Homeostasis: Question 7

Worked solution

Part (a): What is diabetes mellitus, and the cause of type 1

Diabetes mellitus is a condition in which blood glucose concentration is not properly controlled by the body’s normal homeostatic mechanisms, so that it remains persistently too high, a state called hyperglycaemia.

Type 1 diabetes mellitus results from an autoimmune response: the person’s own immune system attacks and destroys the β (beta) cells of the islets of Langerhans in the pancreas. Because these are the cells that produce and secrete insulin, little or no insulin can be released, even when blood glucose concentration rises after a meal. Type 1 diabetes usually develops in childhood or early adulthood and is not caused by diet or body mass.

Part (b): The cause of type 2, and a risk factor

Type 2 diabetes mellitus does not usually involve destruction of the β cells. Instead, the target cells of insulin (mainly liver, muscle and fat cells) become progressively less responsive to insulin, because the sensitivity of their insulin receptors is reduced. This is called insulin resistance. Even though the pancreas may still be secreting insulin (often at a higher-than-normal concentration in the earlier stages, as the body tries to compensate), blood glucose concentration is not lowered effectively, so it remains too high.

A recognised risk factor for type 2 diabetes is being overweight or obese (other accepted risk factors include physical inactivity, increasing age, and a family history/genetic predisposition).

Part (c): Why treatment differs between the two types

Because type 1 diabetes results from an almost complete inability to produce insulin, it is normally treated with regular insulin injections (or an insulin pump), replacing the hormone the body can no longer make.

Because type 2 diabetes usually still involves some insulin production, the problem being reduced sensitivity of target cells, it is often managed first through changes to diet and exercise (including weight loss), and sometimes with oral drugs that improve insulin secretion or the sensitivity of target cells to insulin, rather than starting immediately with insulin injections. This difference in treatment reflects the different underlying cause: type 1 is a problem of insulin supply, while type 2 is primarily a problem of insulin effectiveness at the target cells.

Final answers

• (a) Diabetes mellitus is the failure to control blood glucose concentration, leading to persistent hyperglycaemia; type 1 is caused by autoimmune destruction of the β cells, so little or no insulin is produced.
• (b) Type 2 is caused by reduced sensitivity of target cells (insulin resistance) so that insulin has a smaller effect even when present; a risk factor is being overweight/obese.
• (c) Type 1 is usually treated with insulin injections (insulin cannot be produced); type 2 is often treated first through diet, exercise and/or drugs that improve insulin sensitivity or secretion, since some insulin is usually still produced.