unit-of-life#def-g10-cells-common-unit-cell) are relieved.

**18.** Each is secreted in response to the opposite deviation of the same variable: a high [glycaemia](#def-g12-glucose-and-diabetes-glycaemia) calls [insulin](#prop-g12-glucose-and-diabetes-hormones) and silences [glucagon](#prop-g12-glucose-and-diabetes-hormones), a low one the reverse. At $1\,\mathrm{g}/\mathrm{L}$ the islet secretes both at a low, balanced rate — its resting state.

**19.** A low [glycaemia](#def-g12-glucose-and-diabetes-glycaemia) kills the brain within minutes, a high one damages slowly over years: the acute danger has several independent guards, the slow one a single one — which is why the failure of [insulin](#prop-g12-glucose-and-diabetes-hormones) alone is enough to cause a disease, and why [diabetes](#def-g12-glucose-and-diabetes-diabetes) is common.

**20.** About $5\,\mathrm{g}$ of glucose in the blood; the liver’s [glycogen](https://one-course.com/books/biology/2/en/chapter/7-exercise-and-the-bodys-energy-needs#def-g10-exercise-and-energy-glycogen) covers about 20 hours; the patient of Part II has impaired tolerance at the edge of type 2 [diabetes](#def-g12-glucose-and-diabetes-diabetes); the dose of Part III is 9 units.