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ADC Written Exam (Dental Hygiene) study materials
ADC Written Exam (Dental Hygiene) study resources

ADC Written Exam (Dental Hygiene) practice questions

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Question 1Biomedical sciences (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

Which dental hard tissue contains the greatest proportion of inorganic mineral by weight?

  1. Enamel Correct answer.
  2. Pulp
  3. Dentin
  4. Cementum

Explanation

Enamel is the most highly mineralized tissue in the body, composed of roughly 96% inorganic material by weight, chiefly carbonated hydroxyapatite. Dentin and cementum contain substantially more organic matrix and water, and pulp is a soft connective tissue.

Question 2Biomedical sciences (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

Which organism is regarded as the principal initiator of smooth-surface enamel caries?

  1. Candida albicans
  2. Porphyromonas gingivalis
  3. Veillonella parvula
  4. Streptococcus mutans Correct answer.

Explanation

Streptococcus mutans initiates enamel caries because it adheres to the acquired pellicle, produces glucans from sucrose via glucosyltransferase, and ferments carbohydrate to acid rapidly. These properties allow it to colonize and demineralize enamel under a low pH.

Question 3Biomedical sciences (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

The resting pH of whole saliva in a healthy adult is closest to which value?

  1. 7.0 Correct answer.
  2. 6.0
  3. 5.0
  4. 8.5

Explanation

Resting whole saliva is normally slightly acidic to neutral, with a pH of approximately 6.7 to 7.4, so 7.0 is the closest of the listed values. Salivary pH rises toward the neutral range as flow rate increases because of increased bicarbonate output.

Question 4Biomedical sciences (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

Deficiency of which vitamin impairs hydroxylation of proline and lysine during collagen synthesis?

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

Explanation

Vitamin C (ascorbate) is the cofactor for prolyl and lysyl hydroxylase, enzymes that stabilize the collagen triple helix. Without hydroxylation, collagen is unstable and connective tissues weaken, producing the gingival bleeding and poor wound healing seen in scurvy.

Question 5Biomedical sciences (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

How many teeth are present in a complete permanent dentition, including third molars?

  1. 32 Correct answer.
  2. 20
  3. 24
  4. 28

Explanation

A full permanent dentition contains 32 teeth, comprising eight per quadrant from central incisor through third molar. The count falls to 28 when third molars are absent or extracted.

Question 6Biomedical sciences (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

Which of the following local anesthetics belongs to the ester class?

  1. Articaine
  2. Mepivacaine
  3. Benzocaine Correct answer.
  4. Lidocaine

Explanation

Benzocaine is an ester-type local anesthetic and is metabolized by plasma pseudocholinesterases to para-aminobenzoic acid, a known allergen. Lidocaine, mepivacaine and articaine are all amide anesthetics metabolized mainly in the liver.

Question 7Biomedical sciences (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

Which buffer system provides the greatest buffering capacity in stimulated whole saliva?

  1. Phosphate
  2. Bicarbonate Correct answer.
  3. Protein and albumin
  4. Ammonia

Explanation

Bicarbonate is the dominant salivary buffer, and its concentration rises sharply with salivary flow, so it accounts for most buffering in stimulated saliva. The phosphate system contributes more in resting saliva but is quantitatively smaller overall.

Question 8Biomedical sciences (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

Recurrent herpes labialis is most commonly caused by which agent?

  1. Coxsackievirus A
  2. Herpes simplex virus type 1 Correct answer.
  3. Human papillomavirus type 6
  4. Varicella-zoster virus

Explanation

Herpes simplex virus type 1 establishes latency in the trigeminal ganglion and reactivates to produce recurrent vesicles on the vermilion border. Sunlight, stress and fever are common triggers of reactivation.

Question 9Biomedical sciences (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

Which muscle of mastication is primarily responsible for protruding the mandible?

  1. Lateral pterygoid Correct answer.
  2. Masseter
  3. Medial pterygoid
  4. Temporalis

Explanation

The inferior head of the lateral pterygoid pulls the condyle and disc forward, producing protrusion and contributing to opening. The other masticatory muscles are primarily elevators or retractors of the mandible.

Question 10Biomedical sciences (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

Increased secretion of parathyroid hormone produces which net effect?

  1. Decreased osteoclastic bone resorption
  2. Increased serum calcium concentration Correct answer.
  3. Increased renal phosphate reabsorption
  4. Decreased intestinal calcium absorption

Explanation

Parathyroid hormone raises serum calcium by increasing renal tubular calcium reabsorption, stimulating bone resorption, and promoting renal conversion of vitamin D to calcitriol, which increases intestinal calcium uptake. It simultaneously reduces renal phosphate reabsorption, producing phosphaturia.

Question 11Biomedical sciences (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

Fluoride reduces enamel demineralization chiefly through which mechanism?

  1. Conversion of hydroxyapatite to less soluble fluorapatite Correct answer.
  2. Raising salivary pH through bacterial urease activity
  3. Removal of calcium from plaque fluid
  4. Neutralization of plaque acid by salivary bicarbonate

Explanation

Fluoride substitutes for hydroxyl groups in the apatite lattice, forming fluorapatite, which has a lower solubility and a lower critical pH than hydroxyapatite. This makes the enamel surface more resistant to acid challenge and favors remineralization.

Question 12Biomedical sciences (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

Which event represents the earliest vascular change in acute inflammation?

  1. Vasodilation of arterioles Correct answer.
  2. Exudation of fibrin
  3. Proliferation of fibroblasts
  4. Margination of neutrophils

Explanation

Acute inflammation begins with transient vasoconstriction followed by vasodilation of arterioles and opening of capillary beds, which increases blood flow and produces the redness and heat of inflammation. Increased permeability and leukocyte margination occur after this flow change.

Question 13Biomedical sciences (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

Which microbial complex of subgingival plaque is most strongly associated with severe chronic periodontitis and deep periodontal pockets?

  1. Yellow complex
  2. Red complex Correct answer.
  3. Green complex
  4. Purple complex

Explanation

The red complex, comprising Porphyromonas gingivalis, Tannerella forsythia and Treponema denticola, shows the strongest association with advanced attachment loss and deep bleeding pockets. The other complexes are typically associated with health or early colonization.

Question 14Biomedical sciences (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

Adding epinephrine to a local anesthetic solution produces which principal effect?

  1. Increases the systemic toxicity of the anesthetic
  2. Raises the pH of the cartridge solution
  3. Prolongs duration by reducing local blood flow Correct answer.
  4. Shortens the latency of anesthesia

Explanation

Epinephrine constricts local vessels, slowing clearance of the anesthetic from the injection site, which prolongs the duration of anesthesia and reduces peak systemic absorption. Less systemic absorption also lowers the risk of anesthetic toxicity.

Question 15Biomedical sciences (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

Ibuprofen reduces postoperative dental pain primarily through which action?

  1. Inhibition of phospholipase C activity
  2. Activation of peripheral opioid receptors
  3. Inhibition of cyclooxygenase and prostaglandin synthesis Correct answer.
  4. Blockade of voltage-gated sodium channels in sensory neurons

Explanation

Ibuprofen is a nonselective nonsteroidal anti-inflammatory drug that inhibits cyclooxygenase-1 and cyclooxygenase-2, reducing prostaglandin synthesis at the site of injury. Lower prostaglandin levels reduce nociceptor sensitization and the inflammatory response.

Question 16Biomedical sciences (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

During the upstroke of a neuronal action potential, which ion movement predominates?

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

Explanation

Depolarization to threshold opens voltage-gated sodium channels, and rapid sodium influx drives the membrane potential toward the sodium equilibrium potential. Repolarization then results from sodium channel inactivation and potassium efflux.

Question 17Biomedical sciences (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

Taste sensation from the anterior two-thirds of the tongue is carried by which nerve?

  1. Chorda tympani (CN VII) Correct answer.
  2. Lingual nerve (CN V3)
  3. Glossopharyngeal nerve (CN IX)
  4. Hypoglossal nerve (CN XII)

Explanation

Taste fibers from the anterior two-thirds of the tongue travel with the chorda tympani, a branch of the facial nerve, before joining the lingual nerve. The lingual nerve supplies general sensation to the same region but not taste.

Question 18Biomedical sciences (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

Under aerobic conditions, which compound is the end product of glycolysis?

  1. Acetyl-CoA
  2. Glucose-6-phosphate
  3. Pyruvate Correct answer.
  4. Lactate

Explanation

Glycolysis converts one glucose into two molecules of pyruvate with net production of two ATP and two NADH. Pyruvate is then decarboxylated to acetyl-CoA for entry into the citric acid cycle when oxygen is available.

Question 19Biomedical sciences (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

Which cell type is the principal source of collagen in healing gingival connective tissue?

  1. Fibroblast Correct answer.
  2. Osteoclast
  3. Macrophage
  4. Endothelial cell

Explanation

Fibroblasts synthesize and secrete procollagen, which is processed extracellularly into mature collagen fibrils during connective tissue repair. They also produce ground substance and help reorganize the healed periodontal matrix.

Question 20Biomedical sciences (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

Vitamin K deficiency prolongs the prothrombin time because the vitamin is required for which process?

  1. Carboxylation of glutamate residues on clotting factors Correct answer.
  2. Heparin-mediated activation of antithrombin III by endothelium
  3. ADP-mediated platelet granule release
  4. Cross-linking of fibrin monomers by factor XIII

Explanation

Vitamin K is the cofactor for gamma-carboxylation of glutamate residues on factors II, VII, IX and X, as well as proteins C and S, allowing them to bind calcium and phospholipid surfaces. Without carboxylation these factors are functionally inactive, prolonging the prothrombin time.

Question 21Biomedical sciences (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

A patient with prolonged vomiting develops metabolic alkalosis. Which respiratory compensation is expected?

  1. Hyperventilation, lowering PaCO2
  2. Increased tidal volume with an unchanged rate
  3. Irregular breathing with a variable PaCO2
  4. Hypoventilation, raising PaCO2 Correct answer.

Explanation

In metabolic alkalosis the respiratory center is depressed by the rising pH, so ventilation decreases and carbon dioxide is retained. The resulting rise in PaCO2 shifts the carbonic acid ratio back toward normal, partially correcting the pH.

Question 22Biomedical sciences (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

Viridans streptococci are the leading cause of infective endocarditis after dental procedures because these organisms characteristically do which of the following?

  1. Produce proteases that degrade heart valve tissue
  2. Secrete endotoxin that lyses endothelium
  3. Are the only oral bacteria that survive in blood
  4. Adhere to damaged endocardium and form biofilm Correct answer.

Explanation

Viridans streptococci adhere to fibronectin and fibrin-platelet deposits on damaged endocardium, where dextran production promotes dense biofilm formation that shields them from host defenses. Transient bacteremia during dental manipulation seeds these adherent organisms onto susceptible valves.

Question 23Biomedical sciences (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

Tetracycline can cause permanent yellow-brown discoloration of teeth because the drug does which of the following?

  1. Binds covalently to salivary mucin glycoproteins
  2. Chelates calcium in developing enamel and dentin Correct answer.
  3. Inhibits ameloblast collagen synthesis directly
  4. Blocks carbonic anhydrase in odontoblasts

Explanation

Tetracyclines chelate calcium ions and are incorporated into hydroxyapatite during odontogenesis, producing intrinsic staining that darkens with light exposure. The risk is greatest when the drug is given during the period of tooth development.

Question 24Biomedical sciences (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

A patient stabilized on warfarin is prescribed metronidazole, and the INR rises sharply. Which mechanism explains this interaction?

  1. Inhibition of CYP2C9-mediated metabolism Correct answer.
  2. Induction of hepatic warfarin metabolism
  3. Increased gut synthesis of vitamin K
  4. Displacement of warfarin from plasma albumin

Explanation

Metronidazole inhibits cytochrome P450 2C9, the principal enzyme that clears S-warfarin, so warfarin accumulates and the INR rises. The interaction can produce clinically significant bleeding and requires dose adjustment or selection of an alternative antimicrobial.

Question 25Biomedical sciences (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

Delayed periodontal healing in a patient with poorly controlled diabetes mellitus is best explained by which underlying change?

  1. Defective neutrophil chemotaxis and collagen synthesis Correct answer.
  2. Excessive production of salivary antimicrobial proteins
  3. Enhanced platelet aggregation in gingival tissue
  4. Increased salivary flow rate and buffering

Explanation

Chronic hyperglycemia impairs neutrophil chemotaxis and phagocytosis while reducing fibroblast proliferation and collagen synthesis, so both host defense and repair are compromised. Microangiopathy further limits delivery of oxygen and nutrients to healing periodontal tissues.

Question 26Biomedical sciences (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

Which enzyme in saliva initiates the digestion of dietary starch?

  1. Pepsin
  2. Trypsin
  3. Lipase
  4. Salivary amylase Correct answer.

Explanation

Salivary amylase hydrolyzes alpha-1,4 glycosidic bonds within starch, producing maltose and shorter oligosaccharides. Chemical digestion of starch therefore begins in the mouth before the food is swallowed.

Question 27Biomedical sciences (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

What is the normal pH range of arterial blood?

  1. 7.55 to 7.65
  2. 6.80 to 7.00
  3. 7.35 to 7.45 Correct answer.
  4. 7.00 to 7.20

Explanation

Arterial blood pH is tightly regulated between approximately 7.35 and 7.45 by buffer systems, the respiratory system, and the kidneys. Values outside this narrow range represent acidemia or alkalemia.

Question 28Biomedical sciences (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

Which vitamin is synthesized in the skin after exposure to ultraviolet light?

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

Explanation

Ultraviolet B radiation converts 7-dehydrocholesterol in the epidermis into cholecalciferol, which is subsequently hydroxylated in the liver and kidney to active vitamin D. This pathway makes the skin a major source of vitamin D.

Question 29Biomedical sciences (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

Which immunoglobulin is the predominant antibody in saliva?

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

Explanation

Secretory IgA is produced by plasma cells near salivary glands and is transported across epithelium with a secretory component. It is the dominant immunoglobulin in saliva and other mucosal secretions.

Question 30Biomedical sciences (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

Which nerve supplies motor innervation to the muscles of mastication?

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

Explanation

The mandibular division of the trigeminal nerve supplies the masseter, temporalis, medial pterygoid, and lateral pterygoid muscles. These muscles elevate, depress, protrude, and retrude the mandible.

Question 31Biomedical sciences (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

Which blood cell type is primarily responsible for transporting oxygen from the lungs to tissues?

  1. Erythrocytes Correct answer.
  2. Neutrophils
  3. Lymphocytes
  4. Platelets

Explanation

Erythrocytes contain hemoglobin, which binds oxygen in the pulmonary capillaries and releases it in peripheral tissues. Their biconcave shape increases surface area and permits deformation through small vessels.

Question 32Biomedical sciences (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

Which ion is the principal extracellular cation?

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

Explanation

Sodium is the most abundant cation in extracellular fluid and largely determines plasma osmolality. Potassium, by contrast, is the principal intracellular cation.

Question 33Biomedical sciences (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

Which organism is a gram-negative, anaerobic, black-pigmenting bacterium strongly linked to chronic periodontitis?

  1. Streptococcus mutans
  2. Actinomyces israelii
  3. Porphyromonas gingivalis Correct answer.
  4. Aggregatibacter actinomycetemcomitans

Explanation

Porphyromonas gingivalis is a gram-negative anaerobic coccobacillus that forms black-pigmented colonies and is strongly associated with severe chronic periodontitis. It possesses multiple virulence factors, including gingipains, that promote tissue destruction and immune evasion.

Question 34Biomedical sciences (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

Which enzyme converts angiotensin I to angiotensin II?

  1. Renin
  2. Angiotensin-converting enzyme Correct answer.
  3. Carbonic anhydrase
  4. Aldosterone synthase

Explanation

Angiotensin-converting enzyme, located on the surface of pulmonary and renal endothelial cells, cleaves angiotensin I to the potent vasoconstrictor angiotensin II. Renin instead catalyzes the preceding step that generates angiotensin I.

Question 35Biomedical sciences (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

Ventricular filling of the heart occurs primarily during which phase of the cardiac cycle?

  1. Diastole Correct answer.
  2. Systole
  3. Ejection phase
  4. Isovolumetric contraction

Explanation

Ventricular filling takes place during diastole, when the atrioventricular valves are open and ventricular pressure is below atrial pressure. Most filling occurs passively, with a smaller contribution from atrial contraction.

Question 36Biomedical sciences (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

Which hormone raises blood glucose primarily by stimulating hepatic glycogenolysis?

  1. Insulin
  2. Glucagon Correct answer.
  3. Calcitonin
  4. Aldosterone

Explanation

Glucagon acts on hepatic cells to activate glycogen phosphorylase and promote glycogen breakdown, releasing glucose into the blood. It also stimulates gluconeogenesis, supporting blood glucose during fasting.

Question 37Biomedical sciences (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

Allergic contact dermatitis to a dental material is mediated by which type of hypersensitivity reaction?

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

Explanation

Allergic contact dermatitis is a delayed, cell-mediated hypersensitivity reaction in which sensitized T lymphocytes release cytokines after re-exposure to the allergen. It is classified as type IV hypersensitivity and typically develops 24 to 72 hours after contact.

Question 38Biomedical sciences (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

Which process describes programmed cell death as part of normal tissue turnover?

  1. Mitosis
  2. Metaplasia
  3. Necrosis
  4. Apoptosis Correct answer.

Explanation

Apoptosis is an energy-dependent, genetically controlled form of cell death that removes unwanted or damaged cells without provoking inflammation. It is essential for normal development and tissue homeostasis.

Question 39Biomedical sciences (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

Which complement fragment acts as the major opsonin for phagocytosis of bacteria?

  1. C3a
  2. C5a
  3. C3b Correct answer.
  4. C9

Explanation

C3b covalently binds to microbial surfaces and is recognized by complement receptors on phagocytes, promoting opsonization and engulfment. This is a principal mechanism by which complement enhances bacterial clearance.

Question 40Biomedical sciences (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

Which drug class suppresses gastric acid secretion by irreversibly inhibiting the H+/K+-ATPase pump?

  1. Prostaglandin analogs
  2. Proton pump inhibitors Correct answer.
  3. Antacids
  4. Histamine H2-receptor antagonists

Explanation

Proton pump inhibitors bind covalently to the parietal cell H+/K+-ATPase, blocking the final step of acid secretion. Because the inhibition is irreversible, acid suppression persists until new pumps are synthesized.

Question 41Biomedical sciences (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

Which antibiotic class kills bacteria by binding penicillin-binding proteins and blocking cell wall cross-linking?

  1. Beta-lactams Correct answer.
  2. Tetracyclines
  3. Macrolides
  4. Aminoglycosides

Explanation

Beta-lactams bind penicillin-binding proteins, which are transpeptidases responsible for cross-linking peptidoglycan. This interference with cell wall synthesis weakens the bacterial wall and leads to lysis, especially in actively dividing organisms.

Question 42Biomedical sciences (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

Which nerve provides general sensory innervation to the hard palate?

  1. Inferior alveolar nerve
  2. Lingual nerve
  3. Chorda tympani
  4. Greater palatine nerve Correct answer.

Explanation

The greater palatine nerve, a branch of the maxillary division of the trigeminal nerve, supplies general sensation to the mucosa of the hard palate and palatal gingiva. It travels through the greater palatine canal and foramen.

Question 43Biomedical sciences (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

What is the principal fuel source for resting skeletal muscle?

  1. Fatty acids Correct answer.
  2. Ketone bodies
  3. Lactate
  4. Dietary protein

Explanation

At rest, skeletal muscle derives most of its ATP from oxidative metabolism of fatty acids delivered by the circulation. Glucose and glycogen become more important during higher-intensity contraction.

Question 44Biomedical sciences (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

Deficiency of vitamin B12 produces which type of anemia?

  1. Megaloblastic anemia Correct answer.
  2. Aplastic anemia
  3. Iron-deficiency anemia
  4. Hemolytic anemia

Explanation

Vitamin B12 is required for DNA synthesis and normal nuclear maturation of erythrocyte precursors. Deficiency leads to impaired cell division in the bone marrow and enlarged, nucleated red cell precursors characteristic of megaloblastic anemia.

Question 45Biomedical sciences (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

Which major salivary gland produces the largest volume of serous saliva?

  1. Parotid Correct answer.
  2. Minor mucous glands
  3. Sublingual
  4. Submandibular

Explanation

The parotid gland is the largest salivary gland and secretes primarily serous saliva, contributing the greatest volume of stimulated salivary flow. Submandibular saliva is mixed, while sublingual saliva is predominantly mucinous.

Question 46Biomedical sciences (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

Which renal tubular segment is impermeable to water and dilutes the tubular fluid?

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

Explanation

The ascending limb of the loop of Henle actively reabsorbs sodium and chloride while remaining impermeable to water. Solute removal without water leaves the tubular fluid progressively more dilute.

Question 47Biomedical sciences (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

Phenylketonuria results from deficiency of which enzyme?

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

Explanation

Phenylalanine hydroxylase converts phenylalanine to tyrosine, and its deficiency causes phenylalanine accumulation with alternative metabolite formation. If untreated, the excess phenylalanine impairs brain development and produces intellectual disability.

Question 48Biomedical sciences (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

Recurrent infections with Neisseria species are most strongly associated with deficiency of which complement component?

  1. C3
  2. C5 through C9 Correct answer.
  3. C4
  4. C1 inhibitor

Explanation

The terminal complement components C5 through C9 assemble into the membrane attack complex, which lyses gram-negative organisms such as Neisseria. Deficiency of these components permits recurrent disseminated gonococcal and meningococcal infections.

Question 49Biomedical sciences (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

Which cell type is predominantly responsible for wound contraction during the remodeling phase?

  1. Fibroblasts
  2. Myofibroblasts Correct answer.
  3. Endothelial cells
  4. Neutrophils

Explanation

Myofibroblasts are differentiated fibroblasts that contain smooth muscle actin and generate contractile forces to reduce wound size. Their activity characterizes the later proliferative and remodeling phases of healing.

Question 50Biomedical sciences (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

Which anticoagulant acts by directly inhibiting thrombin?

  1. Aspirin
  2. Warfarin
  3. Dabigatran Correct answer.
  4. Heparin

Explanation

Dabigatran is a direct oral thrombin inhibitor that binds free and clot-bound thrombin, preventing fibrin formation. Warfarin reduces synthesis of vitamin K-dependent clotting factors, while heparin enhances antithrombin activity.