Blood Glucose Regulation and Diabetes
Blood Glucose Control
The concentration of glucose in the blood must be kept within a narrow range. If it is too high or too low, cells cannot function properly and it can be life-threatening.
Blood glucose levels are controlled by the pancreas, which monitors blood glucose and responds by releasing one of two hormones: insulin or glucagon.
When Blood Glucose Is Too HIGH
1. The pancreas detects high blood glucose (e.g. after eating a carbohydrate-rich meal)
2. Beta cells in the pancreas release insulin into the blood
3. Insulin causes:
- Body cells (especially liver and muscle cells) to take up glucose from the blood
- Glucose to be converted to glycogen for storage in the liver and muscles
- Cells to use more glucose in respiration
4. Blood glucose level falls back to normal
When Blood Glucose Is Too LOW
1. The pancreas detects low blood glucose (e.g. after exercise or between meals)
2. Alpha cells in the pancreas release glucagon into the blood
3. Glucagon causes:
- The liver to convert stored glycogen back into glucose
- This glucose is released into the blood
4. Blood glucose level rises back to normal
Negative Feedback
This system is an example of negative feedback:
- A change from the normal level is detected
- A response is triggered to reverse the change
- The system returns to normal
- Once normal, the response stops
Insulin and glucagon have opposing (antagonistic) effects — they work together to keep blood glucose stable.
Type 1 Diabetes
Type 1 diabetes is a condition where the pancreas produces little or no insulin. It is an autoimmune disease — the immune system destroys the beta cells.
| Feature | Detail |
|---|---|
| Cause | Autoimmune destruction of beta cells; thought to have a genetic component |
| Age of onset | Usually develops in childhood or adolescence |
| Treatment | Insulin injections (or insulin pump) — insulin must be injected because it is a protein and would be digested if swallowed |
| Management | Monitor blood glucose regularly; match insulin dose to food intake and activity; careful diet planning |
| Is it curable? | Currently no cure — lifelong condition |
Type 2 Diabetes
Type 2 diabetes is a condition where the body's cells become resistant to insulin (they no longer respond to it properly) or the pancreas does not produce enough insulin.
| Feature | Detail |
|---|---|
| Cause | Strongly linked to obesity, poor diet, lack of exercise, age, and genetics |
| Age of onset | Usually develops in adults over 40, but increasingly seen in younger people due to rising obesity |
| Treatment | Diet and exercise — eating a balanced diet with controlled carbohydrate intake; regular physical activity |
| Medication | If lifestyle changes are insufficient, drugs such as metformin may be prescribed (helps cells respond to insulin) |
| Is it curable? | Can sometimes be reversed with significant weight loss and lifestyle changes |
Comparing Type 1 and Type 2 Diabetes
| Feature | Type 1 | Type 2 |
|---|---|---|
| Insulin production | Little or none | Some produced but cells are resistant |
| Cause | Autoimmune (genetic) | Lifestyle (mainly obesity) |
| Onset | Childhood/adolescence | Usually adulthood |
| Treatment | Insulin injections | Diet, exercise, medication |
| Prevalence | ~10% of diabetes cases | ~90% of diabetes cases |
| Prevention | Cannot be prevented | Can often be prevented by healthy lifestyle |
The Kidneys and Water Balance
The kidneys regulate water and ion balance and remove waste products:
- Urea (from deamination of amino acids in the liver) is filtered out and excreted in urine
- Excess water and ions are removed
- Useful substances like glucose, amino acids, and some water are reabsorbed back into the blood
ADH and Water Balance
ADH (antidiuretic hormone) controls how much water the kidneys reabsorb:
- If blood is too concentrated (dehydrated): the pituitary gland releases more ADH → kidneys reabsorb more water → small volume of concentrated urine
- If blood is too dilute (overhydrated): the pituitary gland releases less ADH → kidneys reabsorb less water → large volume of dilute urine
This is another example of negative feedback.
Thermoregulation
The body maintains a core temperature of about 37°C because this is the optimum for enzyme activity.
If body temperature is too HIGH:
- Blood vessels near the skin surface vasodilate (widen) → more blood flows near the surface → more heat is radiated away
- Sweat glands produce more sweat → sweat evaporates from the skin surface, transferring heat energy to the environment
- Body hairs lie flat (less insulation)
If body temperature is too LOW:
- Blood vessels vasoconstrict (narrow) → less blood flows near the surface → less heat lost
- Shivering — muscles contract rapidly, generating heat from increased respiration
- Body hairs stand erect (in animals, traps a layer of insulating air; less effective in humans)
- Less sweat is produced
The thermoregulatory centre in the hypothalamus (part of the brain) monitors blood temperature and has receptors in the skin that detect external temperature.
Exam Tips
- Know the difference between insulin (lowers glucose) and glucagon (raises glucose) — they are NOT the same
- Type 1 = no insulin produced; Type 2 = insulin resistance — do not mix these up
- ADH is produced by the pituitary gland and acts on the kidneys
- Vasodilation is NOT "blood vessels moving closer to the surface" — it is the vessels widening