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D3.3.3—Blood glucose regulation

Blood glucose is regulated by pancreatic alpha and beta cells secreting glucagon and insulin in opposing negative feedback responses in human physiology.

Syllabus
First assessment 2025
Objective
D3.3.3
Level
HL

Exam analysis

Chance of appearing7%of analysed past papers
Latest appearanceNovember 2025
Most common paperPaper2
Typical marks1–5

Common command terms

  • Identify
  • Explain
  • Describe
  • Outline
  • State
  • Discuss

Recent exam appearances

November 2025Paper2 ["HL"] · TZ19(b)[ 7 ]D3.3.3—Blood glucose regulation
May 2025Paper1A ["HL"] · TZ130[ 1 ]D3.3.3—Blood glucose regulation
November 2023Paper2 ["HL"] · TZ21(e)[ 3 ]D3.3.3—Blood glucose regulation
November 2017Paper1 ["HL"] · TZ025[ 1 ]D3.3.3—Blood glucose regulation
November 2015Paper2 ["HL"] · TZ08(b)[ 5 ]D3.3.3—Blood glucose regulation

Coverage 2013–2025 · Updated 16 Jul 2026

Blood Glucose Must Supply Cells Without Creating Osmotic Stress

State Immediate problem Serious consequence if prolonged
hypoglycaemia too little glucose available, especially to the brain fainting, convulsions or coma
hyperglycaemia plasma water potential falls and water is drawn from tissues dehydration and circulatory damage

Blood glucose rises after carbohydrate absorption. It falls during fasting and prolonged activity as cells remove glucose for respiration.

Glycogen stores buffer these changes. Liver glycogen can support blood glucose; muscle glycogen is primarily a local fuel reserve for muscle activity.

When Glucose Rises, Beta Cells Use Insulin to Promote Removal and Storage

  1. A rise in blood glucose is detected directly by pancreatic beta cells in the islets of Langerhans.
  2. Beta cells secrete insulin into the blood.
  3. Insulin increases glucose uptake by target cells and promotes respiration.
  4. Liver and skeletal muscle convert glucose to glycogen; other excess can be converted to fat.
  5. As blood glucose falls toward the range, insulin secretion decreases.

Insulin is a hormone signal. It does not itself convert glucose into glycogen; it changes target-cell activity so enzymes carry out the conversions.

Two feedback pathways show pancreatic beta cells releasing insulin after blood glucose rises and alpha cells releasing glucagon after blood glucose falls.

When Glucose Falls, Alpha Cells Use Glucagon to Mobilize Liver Stores

  1. A fall in blood glucose is detected directly by pancreatic alpha cells.
  2. Alpha cells secrete glucagon into the blood.
  3. In the liver, glucagon promotes glycogen breakdown and glucose production from non-carbohydrate substrates.
  4. Glucose is released to the blood.
  5. As blood glucose rises toward the range, glucagon secretion decreases.
Feature Insulin branch Glucagon branch
source beta cells alpha cells
trigger high blood glucose low blood glucose
main effect uptake and storage liver glucose release
net result lowers blood glucose raises blood glucose

Glucagon is a hormone; glycogen is a glucose-storage polymer. Glucagon activates cellular pathways—it is not the enzyme that digests glycogen.

A Glucose Tolerance Curve Tests How Quickly the Control System Recovers

  1. Measure fasting blood glucose.
  2. Give a standard oral glucose dose.
  3. Measure blood glucose at defined times after ingestion.
  4. Compare peak height and recovery toward the fasting range.
Curve feature Effective regulation Impaired regulation
starting value within expected fasting range may already be elevated
post-dose peak rises then turns downward often higher or prolonged
later value approaches the starting range remains elevated longer

The curve shows glucose handling under a standardized challenge. Diagnosis uses clinical thresholds and context; one graph alone does not identify the exact cellular cause.

Homeostasis Uses the Same Logic with Different Sensors and Effectors

regulated variable leaves its acceptable range → receptor detects the direction of deviation → coordinator selects an opposing response → effectors alter transfer, storage or metabolism → deviation shrinks → corrective signal declines

System Sensor / coordinator High-side response Low-side response
blood glucose pancreatic islet cells beta cells, insulin, uptake and storage alpha cells, glucagon, liver glucose release
core temperature thermoreceptors and hypothalamus vasodilation and sweating vasoconstriction, shivering and metabolic heat

For any homeostatic explanation, name the variable, direction of deviation, detector, signal, effector action and why that action reverses the deviation.

Blood glucose regulation

[ 8 ]

Explain the control of blood glucose concentrations in humans.

Concept essentials

  • Beta cells secrete insulin when blood glucose is high.
  • Alpha cells secrete glucagon when blood glucose is low.
  • Insulin promotes glucose uptake and glycogen formation, while glucagon promotes glucose release.