Insulin

Question 1

What is insulin and where is it produced?

Answer 1

Insulin is a peptide hormone produced by the beta cells of the pancreatic islets of Langerhans that regulates carbohydrate, fat, and protein metabolism.

Question 2

What is the primary metabolic role of insulin?

Answer 2

Insulin lowers blood glucose by promoting glucose uptake into liver, skeletal muscle, and adipose tissue.

Question 3

How is glucose stored under the influence of insulin?

Answer 3

Glucose is stored as glycogen in the liver and skeletal muscle and as triglycerides in adipocytes.

Question 4

What is the molecular structure of human insulin?

Answer 4

Human insulin consists of 51 amino acids arranged in an A-chain and a B-chain linked by disulfide bonds.

Question 5

How is insulin synthesised in pancreatic beta cells?

Answer 5

Insulin is synthesised as pro-insulin in the rough endoplasmic reticulum and then cleaved into insulin and C-peptide.

Question 6

What triggers insulin release from beta cells?

Answer 6

An increase in intracellular calcium (Ca²⁺) triggers insulin release from secretory granules.

Question 7

Why is C-peptide clinically useful?

Answer 7

C-peptide reflects endogenous insulin production and helps differentiate endogenous insulin secretion from exogenous insulin administration.

Question 8

What stimulates insulin secretion physiologically?

Answer 8

Hyperglycaemia stimulates insulin secretion.

Question 9

How does insulin affect carbohydrate metabolism?

Answer 9

It increases glucose utilisation and promotes glycogen synthesis.

Question 10

How does insulin affect fat metabolism?

Answer 10

It inhibits lipolysis and promotes triglyceride storage.

Question 11

How does insulin affect protein metabolism?

Answer 11

It reduces muscle protein breakdown.

Question 12

What effect does insulin have on potassium balance?

Answer 12

Insulin increases cellular potassium uptake by stimulating the Na⁺/K⁺-ATPase pump.

Question 13

What is an insulinoma?

Answer 13

An insulinoma is a neuroendocrine tumour arising from pancreatic islet cells that secretes insulin inappropriately.

Question 14

What is the epidemiology of insulinoma?

Answer 14

It is the most common pancreatic endocrine tumour; 10% are malignant and 10% are multiple.

Question 15

Which genetic syndrome is associated with multiple insulinomas?

Answer 15

Multiple Endocrine Neoplasia type 1 (MEN-1), present in around 50% of patients with multiple tumours.

Question 16

How do insulinomas typically present clinically?

Answer 16

With recurrent hypoglycaemia, often in the early morning or before meals, causing symptoms such as diplopia and weakness.

Question 17

What additional clinical feature may be seen in insulinoma?

Answer 17

Rapid weight gain due to frequent carbohydrate intake to relieve hypoglycaemia.

Question 18

What biochemical findings support a diagnosis of insulinoma?

Answer 18

High insulin levels, raised proinsulin-to-insulin ratio, and elevated C-peptide.

Question 19

What is the gold-standard diagnostic test for insulinoma?

Answer 19

A supervised prolonged fast of up to 72 hours.

Question 20

Which imaging modality is commonly used to localise an insulinoma?

Answer 20

CT scan of the pancreas.

Question 21

What is the definitive management of insulinoma?

Answer 21

Surgical resection.

Question 22

What medical treatments can be used if surgery is not possible?

Answer 22

Diazoxide and somatostatin analogues.

Question 23

What is the insulin stress test used for?

Answer 23

It is used to assess anterior pituitary function in suspected hypopituitarism.

Question 24

How does the insulin stress test work?

Answer 24

IV insulin induces hypoglycaemia, which should stimulate growth hormone and cortisol release if pituitary function is normal.

Question 25

What is the expected hormonal response in a normal insulin stress test?

Answer 25

Both growth hormone and cortisol levels should rise.

Question 26

What are the contraindications to the insulin stress test?

Answer 26

Epilepsy, ischaemic heart disease, and adrenal insufficiency.

Question 27

What is the most important acute complication of insulin therapy?

Answer 27

Hypoglycaemia.

Question 28

What symptoms should patients be taught to recognise for hypoglycaemia?

Answer 28

Sweating, anxiety, blurred vision, confusion, and aggression.

Question 29

How should hypoglycaemia be treated in a conscious patient?

Answer 29

Give 10–20 g of a short-acting carbohydrate such as glucose tablets, glucose gel, or a sugary drink.

Question 30

What emergency treatment should all insulin-treated patients have access to?

Answer 30

A glucagon kit for use if the patient cannot take oral carbohydrates.

Question 31

What phenomenon may occur in patients with frequent hypoglycaemia?

Answer 31

Reduced hypoglycaemia awareness.

Question 32

How can hypoglycaemia awareness sometimes be restored?

Answer 32

By temporarily relaxing glycaemic control.

Question 33

Which drugs can reduce awareness of hypoglycaemia?

Answer 33

Beta-blockers.

Question 34

What is insulin-related lipodystrophy?

Answer 34

Localised atrophy or lumpiness of subcutaneous fat at injection sites.

Question 35

How can insulin-related lipodystrophy be prevented?

Answer 35

By rotating insulin injection sites.

Question 36

Why is lipodystrophy clinically important?

Answer 36

It can cause erratic and unpredictable insulin absorption.

Question 37

Why is insulin essential in type 1 diabetes mellitus?

Answer 37

It is the only effective treatment due to absolute insulin deficiency.

Question 38

When is insulin commonly used in type 2 diabetes mellitus?

Answer 38

When oral hypoglycaemic agents fail to achieve adequate glycaemic control.

Question 39

How can insulin be classified by manufacturing process?

Answer 39

Porcine insulin, human sequence insulin (enzyme-modified or recombinant), and insulin analogues.

Question 40

What are the key features of rapid-acting insulin analogues?

Answer 40

Onset ~5 minutes, peak ~1 hour, duration 3–5 hours.

Question 41

Which insulins are examples of rapid-acting analogues?

Answer 41

Insulin aspart (NovoRapid) and insulin lispro (Humalog).

Question 42

What are the key features of short-acting insulins?

Answer 42

Onset ~30 minutes, peak ~3 hours, duration 6–8 hours.

Question 43

What are examples of short-acting insulins?

Answer 43

Actrapid and Humulin S.

Question 44

What are intermediate-acting insulins commonly based on?

Answer 44

Isophane insulin.

Question 45

What are the key features of long-acting insulin analogues?

Answer 45

Onset 1–2 hours with a flat profile lasting up to 24 hours.

Question 46

Which long-acting insulins are commonly used?

Answer 46

Insulin detemir (Levemir) and insulin glargine (Lantus).

Question 47

What is the purpose of premixed insulin preparations?

Answer 47

To combine basal and bolus insulin in a single injection.

Question 48

What is Novomix 30 composed of?

Answer 48

30% insulin aspart (rapid-acting) and 70% insulin aspart protamine (intermediate-acting).

Question 49

What is Humalog Mix25 composed of?

Answer 49

25% insulin lispro and 75% insulin lispro protamine.

Question 50

What is Humulin M3 composed of?

Answer 50

30% soluble insulin and 70% isophane insulin.

Question 51

What is the most common route of insulin administration?

Answer 51

Subcutaneous injection.

Question 52

Why must injection sites be rotated?

Answer 52

To prevent lipodystrophy.

Question 53

How do insulin pumps deliver insulin?

Answer 53

They provide continuous basal insulin with patient-activated bolus doses at meal times.

Question 54

When is intravenous insulin used?

Answer 54

In acutely unwell patients, such as those with diabetic ketoacidosis.