Blood glucose regulation (AQA GCSE Biology Combined Science): Revision Notes
Blood glucose regulation
What controls blood glucose?
Your pancreas is the key organ that watches and controls how much glucose is in your blood. It acts like a monitoring system that keeps glucose levels steady.
The pancreas does this by making a hormone called insulin when it detects that blood glucose is getting too high.
The pancreas is essentially your body's glucose control centre, constantly monitoring blood sugar levels and responding immediately when they start to rise or fall outside the normal range.
How insulin works
Insulin is a chemical messenger (hormone) that your pancreas releases into your bloodstream. When insulin reaches your body's cells, it causes several important things to happen:
- Cells absorb more glucose from the blood, which makes blood glucose levels drop
- Muscle cells and liver cells convert the absorbed glucose into glycogen for storage
- This removes excess glucose from the blood and stores it safely for later use
Think of insulin as a key that opens the doors of your cells to let glucose in.
Storing glucose for later
Your body is clever - it doesn't waste extra glucose. Instead, it stores it in two main forms:
Glycogen is how animals (including humans) store glucose:
- Made when many glucose molecules join together
- Stored mainly in liver cells and muscle cells
- Can be quickly broken down when you need energy
Starch is how plants store glucose:
- Also made from many glucose molecules joined together
- Stored in plant cells
- This is why foods like potatoes and bread give us energy
Both glycogen and starch are essentially glucose storage molecules, but they're structured slightly differently. Your body can only store a limited amount of glycogen, which is why excess glucose gets converted to fat for long-term storage.
The control mechanism
Blood glucose control works like a thermostat in your home. Here's how the system maintains steady glucose levels:
This control system uses negative feedback because the response reverses the original change. This is crucial for maintaining homeostasis - your body's ability to keep internal conditions stable.
When blood glucose rises (like after eating):
Step 1: Pancreas detects the rise in glucose concentration Step 2: Pancreas increases insulin secretion Step 3: Insulin causes muscle and liver cells to remove glucose from blood Step 4: Glucose gets stored as glycogen Step 5: Blood glucose concentration falls back to normal
When blood glucose falls (like after exercise):
Step 1: Pancreas detects the fall in glucose concentration Step 2: Pancreas decreases insulin secretion Step 3: Less glucose is absorbed by cells Step 4: Blood glucose concentration rises back to normal
What happens after you eat
When you eat a meal containing starch and sugar, your blood glucose follows a predictable pattern:
Timeline of Blood Glucose After Eating:
First hour: Your blood glucose rises as starch gets digested into glucose and absorbed
After 1-2 hours: Insulin levels increase, so liver and muscle cells start absorbing lots of glucose
2-4 hours later: Blood glucose falls back to normal levels as glucose gets converted to glycogen for storage
The graph shows this as a rise and then fall in blood glucose concentration over time.
Remember!
Key Points to Remember:
- Your pancreas monitors and controls blood glucose levels
- Insulin is the hormone that lowers blood glucose by making cells absorb it
- Excess glucose gets stored as glycogen in liver and muscle cells
- The control system uses negative feedback to keep glucose levels steady
- After eating, blood glucose rises then falls as insulin does its job