AQA A Level Biology

Revision Notes

6.4.7 Diabetes

The Causes of Diabetes

  • There are over 3 million people suffering from diabetes in the UK
  • Diabetes is a condition in which the homeostatic control of blood glucose has failed or deteriorated
  • In individuals with diabetes their insulin function is disrupted which allows the glucose concentration in the blood to rise
    • The kidneys are unable to filter out this excess glucose in the blood and so it often appears in the urine
    • The increased glucose concentration also causes the kidneys to produce large quantities of urine, making the individual feel thirsty due to dehydration
  • There are two different types of diabetes: type I and type II

Type I diabetes

  • Type 1 diabetes is a condition in which the pancreas fails to produce sufficient insulin to control blood glucose levels
  • It normally begins in childhood due to an autoimmune response whereby the body’s immune system (T cells) attacks the β cells of the islets of Langerhans in the pancreas
    • The β cells detect high blood sugar and synthesise insulin
  • The lack of insulin also affects glycogen stores which results in an individual feeling fatigued
  • If the blood glucose concentration reaches a dangerously high level after a meal then organ damage can occur
  • Type 1 diabetes is normally treated with regular blood tests, insulin injections and a diabetes appropriate diet
    • Health authorities encourage diabetics to eat a similar diet to the general public. They suggest five portions of fruit and veg a day, minimally processed food and consuming more polysaccharides than monosaccharides or disaccharides
  • The insulin used by diabetics can be fast-acting or slow-acting; each allowing for a different level of control
  • If a type I diabetic manages their condition well they can live a very full life

Type II diabetes

  • Type II diabetes is more common than type I
  • It usually develops in those aged 40 and over however more and more young people are developing the condition
  • In type II diabetes the pancreas still produces insulin but the receptors have reduced in number or no longer respond to it
    • This reduced sensitivity to insulin occurs in the liver and fat storage tissues
  • The lack of response to insulin means there is a reduced glucose uptake which leads to an uncontrolled high blood glucose concentration
    • This can cause the β cells to produce larger amounts of insulin which ultimately damages them
  • For early-stage type II diabetes, a sugar and fat controlled diet and an exercise regime are usually sufficient treatments
    • Any food that is rapidly digested into sugar will cause a sudden, dangerous spike in blood sugar
  • Obesity is a major risk factor for type II diabetes; a person who is obese likely consumes a diet high in carbohydrates, and the over-production of insulin triggers the development of insulin resistance

Type I diabetes and type II diabetesComparing Type 1 & Type 2 diabete_1, downloadable IGCSE & GCSE Biology revision notes

Diabetes and blood pressure

  • Individuals with poorly controlled diabetes often suffer from high blood pressure
  • The high blood glucose concentration lowers the water potential of the blood which causes more water to move from the tissues into the blood vessels by osmosis
  • As a result, there is a larger volume of blood within the circulatory system which causes blood pressure to increase

Exam Tip

A common exam question:

Explain why the protein insulin must be administered intravenously rather than orally.

Insulin is a protein, if it was taken orally it would be digested by the enzyme protease found in the gut before entering the bloodstream.

Evaluating Data on Type 2 Diabetes

  • Correlation is an association or relationship between variables
  • Causation occurs when one variable has an influence or is influenced by another
  • There is a clear distinction between correlation and causation: a correlation does not necessarily imply a causative relationship

Recognising Correlations and Causal Relationships

  • Scientists present their findings from experiments in graphical and numerical forms to identify if there are relationships between risk factors and certain disease
  • Scatter diagrams are used to identify correlations between two variables to determine if a factor (such as obesity) does increase the risk of developing a disease (such as type 2 diabetes)
    • In this example, BMI would be on the x-axis and Incidence of Type 2 Diabetes on the y-axis
    • It is important to note that not everyone with a high BMI will develop type II diabetes, however more people with a high BMI will develop type II diabetes than those with low BMI
  • Correlation can be positive or negative
    • Positive correlation: as variable A increases, variable B increases
    • Negative correlation: as variable A increases, variable B decreases
  • If there is no correlation between variables the correlation coefficient will be 0

Types of correlation graphs, downloadable AS & A Level Biology revision notes

Image showing different types of correlation in scatter graphs

Risk factors & causal relationships for type II diabetes

  • A correlation exists between obesity and the risk of developing type II diabetes
    • Those with a BMI (body mass index) that indicates obesity are more likely to have an unbalanced diet with excess sugary and fatty foods. The large amounts of sugar lead to increased insulin production and the development of insulin resistance
    • Obesity is also linked with inactivity, exercise aids the body’s sugar metabolism
  • The percentage of the population that are obese in the UK is rising
    • This is thought to be due to the western diet – a diet that is composed of energy-rich ‘fast foods’ and a sedentary lifestyle
  • When analysing data and studies it is always important to remember that risk factors interact with each other
    • For example, an obese individual that is inactive is more likely to develop type II diabetes than an inactive individual who is not obese
  • Even though there is a correlation, this does not mean that there is a direct causal link
    • There is a correlation between obesity and the incidence of type II diabetes however scientists still do not fully understand the mechanism behind this due to interacting factors

Author: Lára

Lára graduated from Oxford University in Biological Sciences and has now been a science tutor working in the UK for several years. Lára has a particular interest in the area of infectious disease and epidemiology, and enjoys creating original educational materials that develop confidence and facilitate learning.
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