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INI CET practice questions

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Question 1Pre-clinical subjects (Anatomy, Physiology, Biochemistry)

Which nerve is most likely injured in a fracture of the surgical neck of the humerus, causing loss of abduction and deltoid wasting?

  1. Median nerve
  2. Musculocutaneous nerve
  3. Axillary nerve Correct answer.
  4. Radial nerve

Explanation

The axillary nerve winds around the surgical neck of the humerus in the quadrangular space, so fractures at this site injure it. It supplies deltoid and teres minor, and its loss produces weakness of abduction and sensory loss over the lateral shoulder.

Question 2Pre-clinical subjects (Anatomy, Physiology, Biochemistry)

The sinoatrial node initiates the cardiac impulse primarily because its cells exhibit which property?

  1. Spontaneous phase 4 depolarization Correct answer.
  2. Prolonged plateau phase
  3. High resting membrane potassium conductance
  4. Absence of gap junctions

Explanation

Pacemaker cells of the SA node lack a stable resting potential and show spontaneous slow depolarization during phase 4 due to funny current and calcium influx. When threshold is reached, an action potential fires, setting the heart rate.

Question 3Pre-clinical subjects (Anatomy, Physiology, Biochemistry)

A patient with a lesion of the left optic tract will most likely show which visual field defect?

  1. Left homonymous hemianopia
  2. Right homonymous hemianopia Correct answer.
  3. Right superior quadrantanopia
  4. Bitemporal hemianopia

Explanation

The left optic tract carries fibres from the temporal retina of the left eye and nasal retina of the right eye, both representing the right visual field. A complete lesion therefore produces a right homonymous hemianopia.

Question 4Pre-clinical subjects (Anatomy, Physiology, Biochemistry)

Which enzyme catalyses the rate-limiting step of glycolysis?

  1. Hexokinase
  2. Phosphofructokinase-1 Correct answer.
  3. Pyruvate kinase
  4. Aldolase

Explanation

Phosphofructokinase-1 converts fructose-6-phosphate to fructose-1,6-bisphosphate and is the principal rate-limiting, allosterically regulated step of glycolysis. It is activated by AMP and fructose-2,6-bisphosphate and inhibited by ATP and citrate.

Question 5Pre-clinical subjects (Anatomy, Physiology, Biochemistry)

Which vitamin deficiency impairs collagen cross-linking by reducing hydroxylation of proline and lysine residues?

  1. Vitamin D
  2. Vitamin C Correct answer.
  3. Vitamin B12
  4. Vitamin K

Explanation

Vitamin C is a cofactor for prolyl and lysyl hydroxylase, which hydroxylate proline and lysine so that collagen triple helices can form stable cross-links. Deficiency causes scurvy with poor wound healing, bleeding gums and capillary fragility.

Question 6Pre-clinical subjects (Anatomy, Physiology, Biochemistry)

The normal resting membrane potential of a typical skeletal muscle fibre is closest to which value?

  1. 0 mV
  2. -55 mV
  3. +30 mV
  4. -90 mV Correct answer.

Explanation

Skeletal muscle fibres have a high resting potassium permeability, giving a resting membrane potential near -90 mV, close to the potassium equilibrium potential. This negative interior is essential for excitability and propagation of the action potential.

Question 7Pre-clinical subjects (Anatomy, Physiology, Biochemistry)

Which structure passes through the foramen ovale of the sphenoid bone?

  1. Optic nerve
  2. Middle meningeal artery
  3. Maxillary division of the trigeminal nerve
  4. Mandibular division of the trigeminal nerve Correct answer.

Explanation

The foramen ovale transmits the mandibular division of the trigeminal nerve along with the accessory meningeal artery and lesser petrosal nerve. It lies in the greater wing of the sphenoid.

Question 8Pre-clinical subjects (Anatomy, Physiology, Biochemistry)

Which hormone is secreted by the zona glomerulosa of the adrenal cortex?

  1. Aldosterone Correct answer.
  2. Adrenaline
  3. Dehydroepiandrosterone
  4. Cortisol

Explanation

The zona glomerulosa synthesises mineralocorticoids, chiefly aldosterone, under the control of angiotensin II and potassium. Aldosterone promotes sodium reabsorption and potassium secretion in the distal nephron.

Question 9Pre-clinical subjects (Anatomy, Physiology, Biochemistry)

A 45-year-old man has a fasting plasma glucose of 130 mg/dL on two occasions. Which biochemical change best explains the osmotic diuresis seen when glucose exceeds the renal threshold?

  1. Increased aldosterone secretion causes sodium retention
  2. Reduced glomerular filtration rate
  3. Enhanced proximal reabsorption of bicarbonate
  4. Non-reabsorbed glucose in tubular fluid retains water osmotically Correct answer.

Explanation

When filtered glucose exceeds the transport maximum of SGLT carriers, the excess remains in the tubular lumen and exerts osmotic pressure that holds water, producing polyuria. This is the basis of osmotic diuresis in uncontrolled diabetes.

Question 10Pre-clinical subjects (Anatomy, Physiology, Biochemistry)

During a marathon, a runner's muscle uses the purine nucleotide cycle and adenylate kinase. Accumulation of which metabolite most directly stimulates glycolysis via phosphofructokinase-1?

  1. Citrate
  2. AMP Correct answer.
  3. Glucose-6-phosphate
  4. ATP

Explanation

Adenylate kinase converts two ADP molecules to ATP and AMP, and the purine nucleotide cycle also generates AMP. Rising AMP signals low energy charge and allosterically activates phosphofructokinase-1 to increase glycolytic flux.

Question 11Pre-clinical subjects (Anatomy, Physiology, Biochemistry)

A patient has a lesion destroying the left facial nerve within the facial canal just after it exits the stylomastoid foramen. Which combination of signs is expected?

  1. Ipsilateral facial palsy with loss of taste over the anterior tongue
  2. Ipsilateral facial palsy with preserved taste over the anterior tongue Correct answer.
  3. Bilateral facial palsy with loss of corneal reflex
  4. Contralateral facial palsy with hyperacusis

Explanation

The chorda tympani leaves the facial nerve before it exits the stylomastoid foramen, so a lesion distal to that point spares taste from the anterior two-thirds of the tongue. Only the motor branches to facial muscles are affected, giving ipsilateral palsy.

Question 12Pre-clinical subjects (Anatomy, Physiology, Biochemistry)

In the cardiac cycle, which event coincides with the first heart sound?

  1. Atrial systole
  2. Closure of the mitral and tricuspid valves Correct answer.
  3. Closure of the aortic and pulmonary valves
  4. Opening of the mitral and tricuspid valves

Explanation

The first heart sound arises from closure of the atrioventricular valves at the onset of ventricular systole. It marks the boundary between diastole and isovolumetric contraction.

Question 13Pre-clinical subjects (Anatomy, Physiology, Biochemistry)

A newborn presents with projectile non-bilious vomiting at three weeks of age and a palpable olive-shaped mass in the right upper abdomen. Which acid-base disturbance is most likely?

  1. Hyperchloraemic metabolic acidosis
  2. High anion gap metabolic acidosis
  3. Hypochloraemic metabolic alkalosis with hypokalaemia Correct answer.
  4. Respiratory alkalosis

Explanation

Pyloric stenosis causes loss of gastric hydrochloric acid, producing hypochloraemic metabolic alkalosis, and vomiting also causes potassium loss. The kidneys attempt to conserve volume, worsening potassium depletion and maintaining the alkalosis.

Question 14Pre-clinical subjects (Anatomy, Physiology, Biochemistry)

Which muscle is the chief flexor of the hip and is tested by asking the patient to raise the thigh against resistance while supine?

  1. Iliopsoas Correct answer.
  2. Gluteus maximus
  3. Adductor longus
  4. Biceps femoris

Explanation

Iliopsoas, formed by psoas major and iliacus, is the principal hip flexor and is tested by resisted hip flexion with the patient supine. Its action is essential for climbing stairs and rising from a seated position.

Question 15Pre-clinical subjects (Anatomy, Physiology, Biochemistry)

A deficiency of pyruvate dehydrogenase complex most severely impairs which metabolic conversion?

  1. Pyruvate to acetyl-CoA Correct answer.
  2. Phosphoenolpyruvate to pyruvate
  3. Pyruvate to lactate
  4. Oxaloacetate to phosphoenolpyruvate

Explanation

Pyruvate dehydrogenase catalyses the irreversible oxidative decarboxylation of pyruvate to acetyl-CoA, linking glycolysis to the citric acid cycle. Deficiency causes lactate accumulation and neurological impairment because acetyl-CoA cannot be generated aerobically.

Question 16Pre-clinical subjects (Anatomy, Physiology, Biochemistry)

Which cells of the gastric mucosa secrete intrinsic factor?

  1. Chief cells
  2. Mucous neck cells
  3. Parietal cells Correct answer.
  4. G cells

Explanation

Parietal cells secrete hydrochloric acid and intrinsic factor, which is required for ileal absorption of vitamin B12. Loss of parietal cells in pernicious anaemia therefore causes B12 deficiency and megaloblastic anaemia.

Question 17Pre-clinical subjects (Anatomy, Physiology, Biochemistry)

A patient with chronic kidney disease has a plasma potassium of 6.2 mmol/L. Which ECG change is most characteristic of hyperkalaemia?

  1. Delta waves
  2. Prominent U waves
  3. Prolonged QT interval
  4. Tall peaked T waves Correct answer.

Explanation

Hyperkalaemia initially produces tall, narrow-based peaked T waves, and severe elevation can progress to widened QRS complexes and sine-wave patterns. The change reflects accelerated repolarization as the potassium gradient across the membrane falls.

Question 18Pre-clinical subjects (Anatomy, Physiology, Biochemistry)

In the brain, the main route for reutilization of ammonia into glutamate involves which reaction?

  1. Transamination of oxaloacetate
  2. Reductive amination of alpha-ketoglutarate Correct answer.
  3. Decarboxylation of glutamate
  4. Deamination of glutamine

Explanation

Glutamate dehydrogenase catalyses the reductive amination of alpha-ketoglutarate with ammonia and NADPH, forming glutamate. This reaction is central to ammonia detoxification in brain and liver and links amino acid metabolism to the citric acid cycle.

Question 19Pre-clinical subjects (Anatomy, Physiology, Biochemistry)

Which cranial nerve provides parasympathetic secretomotor supply to the parotid gland?

  1. Facial nerve
  2. Trigeminal nerve
  3. Glossopharyngeal nerve Correct answer.
  4. Vagus nerve

Explanation

Preganglionic parasympathetic fibres from the glossopharyngeal nerve travel via the lesser petrosal nerve to the otic ganglion, whose postganglionic fibres reach the parotid gland. The facial nerve supplies the submandibular and sublingual glands instead.

Question 20Pre-clinical subjects (Anatomy, Physiology, Biochemistry)

A 60-year-old man develops sudden painless loss of vision in one eye with a pale retina and a cherry-red spot at the macula. Which artery is occluded?

  1. Ophthalmic vein
  2. Central retinal artery Correct answer.
  3. Posterior cerebral artery
  4. Central retinal vein

Explanation

Occlusion of the central retinal artery causes ischaemic whitening of the inner retina, while the fovea remains red because its blood supply comes from the choroid. This produces the classic cherry-red spot with sudden painless visual loss.

Question 21Pre-clinical subjects (Anatomy, Physiology, Biochemistry)

Which statement best explains why the oxygen-haemoglobin dissociation curve shifts to the right during exercise?

  1. Increased 2,3-BPG decreases oxygen unloading
  2. Increased carbon dioxide and hydrogen ions reduce haemoglobin oxygen affinity Correct answer.
  3. Reduced temperature increases oxygen unloading
  4. Increased pH raises haemoglobin oxygen affinity

Explanation

Exercising muscle produces carbon dioxide and hydrogen ions, and the resulting fall in pH and rise in temperature reduce haemoglobin's affinity for oxygen. This Bohr effect facilitates oxygen unloading where it is most needed.

Question 22Pre-clinical subjects (Anatomy, Physiology, Biochemistry)

A mutation abolishes the activity of ornithine transcarbamoylase. Which finding is most expected in this patient?

  1. Hypoammonaemia with increased urinary urea
  2. Hyperammonaemia with decreased urinary orotic acid
  3. Hyperammonaemia with increased urinary orotic acid Correct answer.
  4. Hyperammonaemia with increased urinary citrulline

Explanation

Ornithine transcarbamoylase deficiency blocks carbamoyl phosphate use in the urea cycle, so carbamoyl phosphate accumulates and spills into pyrimidine synthesis, raising orotic acid excretion. Ammonia rises because the cycle cannot proceed, producing encephalopathy.

Question 23Pre-clinical subjects (Anatomy, Physiology, Biochemistry)

A patient has a lesion at the level of the T4 spinal cord segment. Which pattern of motor and sensory findings is most consistent?

  1. Flaccid paraplegia with preserved proprioception below T4
  2. Ipsilateral loss of vibration with contralateral spasticity
  3. Spastic paraplegia with loss of pain and temperature below the T4 dermatome Correct answer.
  4. Sacral sparing with perianal sensory loss only

Explanation

A complete cord lesion above the lumbar enlargement interrupts corticospinal and spinothalamic tracts, producing spastic paraplegia and a sensory level for pain and temperature at and below T4. Upper motor neuron signs appear after the initial period of spinal shock.

Question 24Pre-clinical subjects (Anatomy, Physiology, Biochemistry)

A 30-year-old woman has muscle cramps and weakness after exercise, with a normal resting serum potassium that falls during attacks. Which channel defect best explains this pattern?

  1. Loss-of-function mutation in the skeletal muscle chloride channel Correct answer.
  2. Gain-of-function mutation in the skeletal muscle sodium channel
  3. Impaired calcium release from the sarcoplasmic reticulum
  4. Defect in the acetylcholine receptor at the motor end plate

Explanation

Hypokalaemic periodic paralysis results from loss-of-function mutations in the skeletal muscle chloride channel, which reduce membrane chloride conductance and destabilize the resting potential. Attacks are triggered by carbohydrate meals or rest after exercise and improve with potassium.

Question 25Pre-clinical subjects (Anatomy, Physiology, Biochemistry)

A patient with a gastrocnemius tear is examined for ankle reflexes. Which nerve root is primarily being tested by the ankle jerk?

  1. L2
  2. S1 Correct answer.
  3. L5
  4. L4

Explanation

The ankle jerk tests the S1 reflex arc through the tibial nerve, with the gastrocnemius and soleus as the effector muscles. Its loss suggests an S1 radiculopathy or tibial nerve lesion.

Question 26Pre-clinical subjects (Anatomy, Physiology, Biochemistry)

A 24-year-old man is examined after a road traffic accident. He has lost sensation over the tip of the shoulder and the lateral aspect of the upper arm, and the deltoid is wasted. Which part of the brachial plexus is most likely injured?

  1. Upper trunk Correct answer.
  2. Lower trunk
  3. Medial cord
  4. Posterior cord

Explanation

The upper trunk (C5-C6) gives the suprascapular nerve and the lateral pectoral contribution, and its fibres form the axillary nerve, so lesions produce the Erb pattern of deltoid weakness, loss of shoulder-tip sensation and a waiter's-tip posture. The lower trunk (C8-T1) instead causes wasting of the small muscles of the hand with ulnar-sided sensory loss.

Question 27Pre-clinical subjects (Anatomy, Physiology, Biochemistry)

Which structure forms the lateral boundary of the epiploic foramen (foramen of Winslow)?

  1. The hepatoduodenal ligament Correct answer.
  2. The caudate lobe of the liver
  3. The portal vein
  4. The inferior vena cava

Explanation

The epiploic foramen is bounded anteriorly by the free edge of the lesser omentum, the hepatoduodenal ligament, which contains the portal triad. Posteriorly lies the inferior vena cava, superiorly the caudate lobe, and inferiorly the first part of the duodenum.

Question 28Pre-clinical subjects (Anatomy, Physiology, Biochemistry)

During a voluntary contraction, which sequence of events at the neuromuscular junction directly triggers the muscle action potential?

  1. Release of acetylcholine causes direct opening of voltage-gated sodium channels in the endplate membrane
  2. Binding of acetylcholine to nicotinic receptors opens cation channels and depolarises the endplate to threshold Correct answer.
  3. Calcium influx into the muscle fibre triggers calcium release from the sarcoplasmic reticulum
  4. Acetylcholine activates muscarinic receptors that raise intracellular cyclic AMP

Explanation

Acetylcholine released from the motor nerve terminal binds nicotinic receptors on the motor endplate; these are ligand-gated cation channels whose opening produces the endplate potential, which depolarises adjacent membrane to threshold and fires a muscle action potential. Calcium-induced calcium release occurs later, during excitation-contraction coupling.

Question 29Pre-clinical subjects (Anatomy, Physiology, Biochemistry)

Which enzyme catalyses the committed, rate-limiting step in cholesterol biosynthesis?

  1. Squalene epoxidase
  2. Mevalonate kinase
  3. HMG-CoA synthase
  4. HMG-CoA reductase Correct answer.

Explanation

HMG-CoA reductase converts HMG-CoA to mevalonate and is the committed, rate-limiting step of cholesterol synthesis; it is the target of statins and is regulated by sterol-mediated feedback. The other enzymes act later in the pathway and are not the principal regulatory point.

Question 30Pre-clinical subjects (Anatomy, Physiology, Biochemistry)

A 55-year-old woman with longstanding hypertension presents with proximal muscle weakness, polyuria and hypokalaemia. Plasma renin activity is low and aldosterone is high. Which biochemical finding best fits an aldosterone-secreting adrenal adenoma?

  1. Metabolic acidosis with elevated plasma renin
  2. Hyperkalaemia with suppressed aldosterone
  3. Hypoglycaemia with elevated insulin
  4. Metabolic alkalosis with suppressed plasma renin Correct answer.

Explanation

Primary hyperaldosteronism causes sodium retention, potassium and hydrogen loss, producing hypokalaemic metabolic alkalosis while the expanded volume suppresses renin. Secondary hyperaldosteronism instead shows high renin with normal or low aldosterone.

Question 31Pre-clinical subjects (Anatomy, Physiology, Biochemistry)

Which nerve is most likely injured in a midshaft fracture of the humerus, and which movement is then chiefly lost?

  1. Radial nerve, with loss of wrist extension Correct answer.
  2. Median nerve, with loss of thumb opposition
  3. Axillary nerve, with loss of shoulder abduction
  4. Ulnar nerve, with loss of finger abduction

Explanation

The radial nerve runs in the spiral groove against the humeral shaft, so midshaft fractures commonly injure it, producing wrist drop and weakness of finger extension. The axillary nerve is at risk in surgical neck fractures, and the median and ulnar nerves are not directly related to the shaft.

Question 32Pre-clinical subjects (Anatomy, Physiology, Biochemistry)

In the fasting state, which enzyme is primarily responsible for releasing free fatty acids from adipose triacylglycerol stores?

  1. Lipoprotein lipase
  2. Hormone-sensitive lipase Correct answer.
  3. Acetyl-CoA carboxylase
  4. Pancreatic lipase

Explanation

Hormone-sensitive lipase in adipocytes is activated by glucagon and catecholamines through cyclic AMP-dependent phosphorylation and hydrolyses stored triacylglycerol, releasing fatty acids and glycerol. Lipoprotein lipase acts on circulating lipoproteins at capillary endothelium, while pancreatic lipase digests dietary fat in the gut.

Question 33Pre-clinical subjects (Anatomy, Physiology, Biochemistry)

A patient is given a drug that blocks the Na+/K+-ATPase of the thick ascending limb. Which change in tubular fluid is most expected?

  1. Increased hydrogen secretion with metabolic alkalosis
  2. Increased sodium and potassium concentration with reduced medullary interstitial osmolality Correct answer.
  3. Increased glucose reabsorption with glycosuria
  4. Increased sodium reabsorption with concentrated urine

Explanation

The Na+/K+/2Cl- cotransporter of the thick ascending limb depends on the basolateral sodium gradient set by Na+/K+-ATPase; blocking the pump reduces salt reabsorption, raising luminal sodium and potassium and lowering the medullary osmotic gradient, so concentrating ability falls. This is the basis of loop diuretic action.

Question 34Pre-clinical subjects (Anatomy, Physiology, Biochemistry)

Which ascending tract carries fine touch and conscious proprioception from the lower limb and where does it decussate?

  1. Dorsal column, decussating in the medulla Correct answer.
  2. Corticospinal tract, decussating in the midbrain
  3. Spinothalamic tract, decussating within the spinal cord
  4. Spinocerebellar tract, decussating in the cerebellum

Explanation

Fine touch and conscious proprioception from the lower limb travel in the fasciculus gracilis, synapse in the nucleus gracilis, and cross in the medulla as internal arcuate fibres to form the medial lemniscus. The spinothalamic tract instead crosses within the spinal cord close to its segment of entry.

Question 35Pre-clinical subjects (Anatomy, Physiology, Biochemistry)

In the urea cycle, which reaction occurs within the mitochondrial matrix?

  1. Conversion of argininosuccinate to arginine and fumarate
  2. Conversion of ornithine and carbamoyl phosphate to citrulline Correct answer.
  3. Cleavage of fumarate to malate
  4. Hydrolysis of arginine to ornithine and urea

Explanation

Ornithine transcarbamoylase, located in the mitochondrial matrix, condenses ornithine with carbamoyl phosphate to form citrulline, which then leaves the mitochondrion. The remaining reactions of the cycle occur in the cytosol.

Question 36Pre-clinical subjects (Anatomy, Physiology, Biochemistry)

Which change in lung mechanics best explains the increased work of breathing in a patient with pulmonary fibrosis?

  1. Reduced compliance with increased elastic recoil Correct answer.
  2. Increased airway resistance with normal compliance
  3. Increased compliance with reduced elastic recoil
  4. Reduced surface tension with alveolar collapse

Explanation

Fibrosis stiffens the lung interstitium, lowering compliance and increasing elastic recoil, so greater transpulmonary pressure is needed for the same volume change. Emphysema produces the opposite pattern of increased compliance and reduced recoil.

Question 37Pre-clinical subjects (Anatomy, Physiology, Biochemistry)

A 3-day-old neonate develops lethargy, vomiting and hyperammonaemia after feeding. Plasma citrulline is very low and urinary orotic acid is markedly increased. Which enzyme deficiency is most likely?

  1. N-acetylglutamate synthase
  2. Argininosuccinate lyase
  3. Carbamoyl phosphate synthetase I
  4. Ornithine transcarbamoylase Correct answer.

Explanation

Ornithine transcarbamoylase deficiency blocks condensation of carbamoyl phosphate with ornithine, so carbamoyl phosphate accumulates and is shunted into pyrimidine synthesis, raising orotic acid, while citrulline is low. Proximal defects such as carbamoyl phosphate synthetase I deficiency produce low orotic acid.

Question 38Pre-clinical subjects (Anatomy, Physiology, Biochemistry)

Which hormone is the principal regulator of plasma calcium in response to a fall in ionised calcium?

  1. Insulin
  2. Parathyroid hormone Correct answer.
  3. Aldosterone
  4. Calcitonin

Explanation

Parathyroid hormone is released when ionised calcium falls and acts on bone, kidney and, indirectly through calcitriol, the gut to restore calcium. Calcitonin lowers calcium and is not the main defence against hypocalcaemia in humans.

Question 39Pre-clinical subjects (Anatomy, Physiology, Biochemistry)

A 60-year-old man has a lesion of the right recurrent laryngeal nerve after thyroid surgery. Which finding is most expected?

  1. Deviation of the uvula to the left on phonation
  2. Loss of sensation over the right external ear
  3. Complete loss of taste over the posterior third of the tongue
  4. Hoarseness with the right vocal cord in a paramedian position Correct answer.

Explanation

The recurrent laryngeal nerve supplies all intrinsic laryngeal muscles except cricothyroid, so unilateral injury leaves the cord paralysed and the voice hoarse. Taste over the posterior tongue and palatal movement are carried by the glossopharyngeal and vagal pharyngeal branches, not the recurrent nerve.

Question 40Pre-clinical subjects (Anatomy, Physiology, Biochemistry)

Which statement about the cardiac action potential of ventricular muscle is correct?

  1. Repolarisation is caused by opening of funny channels
  2. The resting potential is maintained mainly by calcium leak
  3. The plateau phase results from balanced calcium influx and potassium efflux Correct answer.
  4. The rapid upstroke results from chloride influx

Explanation

In ventricular myocytes the plateau reflects a slow inward calcium current through L-type channels balanced against outward potassium currents, prolonging the action potential and the refractory period. The upstroke is due to fast sodium entry, and the resting potential depends largely on potassium permeability.

Question 41Pre-clinical subjects (Anatomy, Physiology, Biochemistry)

Which structural feature distinguishes a typical medium-sized artery from a muscular arteriole?

  1. Multiple layers of smooth muscle in the tunica media Correct answer.
  2. Absence of an internal elastic lamina
  3. Presence of valves in the lumen
  4. A single endothelial layer with no media

Explanation

Medium arteries have a well-developed tunica media containing several layers of smooth muscle between distinct elastic laminae, whereas arterioles have only one or two smooth muscle layers. This difference underlies their different roles in distributing versus resisting blood flow.

Question 42Pre-clinical subjects (Anatomy, Physiology, Biochemistry)

Which vitamin deficiency impairs the conversion of prothrombin to its active form by reducing gamma-carboxylation of glutamate residues?

  1. Vitamin K Correct answer.
  2. Cobalamin
  3. Vitamin C
  4. Thiamine

Explanation

Vitamin K is the cofactor for gamma-glutamyl carboxylase, which converts glutamate residues on clotting factors II, VII, IX and X into gamma-carboxyglutamate, enabling calcium-dependent binding to phospholipid membranes. Its deficiency therefore prolongs prothrombin time.

Question 43Pre-clinical subjects (Anatomy, Physiology, Biochemistry)

A patient with a cerebellar lesion is asked to touch the tip of the nose. Which abnormality is most characteristic of a lesion of the right cerebellar hemisphere?

  1. Past-pointing and intention tremor of the right arm Correct answer.
  2. Resting tremor of both hands
  3. Spastic weakness of the right arm
  4. Loss of pain sensation in the right hand

Explanation

The cerebellar hemispheres control the ipsilateral limbs, so a right hemisphere lesion produces dysmetria, past-pointing and intention tremor of the right arm. Weakness and sensory loss reflect corticospinal or spinothalamic damage, and resting tremor is extrapyramidal.

Question 44Pre-clinical subjects (Anatomy, Physiology, Biochemistry)

Which mechanism best explains the increased oxygen unloading by haemoglobin in exercising skeletal muscle?

  1. Falling 2,3-bisphosphoglycerate increases oxygen affinity
  2. Rising temperature and carbon dioxide lower haemoglobin oxygen affinity Correct answer.
  3. Reduced carbon dioxide raises the P50
  4. Rising pH increases haemoglobin oxygen affinity

Explanation

Exercise raises temperature, carbon dioxide and hydrogen ion concentration, all of which shift the oxygen-haemoglobin dissociation curve to the right, reducing affinity and enhancing unloading at tissue level. This is the Bohr effect and related temperature effect.

Question 45Pre-clinical subjects (Anatomy, Physiology, Biochemistry)

Which feature of the fetal circulation allows oxygenated blood from the umbilical vein to bypass the hepatic sinusoids and reach the inferior vena cava?

  1. Ductus venosus Correct answer.
  2. Ductus arteriosus
  3. Foramen ovale
  4. Umbilical arteries

Explanation

The ductus venosus shunts oxygenated umbilical blood directly from the left branch of the portal vein into the inferior vena cava, bypassing the liver. The ductus arteriosus and foramen ovale shunt blood within the heart and great vessels after it has reached the right side.

Question 46Pre-clinical subjects (Anatomy, Physiology, Biochemistry)

Which step of glycolysis is the main site of regulation by phosphofructokinase-1?

  1. Conversion of glucose to glucose-6-phosphate
  2. Phosphorylation of fructose-6-phosphate to fructose-1,6-bisphosphate Correct answer.
  3. Conversion of phosphoenolpyruvate to pyruvate
  4. Conversion of 3-phosphoglycerate to 2-phosphoglycerate

Explanation

Phosphofructokinase-1 catalyses the phosphorylation of fructose-6-phosphate and is the committed, rate-limiting step of glycolysis, activated by AMP and fructose-2,6-bisphosphate and inhibited by ATP and citrate. Hexokinase and pyruvate kinase are also regulated but are not the principal flux-controlling step.

Question 47Pre-clinical subjects (Anatomy, Physiology, Biochemistry)

A young woman has a lesion of the left hypoglossal nerve. On protrusion of the tongue, which finding is expected?

  1. There is loss of taste on the left side
  2. The tongue deviates to the left Correct answer.
  3. The tongue cannot be elevated
  4. The tongue deviates to the right

Explanation

The genioglossus muscle, supplied by the hypoglossal nerve, protrudes the tongue; with a left-sided lesion the unaffected right genioglossus pushes the tongue towards the paralysed left side. Taste is carried by the facial and glossopharyngeal nerves, not the hypoglossal.

Question 48Pre-clinical subjects (Anatomy, Physiology, Biochemistry)

Which factor most directly determines the filtration fraction in the glomerulus?

  1. The ratio of afferent to efferent arteriolar resistance
  2. The ratio of filtered sodium to excreted sodium
  3. The ratio of glomerular filtration rate to renal plasma flow Correct answer.
  4. The ratio of renal plasma flow to cardiac output

Explanation

Filtration fraction is defined as glomerular filtration rate divided by renal plasma flow, normally about 0.2. Changes in arteriolar resistance alter both variables and so influence the fraction indirectly, but the definition is the ratio itself.

Question 49Pre-clinical subjects (Anatomy, Physiology, Biochemistry)

Which muscle of the rotator cuff is chiefly responsible for initiating abduction of the arm in the first 15 degrees?

  1. Infraspinatus
  2. Supraspinatus Correct answer.
  3. Subscapularis
  4. Teres minor

Explanation

Supraspinatus initiates abduction during the first 15 degrees before the deltoid becomes the dominant abductor. Infraspinatus and teres minor are lateral rotators, and subscapularis is a medial rotator.

Question 50Pre-clinical subjects (Anatomy, Physiology, Biochemistry)

A patient is given a competitive inhibitor of the enzyme dihydrofolate reductase. Which change in enzyme kinetics is expected?

  1. Increased Michaelis constant with unchanged maximum velocity Correct answer.
  2. Reduced maximum velocity with unchanged Michaelis constant
  3. Reduced maximum velocity and reduced Michaelis constant
  4. Unchanged Michaelis constant and increased maximum velocity

Explanation

A competitive inhibitor binds reversibly at the active site, so more substrate is needed to reach half-maximal velocity, raising the apparent Michaelis constant, but sufficiently high substrate can displace the inhibitor and restore the maximum velocity. Non-competitive inhibition instead lowers maximum velocity.