🧬 Cell & Tissue Architecture
A histology specimen shows epithelial cells attached to an underlying basal lamina. Which structure is primarily responsible for anchoring the epithelial cell to the basal lamina?
Hemidesmosomes
A newborn develops a scalp swelling following a difficult delivery. The swelling is located between the skin and galea and crosses cranial sutures. Which diagnosis is most likely?
A. Cephalohematoma
B. Caput succedaneum
C. Subgaleal hemorrhage
D. Epidural hematoma
E. Subdural hematoma
B. Caput succedaneum
A histologic section demonstrates cartilage containing thick bundles of type I collagen arranged between rows of chondrocytes. Which type of cartilage is present?
A. Hyaline
B. Elastic
C. Fibrocartilage
D. Reticular
E. Dense regular connective tissue
C. Fibrocartilage
A muscle biopsy demonstrates long cylindrical cells with prominent striations and multiple nuclei located at the periphery of the cell. Which tissue is being examined?
A. Cardiac muscle
B. Smooth muscle
C. Skeletal muscle
D. Dense connective tissue
E. Myoepithelium
C. Skeletal muscle
A newborn has a neural tube defect caused by failure of closure of the cranial neuropore. Which condition is most likely?
A. Spina bifida occulta
B. Myelomeningocele
C. Anencephaly
D. Tethered cord
E. Caudal regression syndrome
C. Anencephaly
A patient develops fragile skin after antibodies target proteins involved in cell-to-cell adhesion between keratinocytes. Which cellular structure is most directly affected?
Desmosomes
A newborn develops a scalp hemorrhage that can spread across the entire scalp and causes tachycardia and hypotension. Which layer has been injured?
A. Skin
B. Dense connective tissue
C. Galea aponeurotica
D. Loose areolar tissue
E. Pericranium
D. Loose areolar tissue
A patient has degeneration of the intervertebral disc. Which type of cartilage normally contributes to the disc's structure?
A. Hyaline cartilage
B. Elastic cartilage
C. Fibrocartilage
D. Articular cartilage
E. Epiphyseal cartilage
C. Fibrocartilage
A patient develops fluctuating skeletal muscle weakness that worsens with repeated activity. Autoantibodies interfere with postsynaptic nicotinic acetylcholine receptors. Which process is directly impaired?
A. Ca²⁺ binding to calmodulin
B. ACh release from the presynaptic terminal
C. Generation of the muscle action potential at the sarcolemma
D. Myosin ATP hydrolysis
E. Ca²⁺ reuptake into the SR
C. Generation of the muscle action potential at the sarcolemma
During embryologic development, cells migrate away from the dorsal neural tube and contribute to the formation of dorsal root ganglia. These cells are derived from:
A. Neural tube neuroepithelium
B. Surface ectoderm
C. Neural crest
D. Mesoderm
E. Endoderm
C. Neural crest
A mutation disrupts a protein that connects desmosomal cadherins to keratin intermediate filaments. Which cellular function would be most impaired?
A. Cell-to-basement membrane attachment
B. Resistance to mechanical shear
C. Cell-to-cell communication
D. Transcellular transport
E. Tightening of the paracellular barrier
B. Resistance to mechanical shear
A patient develops painful, flaccid bullae and erosions involving the oral mucosa. Biopsy demonstrates an intraepidermal blister caused by loss of keratinocyte adhesion. Autoantibodies are most likely directed against:
A. Type VII collagen
B. Hemidesmosomes
C. Desmoglein-3
D. Laminin
E. Integrins
C. Desmoglein-3
A patient with postmenopausal osteoporosis has increased bone resorption due to estrogen deficiency. Which molecular interaction is most directly responsible?
A. Increased OPG binding to RANKL
B. Decreased RANKL binding to RANK
C. Increased RANKL-mediated activation of osteoclasts
D. Increased calcitonin-mediated osteoclast activation
E. Decreased osteoclast differentiation due to M-CSF
C. Increased RANKL-mediated activation of osteoclasts
A patient develops severe muscle rigidity, hyperthermia, and increased CO₂ production shortly after administration of a volatile anesthetic. A mutation in which protein is most likely responsible?
A. Troponin C
B. RyR1
C. Myosin light chain
D. SERCA
E. Tropomyosin
B. RyR1
A pregnant patient asks about preventing neural tube defects. Which supplementation strategy is most appropriate for a patient with a previous pregnancy affected by a neural tube defect?
A. 0.1 mg folate beginning at 20 weeks
B. 0.4–0.8 mg folate beginning after conception
C. 4 mg folate beginning at least 1 month before conception
D. 10 mg folate beginning during the third trimester
E. Folate supplementation is unnecessary if prenatal vitamins are taken
C. 4 mg folate beginning at least 1 month before conception
A researcher observes two actin filaments connected at approximately 90° angles, producing a three-dimensional cortical network. Which actin-binding protein is most likely responsible?
A. Fimbrin
B. α-actinin
C. Filamin
D. Profilin
E. Tropomodulin
C. Filamin
A patient suffers a partial-thickness burn. Several weeks later, the injured area undergoes re-epithelialization without requiring a skin graft. Which surviving structure most directly allowed regeneration of the epidermis?
A. Stratum corneum
B. Stratum lucidum
C. Dermal collagen
D. Basal keratinocyte stem-cell population
E. Langerhans cells
D. Basal keratinocyte stem-cell population
A medication used to treat osteoporosis binds to RANKL and prevents it from activating osteoclast precursors. Which medication mechanism is being described?
A. Bisphosphonate-induced osteoclast apoptosis
B. Denosumab-mediated RANKL inhibition
C. PTH receptor blockade
D. Calcitonin receptor activation
E. Sclerostin activation
B. Denosumab-mediated RANKL inhibition
A patient with smooth muscle bronchoconstriction is given a β₂-adrenergic agonist. Which intracellular mechanism produces relaxation?
A. Gq → IP₃ → increased intracellular Ca²⁺
B. Gi → decreased cAMP
C. Gs → increased cAMP → activation of MLCP
D. Gs → decreased cAMP → activation of MLCK
E. Tyrosine kinase → increased Ca²⁺
C. Gs → increased cAMP → activation of MLCP
A 25-year-old patient sustains blunt trauma to the side of the skull. Several hours later, the patient develops loss of consciousness followed by a lucid interval and then rapid neurologic deterioration. Imaging demonstrates a biconvex lens-shaped hematoma. Which vessel was most likely injured?
A. Anterior cerebral artery
B. Middle meningeal artery
C. Superior sagittal sinus
D. Internal carotid artery
E. Great cerebral vein
B. Middle meningeal artery
A mutation prevents efficient activation of Arp2/3, resulting in impaired formation of branched actin networks. A child with this mutation develops eczema, recurrent infections, and thrombocytopenia. Which protein is most likely defective?
A. WASP
B. Ankyrin
C. Spectrin
D. Fimbrin
E. Cofilin
A. WASP
A patient develops a blistering disorder caused by autoantibodies against proteins responsible for anchoring basal keratinocytes to the basement membrane. Compared with pemphigus vulgaris, the blister in this disorder would most likely be located:
A. Within the stratum corneum
B. Within the stratum granulosum
C. Within the stratum spinosum
D. Between the epidermis and dermis
E. Within the dermis
D. Between the epidermis and dermis
A patient is immobilized for several months following a spinal cord injury. Increased expression of which osteocyte-derived molecule contributes to decreased bone formation during immobilization?
A. RANK
B. Osteocalcin
C. Sclerostin
D. Cathepsin K
E. M-CSF
C. Sclerostin
A mutation causes hypertrophic cardiomyopathy and is found in the gene encoding β-myosin heavy chain. Which cellular abnormality is most likely observed?
A. Loss of actin polymerization
B. Myofibrillar disarray
C. Failure of acetylcholine release
D. Destruction of intercalated discs
E. Loss of sarcomeres
B. Myofibrillar disarray
A newborn has a defect caused by abnormal secondary neurulation. Which finding would be most consistent with this embryologic error?
A. Anencephaly
B. Cranial neuropore failure
C. Myelomeningocele involving the cervical spinal cord
D. Tethered cord involving the caudal spinal cord
E. Failure of neural crest migration into the enteric nervous system
D. Tethered cord involving the caudal spinal cord