Diabetes (AQA A-Level Biology): Revision Notes

Diabetes

Diabetes mellitus is a metabolic disorder where individuals cannot properly control their blood glucose levels. This happens either because the body cannot produce enough insulin or because cells do not respond effectively to insulin. The condition affects approximately 350 million people globally, with 3.2 million cases in the UK alone. An additional 1 million people in the UK may have undiagnosed diabetes.

Types of diabetes

There are two main forms of diabetes, each with distinct causes and characteristics.

Type 1 diabetes

Type 1 diabetes occurs when the body cannot produce insulin at all. This form typically develops during childhood and progresses rapidly over just a few weeks. The underlying cause involves an autoimmune response where the body's immune system mistakenly attacks and destroys the beta cells located in the islets of Langerhans within the pancreas. These beta cells are responsible for insulin production.

The autoimmune destruction means that people with Type 1 diabetes produce no insulin naturally. Without insulin, glucose cannot enter cells effectively, leading to dangerously high blood glucose levels. The rapid onset means symptoms become obvious quickly, making diagnosis relatively straightforward.

Type 2 diabetes

Type 2 diabetes develops when cells lose their ability to respond to insulin effectively, even though the pancreas may still produce some insulin. This condition typically affects people over 40 years old and develops gradually over months or years. The slow progression means symptoms may be mild initially and can go unnoticed.

Several factors contribute to Type 2 diabetes development. Glucose receptors on cell membranes may become less sensitive to insulin or decrease in number. Additionally, the pancreas may not produce adequate amounts of insulin to meet the body's needs. Rising obesity rates and poor dietary habits have led to increasing numbers of adolescents developing Type 2 diabetes. Approximately 90% of all diabetes cases are Type 2.

Signs and symptoms of diabetes

The body shows various signs when blood glucose levels remain consistently elevated. High blood glucose concentration is the primary indicator, often accompanied by glucose appearing in urine as the kidneys attempt to remove excess sugar from the blood.

People with diabetes frequently experience the following key symptoms:

• Excessive urination as the body tries to eliminate surplus glucose
• Increased thirst and hunger as the body becomes dehydrated and cells cannot access glucose for energy
• Weight loss despite increased appetite, as cells cannot utilise glucose effectively and begin breaking down fat and muscle for energy
• Genital itching and regular episodes of thrush due to high glucose levels encouraging bacterial growth
• Tiredness from cells lacking energy
• Blurred vision caused by glucose affecting fluid levels in the eyes

Control and management of diabetes

While diabetes cannot be cured completely, recent advances in insulin-producing cell transplantation show promise. Current management strategies differ significantly between the two types.

Managing type 1 diabetes

Type 1 diabetes requires insulin injections because the body produces none naturally. Insulin cannot be taken orally because digestive enzymes would break down this protein hormone before it could be absorbed. Instead, insulin must be injected directly into the bloodstream, typically two to four times daily.

The insulin dose must match glucose intake carefully. Taking too much insulin causes hypoglycaemia (dangerously low blood glucose), which can result in unconsciousness. To prevent this, people with Type 1 diabetes monitor their blood glucose using biosensors - devices that measure glucose levels in blood samples.

Successful management involves balancing insulin injections with carbohydrate intake and physical exercise. Regular monitoring allows individuals to adjust insulin doses based on their glucose readings, maintaining blood glucose within safe ranges.

Managing type 2 diabetes

Type 2 diabetes management typically begins with dietary modifications and increased physical exercise. Reducing carbohydrate intake helps limit glucose absorption from food, while exercise increases glucose uptake by muscles, naturally lowering blood glucose levels.

When lifestyle changes prove insufficient, additional treatments may include insulin injections or medications that stimulate insulin production by the pancreas. Some drugs work by slowing glucose absorption from the intestine, helping prevent blood glucose spikes after meals.

Blood glucose response patterns

The way blood glucose levels change after consuming glucose differs markedly between people with diabetes and those without the condition.

In individuals without diabetes, blood glucose rises moderately after consuming glucose, then returns to normal levels within 2-3 hours. This happens because beta cells release insulin in response to rising glucose levels, enabling cells to absorb glucose efficiently.

People with Type 1 diabetes show a dramatically different pattern. Their blood glucose levels rise much higher after consuming glucose and remain elevated for extended periods. Without insulin production, glucose cannot enter cells effectively, so blood glucose concentration decreases very slowly as cells gradually use the available glucose.

The comparison reveals why insulin therapy is essential for Type 1 diabetes management and demonstrates how the body's natural glucose regulation system fails when insulin production stops.