Blood Glucose Regulation Simulator: Insulin, Glucagon and the Feedback Loop
Eat a meal and follow the glucose from the gut to the liver, muscles and brain while the pancreas answers with insulin, then fast, exercise or switch off the β-cells and watch glucagon and the liver fight back.
Pick a food: it goes to the stomach, then the small intestine absorbs it into the hepatic portal vein.
Working muscle takes up glucose without insulin, and the liver releases more to keep up.
An educational model, not medical advice: never use it to choose a real dose.
What's happening
Lab notebook
Every meal, injection, exercise and finger-prick reading is written here with the clock time. Export a CSV, or turn the session into a PDF lab report.
| # | Clock | What | Result |
|---|
Concept library
Predict first
Click "New problem" to begin.
Click "Start quiz" for 5 questions on the feedback loop, insulin and glucagon, the organs, diabetes and the numbers.
1 Overview
Simulate shows the body on the left: one loop of blood (the heart at the top) with the organs that add glucose (the gut through the hepatic portal vein, the liver) and take it away (brain, muscle, fat, liver, kidneys), and the pancreas whose islets sense it. In the middle is the feedback wheel around the glucose dial. On the right are the graphs, the cell close-ups and the glucose budget. Experiment has five practicals with a lab report; Quiz has practice questions and a 5-question quiz.
2 Running the body
- Press ▶ to run the clock (it starts at 07:00 after an overnight fast). Choose 1, 5 or 20 minutes of body time per second; ⏩ 2 h jumps ahead.
- In the Food panel pick something to eat or drink. In Activity start a walk, jog or run, or switch on stress. In Treatment inject rapid insulin, give glucagon, set a daily basal insulin or start metformin.
- The hexagons in the blood are glucose, the blue dots insulin, the orange triangles glucagon: their number follows the real concentration. The dots moving along each organ's branch show the size of its flow.
- ↺ starts again from the morning fast.
3 The feedback wheel
The top half is the insulin loop (glucose rises → β-cells release insulin → cells take up glucose and the liver stores glycogen → glucose falls back to normal); the bottom half is the glucagon loop (glucose falls → α-cells release glucagon → the liver releases glucose → glucose rises back to normal). The green dots are the set point. Each step lights up as the model does it, and a pulse runs along the loop that is working.
4 Graphs, cells and the budget
Graph plots glucose with the normal range, insulin and glucagon, or the glycogen stores; meals and injections are marked on the time axis. 📌 Keep curve leaves today's glucose faint on the graph to compare. Cells shows one cell of an organ (click an organ in the body to jump to it), with numbered steps that light when they happen. Budget shows every flow into and out of the blood right now.
5 The person
In the Body panel choose healthy, prediabetes, type 2 or type 1 diabetes, or set insulin sensitivity, β-cell function and α-cell response yourself. Changing the person starts a new morning. A type 1 person starts on 26 units of basal insulin a day.
6 Experiment mode and the lab report
Five labs: a glucose tolerance test on a mystery patient, insulin and glucagon fed and fasted, exercise after a meal, the glycemic index of three foods, and an insulin dose for type 1 diabetes. Each shows its aim, what you need and a safety note; the method ticks off as you work, and a conclusion question ends it. Then create a PDF lab report.
7 Quiz and units
The practice quiz covers the feedback loop, the hormones, the -genesis words, the organs, diabetes and the numbers, each with a worked solution. SI | US switches glucose between mmol/L and mg/dL and insulin between pmol/L and µIU/mL.
8 Keyboard
- Space runs or pauses the clock, F takes a finger-prick reading, N starts again, 1–3 pick Graph, Cells or Budget, S opens Status, Esc closes it. Right-click a view to save it as an image.
Blood glucose regulation: how insulin and glucagon keep blood sugar in balance
Blood glucose regulation is the way the body keeps the sugar in its blood within a narrow range, about 4 to 7.8 mmol/L, through the day: after a big meal, through the night and during a hard run. It is the textbook example of homeostasis by negative feedback. This free blood glucose regulation simulator lets you watch it happen: one model of the body (the gut, liver, pancreas, muscle, fat, brain and kidneys) drives every particle in the blood, every light on the feedback wheel and every point on the graphs.
- Organs
- Stomach and small intestine, hepatic portal vein, liver, pancreas and islets, muscle, fat, brain, kidneys
- Hormones
- Insulin and glucagon, with adrenaline and cortisol in stress and exercise
- People
- Healthy, prediabetes, type 2 and type 1 diabetes, or your own settings
- Modes
- Simulate, Experiment (5 practicals with a PDF report) and Quiz
- Price
- Free, no account or download; works on Chromebooks, tablets and phones
The negative feedback loop of blood glucose
Every feedback loop has a stimulus, a receptor, a control centre and effectors. For blood glucose the receptors and the control centre are the same cells, in the islets of Langerhans of the pancreas. A rise in glucose is sensed by the β-cells, which release insulin; the effectors (liver, muscle and fat) take glucose out of the blood, so it falls back. A fall is sensed by the α-cells, which release glucagon; the liver puts glucose back, so it rises. The response always opposes the change, which is what "negative" feedback means. In the simulator a 75 g glucose drink lifts a healthy person to about 8.6 mmol/L at 30 minutes and back to about 5.3 mmol/L by 2 hours.
How insulin lowers blood glucose
A β-cell takes in glucose through GLUT2 transporters and burns it, so its ATP rises. ATP closes the cell's K-ATP channels, the membrane depolarises, calcium floods in and the insulin granules fuse with the membrane: insulin follows glucose within minutes, with an extra early burst (the first phase) and a boost from gut hormones (incretins). Insulin binds receptors on its targets. In muscle and fat it moves GLUT4 transporters to the membrane, so glucose can enter; muscle takes about 80 % of the glucose cleared after a meal. In the liver it switches on glycogenesis (glucose stored as glycogen) and switches off the liver's own glucose release. Fat cells store fat and stop releasing fatty acids.
How glucagon raises blood glucose
Between meals the brain still burns about 120 g of glucose a day, and it cannot use fat. As glucose falls, insulin drops and the α-cells release glucagon. Glucagon acts mainly on the liver: it breaks glycogen down to glucose (glycogenolysis) and makes new glucose from lactate, amino acids and glycerol (gluconeogenesis). The liver can do this because it has the enzyme glucose-6-phosphatase; muscle cannot, so muscle glycogen only ever fuels the muscle itself. After about a day without food the liver's 100 g or so of glycogen is nearly gone and gluconeogenesis supplies almost all of the glucose. Adrenaline adds a fast push in exercise and stress, and cortisol a slow one.
Glucose, glycogen and glucagon: don't mix them up
| Word | What it is | Where |
|---|---|---|
| Glucose | The sugar in the blood, the cells' fuel | Blood and every cell |
| Glycogen | The storage carbohydrate: chains of glucose | Liver (≈ 100 g), muscle (≈ 400 g) |
| Glucagon | A hormone that raises blood glucose | Made by α-cells of the pancreas |
| Glycogenesis | Making glycogen from glucose (insulin) | Liver and muscle |
| Glycogenolysis | Breaking glycogen down to glucose (glucagon, adrenaline) | Liver (to the blood), muscle (for itself) |
| Gluconeogenesis | Making new glucose from non-carbohydrates (glucagon, cortisol) | Liver (and kidneys) |
Type 1 vs type 2 diabetes and the glucose tolerance test
In type 1 diabetes the β-cells are destroyed, so the insulin loop has no signal: glucose stays high, spills into the urine above the renal threshold (about 10 mmol/L), and fat is broken down into ketones. In type 2 diabetes insulin is still made but the effectors respond less (insulin resistance) and the β-cells cannot keep up. Doctors test the loop with an oral glucose tolerance test: 75 g of glucose after an overnight fast and a reading 2 hours later.
| Result (WHO / ADA) | Fasting glucose | 2 h after 75 g glucose | HbA1c |
|---|---|---|---|
| Normal | below 6.1 mmol/L (ADA: 5.6) | below 7.8 mmol/L | below 5.7 % |
| Prediabetes | 6.1–6.9 mmol/L (ADA: 5.6–6.9) | 7.8–11.0 mmol/L | 5.7–6.4 % |
| Diabetes | 7.0 mmol/L or more | 11.1 mmol/L or more | 6.5 % or more |
Experiments and course links
| Lab | What you find out | Course links |
|---|---|---|
| Glucose tolerance test | Normal, prediabetes or diabetes from your readings | AQA GCSE 4.5.3.3; A-level 3.6.4.2; IB D3.3 |
| Insulin and glucagon, fed and fasted | Which hormone rises when, and why | NGSS HS-LS1-3; AP Biology 4.5 |
| Exercise after a meal | Muscle uptake without insulin | GCSE homeostasis; A&P |
| Glycemic index | Why porridge rises more slowly than a glucose drink | Nutrition; IGCSE 0610 |
| Insulin dose in type 1 | Carbohydrate counting and hypoglycemia | Health science; A-level |
Who uses this blood glucose regulation simulator?
Middle and high school students learning homeostasis and negative feedback (NGSS, GCSE, IGCSE, A-level, IB, AP Biology), first-year anatomy and physiology and nursing students, and teachers who want a free, no-login model for a classroom screen or homework, with practicals and a lab report. It is an educational model with average parameters: it is not medical advice, and real people's glucose responses differ.
Frequently asked questions
How do insulin and glucagon regulate blood glucose?
They work as a pair in a negative feedback loop controlled by the islets of Langerhans in the pancreas. When blood glucose rises after a meal, β-cells release insulin, which makes muscle and fat cells take up glucose (through GLUT4 channels) and makes the liver store it as glycogen, so glucose falls back to normal. When blood glucose falls between meals or during exercise, α-cells release glucagon, which makes the liver break glycogen down (glycogenolysis) and make new glucose (gluconeogenesis), so glucose rises back to normal. Each hormone corrects a change in the opposite direction, which keeps fasting glucose at about 4 to 5.5 mmol/L (70 to 100 mg/dL).
What is the difference between glucose, glycogen and glucagon?
Glucose is the sugar carried in the blood and used by cells for energy. Glycogen is the storage form: thousands of glucose units joined in a branched chain, stored in the liver (about 100 g when full) and in muscle (about 400 g). Glucagon is a hormone, a small protein made by the α-cells of the pancreas, that tells the liver to break glycogen back down into glucose. The process words follow the same roots: glycogenesis makes glycogen, glycogenolysis breaks glycogen down, and gluconeogenesis makes new glucose from lactate, amino acids and glycerol.
What is the difference between type 1 and type 2 diabetes?
In type 1 diabetes the immune system destroys the β-cells, so the body makes almost no insulin; it usually starts in childhood or young adulthood and is treated with insulin injections or a pump for life. In type 2 diabetes the body still makes insulin, but muscle, fat and liver cells respond to it less (insulin resistance) and over the years the β-cells cannot keep up; it is linked to weight, inactivity and family history and is treated first with exercise, diet and tablets such as metformin. Both are diagnosed by a fasting glucose of 7.0 mmol/L (126 mg/dL) or more, a 2-hour glucose tolerance test of 11.1 mmol/L (200 mg/dL) or more, or an HbA1c of 6.5 % or more.
Explore related simulators
See every gland of the body and the thyroid's feedback loop in Hormone Quest: The Interactive Endocrine System Lab. Follow a meal's starch from the mouth to the small intestine with the Human Digestive System Simulator, and the glucose the kidneys filter and reabsorb in the Kidney Simulator. The Enzyme Kinetics Virtual Lab shows how amylase breaks starch into the sugars that reach the blood.
Sources: Hall & Hall, Guyton and Hall Textbook of Medical Physiology 14th edition, chapter 79; OpenStax Anatomy and Physiology 2e, section 17.9; OpenStax Biology 2e, section 37.3; Bergman et al., Am. J. Physiol. 236 (1979); Dalla Man, Rizza & Cobelli, IEEE Trans. Biomed. Eng. 54 (2007); WHO, Definition and diagnosis of diabetes mellitus and intermediate hyperglycaemia (2006); ADA Standards of Care in Diabetes, section 2; Nathan et al., Diabetes Care 31 (2008). An educational model: not medical advice.
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