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NOTCE practice questions

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Question 1Basic and Clinical Sciences

Which cranial nerve carries parasympathetic fibers to the parotid gland?

  1. Glossopharyngeal nerve (CN IX) Correct answer.
  2. Hypoglossal nerve (CN XII)
  3. Trigeminal nerve (CN V)
  4. Facial nerve (CN VII)

Explanation

Parasympathetic secretomotor fibers to the parotid gland travel with the glossopharyngeal nerve, synapsing in the otic ganglion before reaching the gland via the auriculotemporal nerve. The facial nerve supplies the other major salivary glands instead.

Question 2Basic and Clinical Sciences

During the cardiac cycle, which event immediately follows closure of the aortic and pulmonary valves?

  1. Atrial systole
  2. Isovolumetric ventricular contraction
  3. Rapid ventricular ejection
  4. Isovolumetric ventricular relaxation Correct answer.

Explanation

Closure of the semilunar valves marks the start of the second heart sound and the beginning of isovolumetric relaxation, when ventricular pressure falls while all valves remain closed. Atrial systole and ejection occur at other phases of the cycle.

Question 3Basic and Clinical Sciences

A patient has a lesion of the upper trunk of the brachial plexus. Which movement is most likely impaired?

  1. Wrist extension
  2. Finger abduction
  3. Thumb opposition
  4. Shoulder abduction and elbow flexion Correct answer.

Explanation

The upper trunk gives rise to the musculocutaneous and axillary nerves, so lesions impair elbow flexion and shoulder abduction. Finger abduction depends on the lower trunk via the ulnar nerve.

Question 4Basic and Clinical Sciences

Which hormone is released from the posterior pituitary?

  1. Prolactin
  2. Growth hormone
  3. Oxytocin Correct answer.
  4. Adrenocorticotropic hormone

Explanation

The posterior pituitary stores and releases oxytocin and vasopressin, which are synthesized in the hypothalamus. Prolactin, ACTH, and growth hormone are anterior pituitary hormones.

Question 5Basic and Clinical Sciences

Which immunoglobulin class is the first to be produced in a primary humoral immune response?

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

Explanation

IgM is the earliest antibody class produced in a primary response and is a potent activator of complement. IgG dominates later secondary responses, while IgA and IgE serve mucosal and allergic roles.

Question 6Basic and Clinical Sciences

A deficiency of vitamin B12 leads to which hematologic finding?

  1. Microcytic hypochromic anemia
  2. Normocytic anemia with schistocytes
  3. Isolated thrombocytosis
  4. Macrocytic anemia with hypersegmented neutrophils Correct answer.

Explanation

Vitamin B12 deficiency impairs DNA synthesis, producing megaloblastic changes such as macrocytic anemia and hypersegmented neutrophils. Iron deficiency instead causes microcytic hypochromic anemia.

Question 7Basic and Clinical Sciences

Which enzyme catalyzes the rate-limiting step of glycolysis?

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

Explanation

Phosphofructokinase-1 catalyzes the committed, rate-limiting step converting fructose-6-phosphate to fructose-1,6-bisphosphate. It is regulated by ATP, citrate, and AMP.

Question 8Basic and Clinical Sciences

Which structure separates the left and right ventricles of the heart?

  1. Atrioventricular septum
  2. Interatrial septum
  3. Interventricular septum Correct answer.
  4. Fibrous pericardium

Explanation

The interventricular septum is the muscular and membranous wall dividing the two ventricles. The interatrial septum separates the atria instead.

Question 9Basic and Clinical Sciences

A patient with a lesion of the dorsal columns of the spinal cord will most likely have impaired:

  1. Voluntary bladder control
  2. Vibration and proprioception Correct answer.
  3. Motor strength in the limbs
  4. Pain and temperature sensation

Explanation

The dorsal columns carry fine touch, vibration, and conscious proprioception via the medial lemniscus pathway. Pain and temperature travel in the spinothalamic tract.

Question 10Basic and Clinical Sciences

Which acid-base disturbance is expected in a patient with prolonged vomiting?

  1. Metabolic acidosis
  2. Respiratory acidosis
  3. Respiratory alkalosis
  4. Metabolic alkalosis Correct answer.

Explanation

Vomiting causes loss of hydrogen ions and chloride, generating a hypochloremic metabolic alkalosis. Respiratory compensation is hypoventilation, which raises PaCO2.

Question 11Basic and Clinical Sciences

Which drug mechanism characterizes beta-lactam antibiotics?

  1. Disruption of fungal cell membranes
  2. Inhibition of DNA gyrase
  3. Inhibition of bacterial cell wall cross-linking Correct answer.
  4. Inhibition of bacterial protein synthesis at the 30S subunit

Explanation

Beta-lactams bind penicillin-binding proteins and block peptidoglycan cross-linking in the bacterial cell wall. Protein synthesis inhibitors and fluoroquinolones act by other mechanisms.

Question 12Basic and Clinical Sciences

A patient presents with loss of pain and temperature sensation on the left side of the face and the right side of the body. Where is the lesion most likely located?

  1. Right spinal cord at C5
  2. Right lateral medulla
  3. Left lateral medulla Correct answer.
  4. Left internal capsule

Explanation

This pattern indicates Wallenberg syndrome: a left lateral medullary lesion damages the left spinal trigeminal nucleus (ipsilateral facial pain/temperature loss) and the left spinothalamic tract (contralateral body pain/temperature loss).

Question 13Basic and Clinical Sciences

Which renal structure is primarily responsible for creating the medullary osmotic gradient?

  1. Loop of Henle Correct answer.
  2. Macula densa
  3. Bowman capsule
  4. Glomerulus

Explanation

The thick ascending limb of the loop of Henle actively reabsorbs sodium chloride while remaining impermeable to water, generating the countercurrent multiplier that establishes the medullary osmotic gradient. The other structures are involved in filtration or signaling.

Question 14Basic and Clinical Sciences

Which phase of the cell cycle is the primary target of vinca alkaloids?

  1. S phase
  2. G1 phase
  3. G0 phase
  4. M phase Correct answer.

Explanation

Vinca alkaloids inhibit microtubule polymerization, arresting cells in metaphase of mitosis, so they are M-phase specific. Antimetabolites such as methotrexate act in S phase.

Question 15Basic and Clinical Sciences

A patient with severe diarrhea develops a serum potassium of 2.9 mmol/L. Which mechanism best explains the hypokalemia?

  1. Cellular potassium shift into bone
  2. Decreased potassium intake
  3. Reduced aldosterone secretion
  4. Increased renal potassium excretion due to aldosterone and distal flow Correct answer.

Explanation

Diarrhea causes volume depletion, activating the renin-angiotensin-aldosterone system; aldosterone plus increased distal tubular flow promotes potassium excretion, causing hypokalemia. Reduced aldosterone would instead cause hyperkalemia.

Question 16Basic and Clinical Sciences

Which type of hypersensitivity reaction underlies acute hemolytic transfusion reactions?

  1. Type III hypersensitivity
  2. Type IV hypersensitivity
  3. Type I hypersensitivity
  4. Type II hypersensitivity Correct answer.

Explanation

Acute hemolytic transfusion reactions are type II hypersensitivity reactions in which preformed antibodies bind donor red cell antigens, activating complement and causing intravascular hemolysis.

Question 17Basic and Clinical Sciences

Which cranial nerve is tested by asking the patient to shrug the shoulders against resistance?

  1. Optic nerve (CN II)
  2. Facial nerve (CN VII)
  3. Accessory nerve (CN XI) Correct answer.
  4. Vagus nerve (CN X)

Explanation

The accessory nerve supplies the trapezius and sternocleidomastoid muscles, so shoulder shrug tests CN XI. The facial, vagus, and optic nerves serve other functions.

Question 18Basic and Clinical Sciences

Which lung volume cannot be measured by simple spirometry?

  1. Tidal volume
  2. Inspiratory reserve volume
  3. Expiratory reserve volume
  4. Residual volume Correct answer.

Explanation

Residual volume remains in the lungs after maximal expiration and cannot be exhaled into a spirometer, so it is measured by helium dilution or body plethysmography. The other volumes are directly measurable.

Question 19Basic and Clinical Sciences

Which metabolic pathway is the primary source of NADPH for reductive biosynthesis and glutathione regeneration?

  1. Glycolysis
  2. Pentose phosphate pathway Correct answer.
  3. Urea cycle
  4. Beta-oxidation

Explanation

The pentose phosphate pathway generates NADPH through glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase, supporting fatty acid synthesis and glutathione reduction. Glycolysis and beta-oxidation produce ATP, and the urea cycle handles nitrogen disposal.

Question 20Basic and Clinical Sciences

A patient taking warfarin is started on rifampin. What is the expected effect on anticoagulation?

  1. Enhanced effect due to displacement from albumin only
  2. No change because rifampin does not affect CYP enzymes
  3. Reduced warfarin effect due to enzyme induction Correct answer.
  4. Enhanced warfarin effect due to enzyme inhibition

Explanation

Rifampin is a potent inducer of hepatic cytochrome P450 enzymes, accelerating warfarin metabolism and reducing its anticoagulant effect. This can lead to subtherapeutic INR and thrombotic risk.

Question 21Basic and Clinical Sciences

Which fetal circulation shunt directs blood from the pulmonary artery to the aorta?

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

Explanation

The ductus arteriosus connects the pulmonary artery to the descending aorta, bypassing the fetal lungs. The foramen ovale shunts blood between the atria.

Question 22Basic and Clinical Sciences

Which neurotransmitter is deficient in the nigrostriatal pathway in Parkinson disease?

  1. GABA
  2. Acetylcholine
  3. Dopamine Correct answer.
  4. Serotonin

Explanation

Degeneration of dopaminergic neurons in the substantia nigra pars compacta reduces dopamine in the striatum, producing the motor features of Parkinson disease. Acetylcholine and GABA are not the primary deficient transmitters in this pathway.

Question 23Basic and Clinical Sciences

A newborn has cyanosis that does not improve with supplemental oxygen. Which congenital lesion is most consistent with this finding?

  1. Ventricular septal defect
  2. Atrial septal defect
  3. Transposition of the great arteries Correct answer.
  4. Patent ductus arteriosus

Explanation

Transposition of the great arteries creates parallel circulations with poorly oxygenated blood returning to the systemic circulation, so cyanosis persists despite oxygen therapy. Left-to-right shunts such as VSD, PDA, and ASD typically do not cause refractory cyanosis.

Question 24Basic and Clinical Sciences

Which cells are the primary source of insulin in the pancreas?

  1. Alpha cells of the islets of Langerhans
  2. Delta cells of the islets of Langerhans
  3. Beta cells of the islets of Langerhans Correct answer.
  4. Acinar cells

Explanation

Pancreatic beta cells synthesize and secrete insulin in response to rising blood glucose. Alpha cells secrete glucagon and delta cells secrete somatostatin.

Question 25Basic and Clinical Sciences

A patient has metabolic acidosis with a high anion gap. Which condition best fits this pattern?

  1. Primary hyperaldosteronism
  2. Prolonged vomiting
  3. Excessive antacid ingestion
  4. Diabetic ketoacidosis Correct answer.

Explanation

Diabetic ketoacidosis accumulates ketoacids, raising the anion gap and producing metabolic acidosis. Vomiting and hyperaldosteronism instead cause metabolic alkalosis.

Question 26Basic and Clinical Sciences

A patient with a history of recurrent kidney stones has a serum calcium of 11.2 mg/dL and a serum phosphate of 2.0 mg/dL. Which additional finding is most characteristic of primary hyperparathyroidism?

  1. Elevated serum calcitonin level
  2. Low serum alkaline phosphatase level
  3. Low serum parathyroid hormone (PTH) level
  4. Elevated serum parathyroid hormone (PTH) level Correct answer.

Explanation

Primary hyperparathyroidism is characterized by hypercalcemia, hypophosphatemia, and an elevated or inappropriately normal PTH level. The high PTH drives bone resorption and renal calcium reabsorption, causing the observed electrolyte pattern. Calcitonin is typically normal or low, and alkaline phosphatase may be elevated due to increased bone turnover.

Question 27Basic and Clinical Sciences

Which component of the cardiac conduction system normally exhibits the slowest conduction velocity, thereby allowing time for ventricular filling?

  1. Bundle of His
  2. Atrioventricular (AV) node Correct answer.
  3. Sinoatrial (SA) node
  4. Purkinje fibers

Explanation

The AV node has the slowest conduction velocity in the cardiac conduction system, creating a delay between atrial and ventricular depolarization. This delay ensures that the ventricles have time to fill before they contract. Purkinje fibers and the bundle of His conduct rapidly, while the SA node sets the pacemaker rate but does not provide the slowest conduction.

Question 28Basic and Clinical Sciences

A 45-year-old man with chronic alcohol use disorder presents with confusion and ataxia. MRI shows atrophy of the mammillary bodies. Which vitamin deficiency is most likely responsible?

  1. Vitamin B12
  2. Vitamin C
  3. Thiamine (vitamin B1) Correct answer.
  4. Niacin (vitamin B3)

Explanation

Thiamine deficiency, common in chronic alcohol use, causes Wernicke encephalopathy, which is characterized by confusion, ataxia, and ophthalmoplegia. Mammillary body atrophy is a hallmark finding. Prompt thiamine replacement is essential to prevent progression to Korsakoff syndrome.

Question 29Basic and Clinical Sciences

During a normal menstrual cycle, which hormonal change is primarily responsible for the mid-cycle surge in luteinizing hormone (LH)?

  1. Rising inhibin levels from the corpus luteum
  2. Positive feedback of high estrogen levels on the hypothalamus and anterior pituitary Correct answer.
  3. Direct stimulation of the ovary by follicle-stimulating hormone (FSH)
  4. Negative feedback of progesterone on the hypothalamus

Explanation

Late in the follicular phase, estrogen levels rise and exert positive feedback on the hypothalamus and anterior pituitary, triggering the LH surge that induces ovulation. This is a classic example of positive feedback in endocrine physiology. Progesterone and inhibin generally exert negative feedback.

Question 30Basic and Clinical Sciences

A patient is prescribed a drug that inhibits the enzyme cyclooxygenase (COX). Which downstream effect is most directly reduced by this mechanism?

  1. Release of histamine from mast cells
  2. Production of leukotrienes from arachidonic acid
  3. Synthesis of prostaglandins from arachidonic acid Correct answer.
  4. Activation of the complement cascade

Explanation

Cyclooxygenase catalyzes the conversion of arachidonic acid to prostaglandin H2, the precursor of prostaglandins and thromboxanes. Inhibiting COX reduces prostaglandin synthesis, which accounts for the anti-inflammatory, analgesic, and antipyretic effects of NSAIDs. Leukotrienes are produced via the lipoxygenase pathway and are not directly affected.

Question 31Basic and Clinical Sciences

A 62-year-old woman with a history of breast cancer presents with confusion and a serum calcium of 13.5 mg/dL. Which mechanism most likely explains the hypercalcemia?

  1. Parathyroid hormone-related peptide (PTHrP) secretion by the tumor Correct answer.
  2. Thiazide diuretic use
  3. Vitamin D intoxication
  4. Primary hyperparathyroidism

Explanation

Humoral hypercalcemia of malignancy is often mediated by PTHrP secreted by solid tumors such as breast cancer. PTHrP binds PTH receptors, increasing bone resorption and renal calcium reabsorption. This is a common paraneoplastic syndrome and should be considered in cancer patients with hypercalcemia.

Question 32Basic and Clinical Sciences

Which renal tubular segment is the primary site of action of loop diuretics such as furosemide?

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

Explanation

Loop diuretics inhibit the Na+-K+-2Cl- cotransporter in the thick ascending limb of the loop of Henle, reducing the medullary osmotic gradient and producing potent diuresis. This segment is responsible for creating the hypertonic medullary interstitium. Other diuretics act at different tubular sites.

Question 33Basic and Clinical Sciences

A patient with a history of peptic ulcer disease is found to have a gastric pH of 1.5. Which cell type is primarily responsible for secreting hydrochloric acid in the stomach?

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

Explanation

Parietal cells in the gastric glands secrete hydrochloric acid via the H+/K+-ATPase proton pump. They are stimulated by histamine, gastrin, and acetylcholine. Chief cells secrete pepsinogen, G cells secrete gastrin, and mucous neck cells secrete mucus.

Question 34Basic and Clinical Sciences

A 70-year-old man presents with sudden onset of severe abdominal pain and is found to have an abdominal aortic aneurysm that has ruptured. Which underlying process most directly weakens the aortic wall in this condition?

  1. Proliferation of smooth muscle cells in the media
  2. Accumulation of lipid-laden macrophages in the adventitia
  3. Deposition of calcium in the intima
  4. Degradation of elastin and collagen by matrix metalloproteinases Correct answer.

Explanation

Abdominal aortic aneurysms are characterized by degradation of extracellular matrix proteins, particularly elastin and collagen, by matrix metalloproteinases. This weakening of the tunica media leads to dilation and risk of rupture. Atherosclerosis and inflammation contribute to this process.

Question 35Basic and Clinical Sciences

A patient is started on a drug that inhibits the enzyme dihydrofolate reductase (DHFR). Which metabolite is most directly depleted by this inhibition?

  1. S-adenosylmethionine (SAM)
  2. Tetrahydrofolate (THF) Correct answer.
  3. Homocysteine
  4. Methylmalonyl-CoA

Explanation

Dihydrofolate reductase converts dihydrofolate to tetrahydrofolate, which is essential for thymidylate and purine synthesis. Inhibitors such as methotrexate deplete THF, impairing DNA synthesis. SAM, homocysteine, and methylmalonyl-CoA are not directly depleted by DHFR inhibition.

Question 36Basic and Clinical Sciences

Which type of sensory receptor is primarily responsible for detecting fine touch and vibration?

  1. Ruffini endings
  2. Pacinian corpuscles
  3. Meissner corpuscles Correct answer.
  4. Free nerve endings

Explanation

Meissner corpuscles are rapidly adapting mechanoreceptors located in the dermal papillae that detect fine touch and low-frequency vibration. Pacinian corpuscles detect high-frequency vibration and deep pressure. Free nerve endings detect pain and temperature, and Ruffini endings detect stretch.

Question 37Basic and Clinical Sciences

A patient with a mutation in the gene encoding the beta-globin chain has hemoglobin that polymerizes when deoxygenated. Which hemoglobinopathy is most likely?

  1. Methemoglobinemia
  2. Hemoglobin H disease
  3. Beta-thalassemia major
  4. Sickle cell anemia Correct answer.

Explanation

Sickle cell anemia is caused by a point mutation in the beta-globin gene (HbS), which leads to polymerization of deoxygenated hemoglobin and sickling of red blood cells. This results in vaso-occlusive crises and hemolytic anemia. Beta-thalassemia involves reduced synthesis of beta-globin chains, not polymerization.

Question 38Basic and Clinical Sciences

A 55-year-old man with a history of chronic obstructive pulmonary disease (COPD) has an arterial blood gas showing pH 7.34, PaCO2 60 mmHg, and HCO3- 31 mEq/L. Which acid-base disturbance is most likely?

  1. Metabolic alkalosis with respiratory compensation
  2. Acute respiratory acidosis without compensation
  3. Mixed respiratory and metabolic acidosis
  4. Chronic respiratory acidosis with metabolic compensation Correct answer.

Explanation

The elevated PaCO2 indicates respiratory acidosis, and the elevated bicarbonate indicates metabolic compensation, which is typical of chronic respiratory acidosis. In acute respiratory acidosis, bicarbonate would be only minimally elevated. The near-normal pH suggests a chronic, compensated state.

Question 39Basic and Clinical Sciences

Which brain structure is the primary relay station for sensory pathways traveling to the cerebral cortex, with the exception of olfaction?

  1. Thalamus Correct answer.
  2. Cerebellum
  3. Basal ganglia
  4. Hypothalamus

Explanation

The thalamus serves as the major relay station for sensory information (except olfaction) ascending to the cerebral cortex. Each sensory modality (except smell) synapses in a specific thalamic nucleus before projecting to the cortex. The hypothalamus regulates homeostasis, the basal ganglia modulate movement, and the cerebellum coordinates motor activity.

Question 40Basic and Clinical Sciences

A patient is administered a drug that blocks voltage-gated sodium channels in their inactivated state. Which effect on the cardiac action potential is most likely?

  1. Prolonged phase 3 repolarization
  2. Increased phase 4 spontaneous depolarization
  3. Decreased phase 0 depolarization slope and slowed conduction Correct answer.
  4. Shortened phase 2 plateau

Explanation

Voltage-gated sodium channel blockers (class I antiarrhythmics) reduce the rapid influx of sodium during phase 0, decreasing the slope of depolarization and slowing conduction velocity. This can terminate reentrant arrhythmias. They do not primarily affect phase 3 repolarization or phase 4 depolarization.

Question 41Basic and Clinical Sciences

A patient with a history of recurrent infections is found to have a defect in the oxidative burst of neutrophils. Which enzyme is most likely deficient?

  1. NADPH oxidase Correct answer.
  2. Superoxide dismutase
  3. Catalase
  4. Myeloperoxidase

Explanation

Chronic granulomatous disease is caused by a defect in NADPH oxidase, which is responsible for the respiratory burst that generates superoxide radicals to kill phagocytosed bacteria. This leads to recurrent infections with catalase-positive organisms. Myeloperoxidase deficiency is usually asymptomatic, and superoxide dismutase and catalase are antioxidant enzymes.

Question 42Basic and Clinical Sciences

Which hormone is primarily responsible for the milk ejection reflex during breastfeeding?

  1. Progesterone
  2. Oxytocin Correct answer.
  3. Prolactin
  4. Estrogen

Explanation

Oxytocin, released from the posterior pituitary, causes contraction of myoepithelial cells around mammary alveoli, leading to milk ejection. Prolactin stimulates milk production, while estrogen and progesterone support breast development during pregnancy but do not mediate the ejection reflex.

Question 43Basic and Clinical Sciences

A 30-year-old woman presents with heat intolerance, weight loss, and a diffuse goiter. Laboratory tests show elevated T4 and suppressed TSH. Which autoantibody is most likely present?

  1. Anti-thyroid peroxidase (anti-TPO) antibody
  2. Thyroid-stimulating immunoglobulin (TSI) Correct answer.
  3. Anti-intrinsic factor antibody
  4. Anti-thyroglobulin antibody

Explanation

Graves disease is caused by thyroid-stimulating immunoglobulin (TSI), which binds to and activates the TSH receptor, leading to hyperthyroidism and diffuse goiter. Anti-TPO and anti-thyroglobulin antibodies are more characteristic of Hashimoto thyroiditis. Anti-intrinsic factor antibodies are seen in pernicious anemia.

Question 44Basic and Clinical Sciences

Which phase of the cell cycle is characterized by DNA replication?

  1. G2 phase
  2. S phase Correct answer.
  3. M phase
  4. G1 phase

Explanation

DNA replication occurs during the S (synthesis) phase of the cell cycle. G1 is the gap phase before replication, G2 is the gap phase after replication, and M phase is mitosis. Understanding these phases is important for chemotherapy targeting.

Question 45Basic and Clinical Sciences

A patient with severe liver disease has decreased albumin synthesis. Which consequence is most directly related to this decrease?

  1. Increased clotting factor synthesis
  2. Enhanced immune response
  3. Increased plasma oncotic pressure leading to dehydration
  4. Reduced plasma oncotic pressure leading to edema Correct answer.

Explanation

Albumin is the major contributor to plasma oncotic pressure, which draws fluid into the vascular space. Decreased albumin synthesis in liver disease reduces oncotic pressure, causing fluid to leak into interstitial spaces and produce edema. Clotting factors are also synthesized in the liver, so their production would be decreased, not increased.

Question 46Basic and Clinical Sciences

Which type of muscle tissue is characterized by involuntary contraction and is found in the walls of blood vessels?

  1. Striated muscle
  2. Skeletal muscle
  3. Cardiac muscle
  4. Smooth muscle Correct answer.

Explanation

Smooth muscle is involuntary and non-striated, and it is found in the walls of blood vessels, the gastrointestinal tract, and other viscera. Skeletal muscle is voluntary and striated, while cardiac muscle is involuntary but striated and found only in the heart.

Question 47Basic and Clinical Sciences

A 65-year-old man with a history of smoking presents with hemoptysis and a central lung mass. Biopsy shows small cells with neuroendocrine features. Which paraneoplastic syndrome is most commonly associated with this tumor?

  1. Hypercalcemia due to PTHrP
  2. Syndrome of inappropriate antidiuretic hormone (SIADH) Correct answer.
  3. Cushing syndrome due to ectopic ACTH
  4. Lambert-Eaton syndrome

Explanation

Small cell lung carcinoma is a neuroendocrine tumor that frequently causes paraneoplastic syndromes, most commonly SIADH, leading to hyponatremia. It can also cause ectopic ACTH and Lambert-Eaton syndrome, but SIADH is the most common. Hypercalcemia due to PTHrP is more typical of squamous cell carcinoma.

Question 48Basic and Clinical Sciences

Which mechanism best explains the diuresis observed after administration of mannitol?

  1. Inhibition of carbonic anhydrase
  2. Antagonism of aldosterone receptors
  3. Inhibition of the Na+-K+-2Cl- cotransporter
  4. Osmotic retention of water in the renal tubule Correct answer.

Explanation

Mannitol is an osmotic diuretic that is freely filtered but not reabsorbed, retaining water in the tubular lumen and increasing urine output. It does not inhibit specific transporters or receptors. Loop diuretics inhibit the Na+-K+-2Cl- cotransporter, and spironolactone antagonizes aldosterone.

Question 49Basic and Clinical Sciences

A patient with a deficiency of vitamin K is likely to have impaired function of which clotting factors?

  1. Factors V and VIII
  2. Factors XI and XII
  3. Factors VIII and IX
  4. Factors II, VII, IX, and X Correct answer.

Explanation

Vitamin K is a cofactor for the gamma-carboxylation of glutamate residues in clotting factors II, VII, IX, and X, as well as proteins C and S. Deficiency leads to prolonged prothrombin time and bleeding. Factors VIII and V are not vitamin K-dependent.

Question 50Basic and Clinical Sciences

A 50-year-old woman presents with fatigue, weight gain, and cold intolerance. Laboratory tests show elevated TSH and low free T4. Which finding is most consistent with this condition?

  1. Elevated anti-thyroid peroxidase antibodies Correct answer.
  2. Suppressed TSH
  3. Low serum cholesterol
  4. Elevated thyroid-stimulating immunoglobulin

Explanation

The presentation is consistent with primary hypothyroidism, most commonly due to Hashimoto thyroiditis, which is characterized by elevated anti-thyroid peroxidase antibodies. TSH is elevated due to loss of negative feedback. Thyroid-stimulating immunoglobulin is seen in Graves disease, and hypothyroidism is typically associated with hypercholesterolemia.