Homeostasis
Structures and Functions in Living Organisms · 4 question types
Exam Frequency Analysis
Past paper frequency (2018 to 2024)
This topic accounts for approximately 16% of your exam marks.
Blood glucose regulation and temperature control are increasing in frequency; insulin/glucagon tested every series.
Diabetes mellitus is a chronic condition in which the body fails to control its blood glucose properly, so glucose levels rise to dangerously high values after a meal and stay high. There are two main forms: Type 1 and Type 2.
Type 1 diabetes
In Type 1 diabetes, the body's own immune system has attacked and destroyed the insulin-producing cells in the pancreas. The pancreas can no longer make insulin, so there is nothing to stop blood glucose climbing after a meal.
- Cause: an autoimmune attack on the pancreas. The reason this happens is not fully understood; genetics and viral infections in childhood are both thought to play a role.
- Usually appears in childhood or young adulthood.
- Not preventable and not linked to lifestyle.
- Treatment: lifelong injections before meals (insulin cannot be taken as a tablet because the stomach would digest it). The dose is adjusted based on what the patient eats and how active they are. Modern patients often use an insulin pump that delivers a continuous dose plus extra at meals, or a continuous glucose monitor that helps fine-tune the doses.
- Patients also have to:
- Monitor blood glucose regularly with a finger-prick test
- Eat a controlled carbohydrate diet with regular meals
- Exercise regularly (but with awareness, since exercise lowers blood glucose)
Type 2 diabetes
In Type 2 diabetes, the pancreas still makes insulin (at least to begin with), but the body cells stop responding to it properly. The cells become insulin-resistant: they no longer take up glucose efficiently in response to the hormone, so blood glucose stays high.
- Cause: strongly linked to lifestyle factors including obesity, lack of physical activity, and a diet high in sugar and processed carbohydrates. There is also a genetic predisposition in some families.
- Usually appears in adulthood, although increasingly in younger people because of rising rates of childhood obesity.
- Mostly preventable with lifestyle changes.
- Treatment:
- Lifestyle changes first: weight loss, more exercise, lower-carbohydrate diet, eating smaller more frequent meals
- Tablets (such as metformin) that help the body's cells respond to insulin better, or that slow down glucose absorption from the gut
- Insulin injections are sometimes needed eventually, if the pancreas wears out over many years
Side-by-side comparison
| Type 1 | Type 2 | |
|---|---|---|
| Cause | Autoimmune destruction of insulin-producing pancreatic cells | Body cells become resistant to insulin; pancreas eventually wears out |
| Insulin production? | No, or very little | Yes (at least at first) |
| Age of onset | Usually childhood / young adult | Usually adult (over 40), but rising in younger people |
| Linked to lifestyle? | No | Yes: obesity, inactivity, poor diet |
| Preventable? | No | Largely yes |
| First-line treatment | Insulin injections | Lifestyle changes, then tablets |
| Approximate share of cases | ≈ 10% of diabetics | ≈ 90% of diabetics |
Symptoms and complications
Symptoms of untreated or poorly-controlled diabetes are similar for both types and reflect the high blood glucose:
- Frequent urination: high blood glucose forces the kidneys to excrete some of the excess in urine. To carry the glucose out, the kidneys also lose extra water, so urine volume rises.
- Constant thirst: the body needs to replace all the water lost in urine.
- Tiredness: glucose cannot enter the cells properly, so cells are short on fuel.
- Sugar in the urine: a positive Benedict's test on a sample of urine is a classic warning sign.
- Slow wound healing and frequent infections.
- Unexplained weight loss (especially in Type 1, where the body starts breaking down fat and muscle for energy).
Long-term complications of uncontrolled diabetes include damage to the eyes (leading to blindness), kidneys (leading to kidney failure), nerves (leading to loss of sensation, especially in the feet), and blood vessels (leading to heart attacks, strokes, and poor circulation in the legs).