SN5
SHORT NOTE
5M
★ High-yield
Define diabetes mellitus. Give its diagnostic criteria, types and complications.
Definition
Diabetes mellitus = a group of metabolic disorders characterised by chronic hyperglycaemia resulting from defects in insulin secretion, insulin action, or both.
Diagnostic Criteria (WHO / Ada)
| Test | Diabetes | Prediabetes |
|---|---|---|
| Fasting plasma glucose | ≥ 126 mg/dL | 100–125 (impaired fasting glucose) |
| 2-h post 75 g glucose | ≥ 200 mg/dL | 140–199 (impaired glucose tolerance) |
| HbA1c | ≥ 6.5% | 5.7–6.4% |
| Random glucose + symptoms | ≥ 200 mg/dL | — |
Types
| Feature | Type 1 | Type 2 |
|---|---|---|
| Defect | Absolute insulin deficiency | Insulin resistance + relative deficiency |
| Cause | Autoimmune β cell destruction | Obesity, genetic, lifestyle |
| Age at onset | Usually < 30 years | Usually > 40 years |
| Body habitus | Lean | Obese |
| Ketosis | Prone | Uncommon |
| C-peptide | Absent or low | Normal or high |
| Treatment | Insulin essential | Diet, exercise, oral agents, sometimes insulin |
| Share of cases | 5–10% | 90–95% |
Pathophysiology of Symptoms
Insulin deficiency or resistance → ↓ Glucose uptake + ↑ hepatic output → Hyperglycaemia → Exceeds renal threshold (180 mg/dL) → Glycosuria → osmotic diuresis → polyuria → dehydration → polydipsia; cellular starvation → polyphagia with weight loss
Complications
| Type | Complications |
|---|---|
| Acute | Diabetic ketoacidosis (type 1); hyperosmolar hyperglycaemic state (type 2); hypoglycaemia from treatment |
| Microvascular | Retinopathy (leading cause of blindness), nephropathy (leading cause of end-stage renal disease), neuropathy |
| Macrovascular | Coronary artery disease, stroke, peripheral vascular disease |
| Other | Diabetic foot, infections, cataract, delayed wound healing |
- Mechanisms — non-enzymatic glycation (advanced glycation end products), the polyol pathway (sorbitol accumulation), and oxidative stress
Applied Aspects
- HbA1c reflects the average glucose over 8–12 weeks — the standard measure of control; target below 7%
- India has one of the largest diabetic populations in the world, with onset a decade earlier and at a lower BMI than in Western populations
- Tight glycaemic control prevents microvascular complications; macrovascular risk needs blood pressure and lipid control as well
All questions in Endocrine System
- Q1Describe the synthesis, transport and actions of thyroid hormones. Explain the regulation of thyroid secretion. ★
- Q2Describe the source, synthesis, actions and regulation of insulin. Add a note on glucagon. ★
- Q3Enumerate the hormones of the adrenal cortex. Describe the actions and regulation of cortisol and aldosterone. ★
- Q4Describe the actions and regulation of growth hormone. Add a note on the disorders of its secretion. ★
- Q5Describe the regulation of plasma calcium. Explain the actions of parathyroid hormone, vitamin D and calcitonin. ★
- SN1Write a short note on hypothyroidism. Describe cretinism and myxoedema. ★
- SN2Write a short note on Cushing syndrome. ★
- SN3Describe the hormones of the adrenal medulla and their actions. Differentiate adrenaline from noradrenaline. ★
- SN4Write a short note on oxytocin. ★
- SN5Define diabetes mellitus. Give its diagnostic criteria, types and complications. ★
- SN6Write a short note on Addison disease. ★
- SN7Enumerate the thyroid function tests and describe their interpretation.