A 68-year-old woman falls on her outstretched hand. X-ray shows a fracture of the surgical neck of the humerus. She later cannot abduct her arm beyond the first few degrees and has numbness over the lateral side of the upper arm. Which muscle is most likely paralysed?

A) Supraspinatus
B) Deltoid
C) Infraspinatus
D) Teres major
E) Latissimus dorsi

Correct answer: B) Deltoid

The axillary nerve winds around the surgical neck of the humerus and is injured in these fractures. It supplies the deltoid and teres minor, and its upper lateral cutaneous branch supplies the skin over the lower deltoid. Supraspinatus can still start abduction, but the deltoid is needed to continue it. Supraspinatus and infraspinatus are supplied by the suprascapular nerve, teres major by the lower subscapular nerve and latissimus dorsi by the thoracodorsal nerve.

In a healthy adult, which part of the nephron reabsorbs the largest fraction of the filtered sodium?

A) Proximal convoluted tubule
B) Descending limb of the loop of Henle
C) Thick ascending limb of the loop of Henle
D) Distal convoluted tubule
E) Collecting duct

Correct answer: A) Proximal convoluted tubule

About two-thirds of filtered sodium is reabsorbed in the proximal tubule, along with water. The thick ascending limb reabsorbs about a quarter, the distal convoluted tubule a smaller share, and the collecting duct fine-tunes the final amount under aldosterone. The descending limb is permeable to water but reabsorbs little sodium.

Statins lower plasma LDL cholesterol by inhibiting the rate-limiting enzyme of cholesterol synthesis. Which enzyme is this?

A) Acetyl-CoA carboxylase
B) HMG-CoA synthase
C) HMG-CoA reductase
D) Lecithin-cholesterol acyltransferase
E) Lipoprotein lipase

Correct answer: C) HMG-CoA reductase

HMG-CoA reductase converts HMG-CoA to mevalonate, the committed and rate-limiting step of cholesterol synthesis. Lower liver cholesterol increases LDL receptor expression, so more LDL is cleared from the blood. Acetyl-CoA carboxylase is the rate-limiting enzyme of fatty acid synthesis, and HMG-CoA synthase acts one step earlier.

A patient on an intravenous infusion of unfractionated heparin develops heavy bleeding, and the activated partial thromboplastin time is markedly prolonged. Which drug reverses the effect of heparin?

A) Vitamin K
B) Protamine sulfate
C) Tranexamic acid
D) Idarucizumab
E) Desmopressin

Correct answer: B) Protamine sulfate

Protamine is strongly basic and binds the acidic heparin molecule, neutralising it. Vitamin K reverses warfarin, idarucizumab reverses dabigatran, tranexamic acid is an antifibrinolytic and desmopressin is used in haemophilia A and von Willebrand disease.

A lung biopsy from a patient with chronic cough and weight loss shows granulomas with Langhans giant cells surrounding a central area of cheese-like, amorphous, granular debris. What type of necrosis is this?

A) Coagulative necrosis
B) Liquefactive necrosis
C) Caseous necrosis
D) Fat necrosis
E) Fibrinoid necrosis

Correct answer: C) Caseous necrosis

Caseous necrosis, with its cheesy appearance and granulomatous rim, is typical of tuberculosis. Coagulative necrosis is seen in infarcts of solid organs, liquefactive necrosis in abscesses and brain infarcts, fat necrosis in acute pancreatitis and breast trauma, and fibrinoid necrosis in blood vessel walls in vasculitis and malignant hypertension.

Which of the following shifts the oxygen-haemoglobin dissociation curve to the right?

A) Alkalosis
B) Hypothermia
C) Increased 2,3-bisphosphoglycerate
D) Carbon monoxide poisoning
E) Fetal haemoglobin

Correct answer: C) Increased 2,3-bisphosphoglycerate

A right shift lowers haemoglobin's affinity for oxygen and helps unload oxygen to the tissues. It is caused by increased 2,3-BPG, carbon dioxide, hydrogen ions (acidosis) and temperature. Alkalosis, hypothermia, carbon monoxide and fetal haemoglobin all shift the curve to the left.

A pudendal nerve block is given for an assisted vaginal delivery, with the ischial spine used as the landmark. From which spinal nerve roots does the pudendal nerve arise?

A) L4–S1
B) L5–S2
C) S1–S3
D) S2–S4
E) S3–S5

Correct answer: D) S2–S4

The pudendal nerve arises from the ventral rami of S2, S3 and S4. It leaves the pelvis through the greater sciatic foramen, passes around the ischial spine and enters the perineum through the lesser sciatic foramen, which is why the ischial spine is the landmark for the block.

During general anaesthesia with sevoflurane and suxamethonium, a patient develops masseter rigidity, a rapidly rising end-tidal carbon dioxide, tachycardia and hyperthermia. Which drug is the specific treatment?

A) Neostigmine
B) Dantrolene
C) Naloxone
D) Flumazenil
E) Sugammadex

Correct answer: B) Dantrolene

This is malignant hyperthermia, triggered by volatile anaesthetics and suxamethonium in susceptible patients. Dantrolene blocks calcium release from the sarcoplasmic reticulum through the ryanodine receptor. Neostigmine and sugammadex reverse neuromuscular blockade, naloxone reverses opioids and flumazenil reverses benzodiazepines.

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