4.8.2Additional lessons
Regulation of Blood Glucose — IB Biology SL Revision Notes & Topical Questions
5 min read 5 parts Lesson 130 of 142
Part 1 of 5The Pancreas
Islets of Langerhans
- Groups of endocrine cells in the pancreas that monitor blood glucose and secrete hormones.
Beta cells
- They secrete insulin when blood glucose concentration rises above the set point.
Alpha cells
- They secrete glucagon when blood glucose concentration falls below the set point.
Other tissue
- Most pancreatic tissue makes digestive enzymes and is separate from the islets.
Part 2 of 5Lowering Glucose: Insulin
1
After a meal, glucose absorbed from the gut raises the blood glucose concentration.
2
Beta cells detect the rise and secrete insulin into the blood.
3
Insulin binds to receptors on target cells, mainly in the liver and muscle, and increases glucose uptake by facilitated diffusion.
4
The liver and muscles convert glucose into glycogen for storage, a process called glycogenesis.
5
Respiration of glucose rises, so blood glucose falls back to the set point and insulin secretion falls.
Part 3 of 5Raising Glucose: Glucagon
Raising Glucose: Glucagon
Trigger
- Between meals or during exercise, a fall in blood glucose stimulates alpha cells to release glucagon.
Target
- Glucagon travels in the blood and acts on liver cells.
Glycogenolysis
- The liver breaks down stored glycogen into glucose, which is released into the blood.
Result
- Blood glucose rises to the set point and glucagon release is switched off.
Antagonistic action
- Insulin and glucagon have opposite effects, so the two together give precise control.
Part 4 of 5Diabetes Mellitus
Type 1
- The immune system destroys beta cells, so little or no insulin is made;
- treatment is regular insulin injections and monitoring glucose.
Type 2
- Target cells become less responsive to insulin, and treatment involves diet, exercise and sometimes medication.
Symptoms
- High blood glucose may cause thirst, fatigue, frequent urination and glucose in the urine.
Long-term risks
- Poorly controlled blood glucose can damage blood vessels, nerves, kidneys and eyes.
| Feature | Type 1 | Type 2 |
|---|---|---|
| Cause | Beta cells destroyed | Reduced response to insulin |
| Insulin | Little or none | Often present |
| Main control | Insulin injections | Diet, exercise, medication |
Part 5 of 5Exam Checklist & Tips
4.8.2 – Key Points for the Exam
- Insulin Hormone from beta cells that lowers blood glucose.
- Glucagon Hormone from alpha cells that raises blood glucose.
- Glycogen Branched polysaccharide used to store glucose in animal cells.
- Glycogenesis Conversion of glucose to glycogen.
- Diabetes mellitus A condition where blood glucose is not properly controlled.
Common Mistakes
- Confusing glucagon, the hormone, with glycogen, the storage carbohydrate.
- Stating that insulin converts glycogen to glucose.
- Saying beta cells secrete glucagon.
- Saying type 2 diabetics make no insulin; the cells respond poorly.
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