Which statement best defines diabetes mellitus?

• A. Insulin is secreted in excess
• B. Blood glucose levels remain normal
• C. Insulin is not secreted adequately or tissues are resistant to its effects
• D. Pancreas fails to regulate glucagon

Answer: (C)

Diabetes mellitus is a condition where glucose cannot enter body cells effectively because insulin action is inadequate or the body's tissues don’t respond to insulin. This happens when there isn’t enough insulin secreted or the tissues are resistant to its effects, leading to elevated blood glucose. With insufficient insulin or insulin resistance, glucose stays in the bloodstream rather than entering muscle and fat cells, causing hyperglycemia and related complications. That’s why the statement describing inadequate insulin secretion or insulin resistance is the best definition. The other options don’t fit: producing insulin in excess wouldn’t cause diabetes, normal blood glucose isn’t characteristic of diabetes, and while glucagon regulation can be affected, it doesn’t define the condition as accurately as insulin deficiency or resistance does.