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MECEE-PG Nepal study materials
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MECEE-PG Nepal practice questions

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

Which muscle of the rotator cuff is chiefly responsible for initiating abduction of the arm at the shoulder joint?

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

Explanation

The supraspinatus arises from the supraspinous fossa and its tendon passes under the acromion to insert on the greater tubercle, where it initiates the first 15 degrees of abduction before the deltoid takes over. The other cuff muscles act mainly as medial or lateral rotators and depressors of the humeral head.

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

A lesion of the axillary nerve following a surgical neck fracture of the humerus would most directly impair which movement?

  1. Flexion of the elbow
  2. Opposition of the thumb
  3. Abduction of the arm Correct answer.
  4. Extension of the wrist

Explanation

The axillary nerve supplies the deltoid and teres minor, so its injury weakens abduction and lateral rotation of the shoulder. Elbow flexion, wrist extension, and thumb opposition are served by other nerves (musculocutaneous, radial, and median respectively).

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

Which cranial nerve provides motor innervation to the muscles of mastication?

  1. Glossopharyngeal nerve
  2. Facial nerve
  3. Hypoglossal nerve
  4. Mandibular division of the trigeminal nerve Correct answer.

Explanation

The mandibular division of the trigeminal nerve (V3) carries branchial motor fibers to the muscles of mastication, including masseter, temporalis, and pterygoids. The facial nerve supplies muscles of facial expression, and the hypoglossal nerve supplies the tongue.

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

The structure that passes through the foramen ovale is the

  1. Middle meningeal artery
  2. Optic nerve
  3. Mandibular nerve Correct answer.
  4. Maxillary nerve

Explanation

The foramen ovale transmits the mandibular division of the trigeminal nerve along with the accessory meningeal artery and lesser petrosal nerve. The maxillary nerve passes through the foramen rotundum, and the middle meningeal artery enters via the foramen spinosum.

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

Which part of the nephron is the principal site of regulated water reabsorption under the influence of antidiuretic hormone?

  1. Proximal convoluted tubule
  2. Distal convoluted tubule
  3. Thin descending limb of the loop of Henle
  4. Collecting duct Correct answer.

Explanation

Antidiuretic hormone inserts aquaporin-2 channels into the apical membrane of collecting duct principal cells, allowing regulated water reabsorption driven by the medullary osmotic gradient. The proximal tubule reabsorbs most water but in an unregulated, obligatory fashion.

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

In the cardiac cycle, the first heart sound is produced by

  1. Opening of the atrioventricular valves
  2. Rapid ventricular filling
  3. Closure of the semilunar valves
  4. Closure of the atrioventricular valves Correct answer.

Explanation

The first heart sound marks the onset of ventricular systole and is generated by closure of the mitral and tricuspid valves. Semilunar valve closure produces the second sound, while rapid filling produces the third sound.

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

A patient has a resting membrane potential of about -90 mV in a ventricular myocyte. Which ion contributes most to setting this resting potential?

  1. Potassium Correct answer.
  2. Chloride
  3. Calcium
  4. Sodium

Explanation

At rest, the membrane is most permeable to potassium through inward-rectifier channels, so the resting potential approaches the potassium equilibrium potential. Sodium and calcium permeabilities are low at rest, and chloride contributes only modestly.

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

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

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

Explanation

The zona glomerulosa synthesizes aldosterone under the control of angiotensin II and potassium. Cortisol comes from the zona fasciculata, androgens from the zona reticularis, and adrenaline from the adrenal medulla.

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

Surfactant in the pulmonary alveoli is primarily secreted by

  1. Alveolar macrophages
  2. Type II pneumocytes Correct answer.
  3. Type I pneumocytes
  4. Clara cells

Explanation

Type II pneumocytes synthesize and secrete surfactant, which lowers alveolar surface tension and prevents collapse. Type I pneumocytes form the thin gas-exchange barrier and do not secrete surfactant.

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

Which of the following best describes the Bohr effect?

  1. A rise in carbon dioxide shifts the oxygen dissociation curve to the right Correct answer.
  2. A fall in temperature shifts the oxygen dissociation curve to the right
  3. A rise in pH shifts the oxygen dissociation curve to the right
  4. A rise in 2,3-BPG shifts the oxygen dissociation curve to the left

Explanation

Increased carbon dioxide lowers pH and promotes unloading of oxygen by shifting the dissociation curve to the right. This rightward shift reflects reduced hemoglobin oxygen affinity in metabolically active tissues.

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

The normal renal threshold for glucose is approximately

  1. 50 mg/dL
  2. 100 mg/dL
  3. 180 mg/dL Correct answer.
  4. 300 mg/dL

Explanation

Glucose is reabsorbed by SGLT transporters until the filtered load exceeds their transport maximum, which occurs at a plasma glucose of about 180 mg/dL. Above this threshold, glucose appears in the urine.

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

Which enzyme catalyzes the rate-limiting step of glycolysis?

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

Explanation

Phosphofructokinase-1 catalyzes the committed, rate-limiting step of glycolysis by phosphorylating fructose-6-phosphate. It is allosterically regulated by ATP, citrate, AMP, and fructose-2,6-bisphosphate.

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

In the urea cycle, which enzyme catalyzes the rate-limiting step?

  1. Argininosuccinate lyase
  2. Arginase
  3. Carbamoyl phosphate synthetase I Correct answer.
  4. Ornithine transcarbamoylase

Explanation

Carbamoyl phosphate synthetase I catalyzes the first, rate-limiting reaction of the urea cycle and is activated by N-acetylglutamate. It is located in the mitochondrial matrix.

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

A deficiency of vitamin B1 (thiamine) most directly impairs which enzyme complex?

  1. Lactate dehydrogenase
  2. Hexokinase
  3. Pyruvate kinase
  4. Pyruvate dehydrogenase Correct answer.

Explanation

Thiamine pyrophosphate is a coenzyme for pyruvate dehydrogenase, alpha-ketoglutarate dehydrogenase, and transketolase. Its deficiency impairs oxidative decarboxylation of pyruvate and leads to lactic acidosis and neurological dysfunction.

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

The enzyme deficient in classic phenylketonuria is

  1. Branched-chain ketoacid dehydrogenase
  2. Homogentisate oxidase
  3. Tyrosinase
  4. Phenylalanine hydroxylase Correct answer.

Explanation

Classic phenylketonuria results from deficiency of phenylalanine hydroxylase, which converts phenylalanine to tyrosine. Untreated, the resulting hyperphenylalaninemia causes intellectual disability.

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

Which lipoprotein is richest in triglycerides among the following?

  1. Low-density lipoprotein
  2. Chylomicrons Correct answer.
  3. Low-density lipoprotein and high-density lipoprotein equally
  4. High-density lipoprotein

Explanation

Chylomicrons are the largest lipoproteins and carry the highest proportion of triglycerides, reflecting their role in transporting dietary fat. LDL and HDL are relatively triglyceride-poor and cholesterol-rich.

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

A competitive inhibitor of an enzyme causes which change in the Michaelis-Menten kinetics?

  1. A decrease in both Km and Vmax
  2. An increase in both Km and Vmax
  3. A decrease in Vmax with unchanged Km
  4. An increase in apparent Km with unchanged Vmax Correct answer.

Explanation

A competitive inhibitor binds reversibly to the active site, raising the apparent Km because more substrate is needed to reach half-maximal velocity, while Vmax is unchanged at saturating substrate. Noncompetitive inhibition instead lowers Vmax without changing Km.

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

In DNA replication, which enzyme removes the RNA primer and replaces it with DNA?

  1. Helicase
  2. DNA polymerase I Correct answer.
  3. Primase
  4. DNA polymerase III

Explanation

DNA polymerase I uses its 5'-to-3' exonuclease activity to remove RNA primers and its polymerase activity to fill the gaps with DNA. DNA polymerase III performs the bulk of chain elongation.

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

Which of the following is a ketone body produced by the liver?

  1. Beta-hydroxybutyrate Correct answer.
  2. Glycerol
  3. Lactate
  4. Pyruvate

Explanation

The liver produces acetoacetate and beta-hydroxybutyrate from acetyl-CoA during prolonged fasting, and these are exported to peripheral tissues as fuel. Lactate, pyruvate, and glycerol are not ketone bodies.

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

In the pentose phosphate pathway, the enzyme that generates NADPH is

  1. Ribulose-5-phosphate epimerase
  2. Transketolase
  3. Glucose-6-phosphate dehydrogenase Correct answer.
  4. Phosphoglucose isomerase

Explanation

Glucose-6-phosphate dehydrogenase catalyzes the oxidative, rate-limiting step that reduces NADP+ to NADPH. Transketolase and epimerase act in the non-oxidative phase, and phosphoglucose isomerase converts glucose-6-phosphate to fructose-6-phosphate.

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

Which muscle forms the anterior wall of the inguinal canal?

  1. External oblique aponeurosis Correct answer.
  2. Internal oblique muscle fibers
  3. Fascia transversalis
  4. Transversus abdominis

Explanation

The anterior wall of the inguinal canal is formed mainly by the external oblique aponeurosis, reinforced laterally by internal oblique. The posterior wall is formed by fascia transversalis and the conjoint tendon, while the roof is formed by arching fibers of internal oblique and transversus abdominis.

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

The portal vein is formed by the union of

  1. Inferior mesenteric and splenic veins
  2. Superior mesenteric and splenic veins Correct answer.
  3. Hepatic veins and inferior vena cava
  4. Left and right gastric veins

Explanation

The portal vein is formed behind the neck of the pancreas by the union of the superior mesenteric and splenic veins. The inferior mesenteric vein usually drains into the splenic vein rather than joining at the origin.

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

Which cranial nerve is responsible for the gag reflex afferent limb?

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

Explanation

The glossopharyngeal nerve carries general sensation from the posterior third of the tongue and pharynx, forming the afferent limb of the gag reflex, while the vagus provides the efferent limb. Testing the gag reflex therefore assesses both nerves.

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

The largest tarsal bone, which transmits body weight to the calcaneus, is the

  1. Calcaneus
  2. Cuboid
  3. Navicular
  4. Talus Correct answer.

Explanation

The talus is the largest tarsal bone and articulates above with the tibia and fibula and below with the calcaneus, transmitting body weight. The calcaneus is the largest tarsal bone in volume but is distal to the talus in the weight-bearing chain.

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

Which of the following is a function of the spleen most relevant to hematology?

  1. Production of bile
  2. Removal of aged red blood cells Correct answer.
  3. Storage of vitamin B12
  4. Secretion of erythropoietin

Explanation

The spleen acts as a filter for the blood, removing aged or damaged red blood cells through its red pulp macrophages. Erythropoietin is produced mainly by the kidneys, and bile is produced by the liver.

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

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

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

Explanation

The foramen ovale transmits the mandibular division (V3) of the trigeminal nerve along with the accessory meningeal artery and lesser petrosal nerve. The maxillary division passes through the foramen rotundum, the optic nerve through the optic canal, and the middle meningeal artery through the foramen spinosum.

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

A 45-year-old man sustains a fracture of the surgical neck of the humerus. Which nerve is most likely injured?

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

Explanation

The axillary nerve winds around the surgical neck of the humerus in the quadrangular space, so fractures at this site commonly injure it, producing deltoid weakness and sensory loss over the lateral shoulder. The radial nerve lies in the spiral groove of the shaft, while the median and musculocutaneous nerves are not related to the surgical neck.

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

Which type of cartilage forms the epiphyseal plate and provides a model for endochondral ossification?

  1. Elastic cartilage
  2. Hyaline cartilage Correct answer.
  3. Reticular cartilage
  4. Fibrocartilage

Explanation

Hyaline cartilage forms the epiphyseal growth plate and serves as the provisional template that is progressively replaced by bone during endochondral ossification. Fibrocartilage forms the intervertebral discs and elastic cartilage forms the external ear and epiglottis.

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

Occlusion of the anterior interventricular branch of the left coronary artery most directly compromises which region of the heart?

  1. Posterior wall of the left ventricle
  2. Sinoatrial node
  3. Right atrium
  4. Anterior wall of the left ventricle Correct answer.

Explanation

The anterior interventricular (left anterior descending) artery supplies the anterior two-thirds of the interventricular septum and the anterior wall of the left ventricle. The posterior wall is generally supplied by the posterior interventricular branch of the right coronary artery.

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

During quiet expiration, which change occurs in the alveoli relative to atmospheric pressure?

  1. Alveolar pressure rises above atmospheric pressure Correct answer.
  2. Alveolar pressure becomes strongly negative
  3. Alveolar pressure falls below atmospheric pressure
  4. Alveolar pressure remains equal to pleural pressure

Explanation

Quiet expiration is passive: elastic recoil raises alveolar pressure slightly above atmospheric pressure, driving air out until pressures equalize. Alveolar pressure below atmospheric occurs during inspiration, when the thoracic cavity expands.

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

Which factor most increases the oxygen affinity of hemoglobin?

  1. Increased 2,3-BPG concentration
  2. Decreased carbon dioxide Correct answer.
  3. Increased temperature
  4. Decreased pH

Explanation

A fall in carbon dioxide reduces carbamino formation and raises pH, both of which shift the oxygen dissociation curve to the left and increase hemoglobin's affinity for oxygen. Raised temperature, increased 2,3-BPG, and acidosis all reduce affinity.

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

Which segment of the nephron is the principal site of regulated water reabsorption under the influence of antidiuretic hormone?

  1. Ascending thick limb of the loop of Henle
  2. Proximal convoluted tubule
  3. Collecting duct Correct answer.
  4. Thin descending limb of the loop of Henle

Explanation

Antidiuretic hormone inserts aquaporin-2 channels into the apical membrane of collecting duct principal cells, allowing regulated water reabsorption. The proximal tubule reabsorbs water constitutively, and the ascending limb is relatively water-impermeable.

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

Which hormone is the principal regulator of calcium homeostasis by increasing bone resorption and renal calcium reabsorption?

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

Explanation

Parathyroid hormone raises serum calcium by stimulating osteoclastic bone resorption, increasing distal tubular calcium reabsorption, and promoting renal activation of vitamin D. Calcitonin has the opposite effect by inhibiting osteoclasts.

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

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

  1. Right homonymous hemianopia
  2. Total blindness of the right eye
  3. Left homonymous hemianopia Correct answer.
  4. Bitemporal hemianopia

Explanation

The right optic tract carries fibers from the temporal retina of the right eye and the nasal retina of the left eye, both of which subserve the left visual field. A lesion therefore produces a left homonymous hemianopia. Chiasmal lesions produce bitemporal defects.

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

Which spinal tract carries fine touch and conscious proprioception from the lower limb and decussates in the medulla?

  1. Dorsal column-medial lemniscus pathway Correct answer.
  2. Ventral corticospinal tract
  3. Lateral spinothalamic tract
  4. Anterior spinocerebellar tract

Explanation

The dorsal column-medial lemniscus pathway transmits discriminative touch, vibration, and conscious proprioception and crosses in the medulla as internal arcuate fibers. The spinothalamic tract carries pain and temperature and crosses within the spinal cord.

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

Which enzyme catalyzes the committed step of cholesterol biosynthesis?

  1. HMG-CoA synthase
  2. Mevalonate kinase
  3. Acetyl-CoA carboxylase
  4. HMG-CoA reductase Correct answer.

Explanation

HMG-CoA reductase converts HMG-CoA to mevalonate and is the rate-limiting, committed step of cholesterol synthesis; it is the target of statins. Acetyl-CoA carboxylase governs fatty acid synthesis instead.

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

A child presents with fasting hypoglycemia, hepatomegaly, and lactic acidosis, and liver biopsy shows increased glycogen with normal branching. Which enzyme deficiency is most likely?

  1. Branching enzyme
  2. Muscle phosphorylase
  3. Glucose-6-phosphatase Correct answer.
  4. Acid alpha-glucosidase

Explanation

Glucose-6-phosphatase deficiency (von Gierke disease) prevents hepatic release of glucose, causing fasting hypoglycemia, hepatomegaly, and lactic acidosis with structurally normal glycogen. Branching enzyme deficiency produces abnormally branched glycogen, and muscle phosphorylase deficiency causes exercise intolerance without hypoglycemia.

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

Which amino acid is the precursor for serotonin biosynthesis?

  1. Histidine
  2. Glutamate
  3. Tyrosine
  4. Tryptophan Correct answer.

Explanation

Tryptophan is hydroxylated and then decarboxylated to form serotonin (5-hydroxytryptamine). Tyrosine is the precursor of catecholamines and melanin, while histidine gives rise to histamine.

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

A competitive inhibitor of an enzyme is added to an assay. Which change in kinetics is expected?

  1. Decreased Km with unchanged Vmax
  2. Increased apparent Km with unchanged Vmax Correct answer.
  3. Increased Vmax with unchanged Km
  4. Decreased Vmax with unchanged Km

Explanation

A competitive inhibitor binds the free enzyme and can be overcome by more substrate, so the apparent Km rises while Vmax remains unchanged. Noncompetitive inhibitors instead lower Vmax with Km unaffected.

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

In the malate-aspartate shuttle, which cytosolic substrate is reduced to carry reducing equivalents into the mitochondrion?

  1. Pyruvate
  2. Alpha-ketoglutarate
  3. Fumarate
  4. Oxaloacetate Correct answer.

Explanation

Cytosolic NADH reduces oxaloacetate to malate, which enters the mitochondrion and is reoxidized to regenerate NADH for oxidative phosphorylation. This shuttle is important in heart and liver, where it preserves the full ATP yield of glycolysis.

Question 41Pathology

Which blood cell is the primary effector of acute inflammation in the first hours after tissue injury?

  1. Neutrophil Correct answer.
  2. Plasma cell
  3. Fibroblast
  4. Eosinophil

Explanation

Acute inflammation is characterized by neutrophil-predominant infiltrates that arrive within minutes to hours after injury. Neutrophils phagocytose organisms and debris and then typically undergo apoptosis within days.

Question 42Pathology

A 60-year-old man has a firm, painless nodule in the liver with abundant collagen and spindle cells on biopsy. Which process does this lesion most directly represent?

  1. Fibrosis with scar formation Correct answer.
  2. Coagulative necrosis
  3. Caseous necrosis
  4. Apoptosis of hepatocytes

Explanation

Deposition of collagen by fibroblasts with spindle cell proliferation is the histologic signature of fibrosis and scarring. This follows chronic injury and represents repair rather than a form of cell death.

Question 43Pathology

Which type of necrosis is classically seen in the brain after an ischemic infarct?

  1. Fat necrosis
  2. Liquefactive necrosis Correct answer.
  3. Fibrinoid necrosis
  4. Caseous necrosis

Explanation

Infarcted brain tissue undergoes enzymatic digestion resulting in liquefactive necrosis and cystic cavitation. The central nervous system lacks the structural rigidity that preserves architecture in coagulative necrosis elsewhere.

Question 44Pathology

A patient with a chronic wound shows granulation tissue on biopsy. Which feature is expected?

  1. Dense acellular collagen only
  2. Proliferating capillaries with fibroblasts and inflammatory cells Correct answer.
  3. Sheets of atypical keratinocytes
  4. Extensive caseous debris

Explanation

Granulation tissue is composed of proliferating small blood vessels, fibroblasts, and a mixed inflammatory infiltrate. It appears as red, granular tissue at the base of healing wounds.

Question 45Pathology

Which immunoglobulin is the main antibody produced in primary immune responses before class switching?

  1. IgG
  2. IgE
  3. IgM Correct answer.
  4. IgA

Explanation

Naive B cells express surface IgM, and the initial antibody response is predominantly IgM. Class switching to IgG, IgA, or IgE occurs later with T-cell help.

Question 46Pathology

Which cells present antigen via MHC class II molecules to CD4 T lymphocytes?

  1. CD8 T cells
  2. Erythrocytes
  3. Dendritic cells Correct answer.
  4. Neutrophils

Explanation

Professional antigen-presenting cells such as dendritic cells, macrophages, and B cells express MHC class II and activate CD4 helper T cells. Dendritic cells are the most potent of these.

Question 47Pathology

A patient develops urticaria and hypotension minutes after a penicillin injection. Which mechanism underlies this reaction?

  1. Type IV T-cell-mediated hypersensitivity
  2. Type II antibody-mediated cytotoxicity
  3. Type III immune complex deposition
  4. Type I IgE-mediated mast cell degranulation Correct answer.

Explanation

Immediate anaphylaxis results from cross-linking of IgE on mast cells, causing degranulation and release of histamine and other mediators. This is the classic type I hypersensitivity mechanism.

Question 48Pathology

Which autoantibody is most characteristic of systemic lupus erythematosus?

  1. Anti-mitochondrial antibody
  2. Anti-glomerular basement membrane antibody
  3. Anti-double-stranded DNA Correct answer.
  4. Anti-centromere antibody

Explanation

Anti-double-stranded DNA antibodies are highly specific for systemic lupus erythematosus and correlate with disease activity and lupus nephritis.

Question 49Pathology

A 45-year-old woman has a firm, painless breast mass with stony-hard consistency and skin dimpling. Which pathologic process best explains the dimpling?

  1. Fat necrosis with calcification
  2. Fibroadenoma with capsule formation
  3. Invasive carcinoma with desmoplastic reaction and lymphatic obstruction Correct answer.
  4. Acute mastitis with abscess

Explanation

Invasive breast carcinoma induces a desmoplastic stromal response and obstructs dermal lymphatics, tethering the skin and producing dimpling. Fibroadenomas are well-circumscribed and mobile.

Question 50Pathology

Which tumor suppressor gene is most commonly inactivated in human cancers?

  1. VHL
  2. APC
  3. TP53 Correct answer.
  4. RB1

Explanation

TP53 is mutated or inactivated in more than half of human cancers, making it the most frequently altered tumor suppressor gene. Its product, p53, regulates cell cycle arrest and apoptosis in response to DNA damage.