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6.4.7Organisms Respond to Changes in their Environments (A Level only)

Diabetes — AQA A Level Biology 7402 Revision Notes & Topical Questions

5 min read 9 parts Lesson 39 of 44 1 quiz

📚 AQA A Level Biology 7402 Hub / Topical Revision
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6.4.7 Diabetes — AQA A Level Biology 7402 notes: Describe the causes, symptoms and treatment of type 1 and type 2 diabetes and interpret glucose tolerance data.Diabetes mellitus is a condition in which the control of blood glucose fails and the concentration remains too high (hyp…

  • glucose tolerance test
  • Exam-style question 1
  • Exam-style question 2
  • Exam-style question 3
  • Type 1 diabetes
  • Glycosuria

Part 1 of 7What is diabetes mellitus?

Diabetes mellitus is a condition in which the control of blood glucose fails and the concentration remains too high (hyperglycaemia).

1
When blood glucose is above the renal threshold, the nephron cannot reabsorb all the glucose, so glucose appears in the urine (glycosuria).
2
The glucose in the filtrate lowers its water potential,
  • so less water is reabsorbed by osmosis and a large volume of urine is produced, causing thirst.
3
Other symptoms include tiredness,
  • because cells cannot take up glucose, weight loss as fat and protein are broken down as an alternative fuel, and blurred vision.
4
There are two main types.

Part 2 of 7Type 1 and type 2

FeatureType 1Type 2
CauseAutoimmune destruction of β cells, so little or no insulin is producedTarget cell receptors become less responsive to insulin (insulin resistance); β cells may later produce too little
Usual onsetChildhood or early adulthoodUsually adults, increasingly younger
Risk factorsGenetic factors, possible viral triggerObesity, lack of exercise, poor diet, age, family history, ethnicity
TreatmentInsulin injections or pump, matched to diet and exerciseDiet control and exercise; drugs that increase insulin release or sensitivity; insulin later if needed

Part 3 of 7Treatment of type 1 diabetes

People with type 1 diabetes must inject insulin, because it is a protein and would be digested if taken by mouth.

1
Doses are matched to food intake and activity, and blood glucose is monitored using a meter or a continuous glucose sensor.
2
Too much insulin or too little food causes hypoglycaemia, with sweating, confusion and unconsciousness, which is treated with sugary food or glucagon.
3
The insulin used today is human insulin made by genetically modified bacteria or yeast that contain the human insulin gene.
4
This has advantages over the pig or cattle insulin used in the past: it is identical to the human hormone so there is less risk of immune rejection, it can be produced in large amounts, it avoids the ethical objections of some groups,
  • and the risk of infection from animal tissues is lower.

Part 4 of 7Management of type 2 diabetes

Type 2 diabetes is often controlled by lifestyle changes: a diet low in refined sugar and saturated fat, with controlled intake of carbohydrate, weight loss and regular exercise.

Management of type 2 diabetes
Drugs such as metformin reduce glucose production in the liver and increase the sensitivity of cells to insulin; others,
  • such as sulfonylureas, stimulate β cells to release more insulin by closing K+ channels.
Long-term high glucose damages small blood vessels and nerves,
  • which leads to kidney failure, retinal damage and poor circulation in the feet,
  • so good control is important.

Part 5 of 7Glucose tolerance tests and data

In a glucose tolerance test, a person fasts and then drinks a glucose solution.

1
Blood glucose is measured at intervals.
2
In a healthy person it rises, then returns to normal within about two hours.
3
In a diabetic it starts higher and rises to a higher peak, and it remains high after two hours.
4
When describing such a graph, quote the starting level, peak and level at two hours.
5
For a type 1 patient, explain the high value by lack of insulin, and for a type 2 patient, by the failure of cells to respond.
6
Cause and effect should be tested with care: the correlation between obesity and type 2 diabetes does not by itself prove that obesity causes it, though evidence from many studies supports a link.

Part 6 of 7Stem cells and future treatments

Possible future treatments for type 1 diabetes include pancreas or islet transplants, and the use of stem cells to produce new β cells. Immunosuppressant drugs are needed after transplants to prevent rejection. These areas involve ethical discussions about the use of stem cells and about the benefit and risk of lifelong drug treatment.

Exam questions often ask for advice to a patient with type 2 diabetes: reduce body mass, take regular exercise, and eat foods that release glucose slowly, because these changes improve the sensitivity of cells to insulin. A good answer links each piece of advice to the mechanism, rather than simply stating it, and mentions that early diagnosis from a glucose tolerance test or urine test lowers the risk of complications.

Part 7 of 7Exam-style questions

  1. Explain why glucose appears in the urine of an untreated diabetic person. [3]3 marks

  2. Compare the causes of type 1 and type 2 diabetes. [3]3 marks

  3. Explain why insulin must be injected and not taken by mouth. [2]2 marks

Key terms

TermMeaning
Diabetes mellitusCondition in which blood glucose control fails
Type 1 diabetesAutoimmune destruction of insulin-secreting β cells
Type 2 diabetesReduced responsiveness of cells to insulin
GlycosuriaPresence of glucose in urine
HypoglycaemiaBlood glucose too low
Glucose tolerance testTest following blood glucose after a glucose drink
Insulin resistanceTarget cells responding poorly to insulin

Avoid these mistakes

1
Saying type 2 diabetes is caused by lack of insulin only; insulin resistance is the main cause.
2
Saying insulin can be taken as a tablet.
3
Confusing diabetes mellitus with diabetes insipidus.
4
Writing that glucose is not filtered in diabetes; it is filtered but not all is reabsorbed.
5
Forgetting that excess insulin can cause hypoglycaemia.

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