NBME HISTOLOGY 2026 FINAL
REGISTRY ADVANCED STRUCTURAL
AND CELL BIOLOGY SCENARIOS WITH
CORRECT VERIFIED ANSWERS AND
EXPLANATORY RATIONALES GRADE A+
CERTIFIED & INSTANT DOWNLOAD
1. A researcher is studying the structural components of the
extracellular matrix in a laboratory. Under transmission electron
microscopy (TEM), they observe long, unbranched polysaccharide
chains composed of repeating disaccharide units that are highly
negatively charged due to sulfate and carboxyl groups. These
molecules are found covalently linked to a core protein, forming a
giant aggregate that retains significant amounts of water. What is
the primary function of these specific extracellular structures in
cartilage tissue?
A. Providing high tensile strength to resist pulling forces
B. Resisting compression and providing a smooth, low-
friction surface
C. Mediating cell adhesion to the basement membrane via
integrins
D. Facilitating rapid cell migration during acute inflammation
Correct Answer: B
Rationale: The description refers to proteoglycans, which are
composed of glycosaminoglycans (GAGs) attached to a core
protein. Because of their dense negative charges, they attract
sodium ions and osmotically draw in water, forming a hydrated
gel. In cartilage, this hydration allows the tissue to resist
compressive forces and provides a smooth surface for joint
articulation. Collagen fibers (primarily Type II in cartilage)
provide tensile strength. Fibronectin and laminin mediate cell
adhesion.
2. A 4,000g infant is delivered to a 34-year-old female at 39 weeks'
gestation. Within hours of birth, the newborn develops severe
respiratory distress with tachypnea, grunting, and intercostal
, retractions. A chest radiograph demonstrates diffuse, ground-glass
opacities and atelectasis. The infant is diagnosed with neonatal
respiratory distress syndrome (NRDS). This condition is primarily
caused by the structural dysfunction or quantitative deficiency of a
lipid-protein complex produced by cells with which of the
following histological characteristics?
A. Simple squamous cells with attenuated cytoplasm forming the
blood-air barrier
B. Cuboidal cells with apical microvilli and lamellar
bodies containing concentric phospholipid whorls
C. Columnar ciliated cells with basal bodies that propel mucus
cranially
D. Pyramidal cells containing extensive rough endoplasmic
reticulum and dense zymogen granules
Correct Answer: B
Rationale: Neonatal respiratory distress syndrome is caused by a
deficiency of pulmonary surfactant, which is synthesized and
secreted by Type II pneumocytes. Histologically, Type II
pneumocytes are cuboidal cells that contain characteristic
lamellar bodies—membrane-bound organelles containing
concentric lamellae of phospholipids. Type I pneumocytes are
simple squamous cells responsible for gas exchange. Ciliated cells
are found in the conducting airways, not the alveoli.
3. A 4-year-old boy is brought to the pediatrician due to recurrent
skin infections, fragile skin, and delayed wound healing. On
physical examination, the child exhibits hyperelastic skin and
hypermobile joints. Genetic testing reveals a mutation in the
COL5A1 gene, confirming a diagnosis of Ehlers-Danlos syndrome
(classic type). The structural integrity of the affected tissue is
compromised because of a defect in a protein that normally
displays which of the following architectural features?
A. A single alpha-helix stabilized by intra-chain hydrogen bonds
between every fourth amino acid
B. A beta-pleated sheet composed of anti-parallel polypeptide
strands
C. A triple helix composed of three alpha-chains rich in
glycine, proline, and hydroxyproline
D. An amorphous network of tropoelastin cross-linked by
desmosine and isodesmosine
Correct Answer: C
, Rationale: Collagen is characterized by a triple-helix quaternary
structure formed by three polypeptide alpha-chains. Every third
amino acid is glycine because its small size (a single hydrogen
atom side chain) allows it to fit into the tight central core of the
helix. Proline and hydroxyproline stabilize the helix. Classic
Ehlers-Danlos syndrome involves defects in Type V collagen,
disrupting triple helix assembly. Elastin forms an amorphous
network cross-linked by desmosine.
4. A 62-year-old male presenting with chronic progressive back pain
undergoes a biopsy of a osteolytic vertebral lesion. Histological
analysis of the bone tissue reveals an abundance of large, motile,
multinucleated cells situated within shallow depressions along the
bone surface known as Howship's lacunae. At the ultra-structural
level, these cells exhibit a highly folded plasma membrane facing
the bone matrix. What is the primary mechanism by which these
cells dissolve the mineralized component of the bone matrix?
A. Exocytosis of alkaline phosphatase to increase local phosphate
concentration
B. Secretion of Type I collagenase into the osteoid layer
C. Active pumping of hydrogen ions via H+-ATPase
pumps into a sealed subosteoclastic compartment
D. Phagocytosis of hydroxyapatite crystals followed by intracellular
lysosomal degradation
Correct Answer: C
Rationale: The cells described are osteoclasts, which are derived
from the monocyte-macrophage lineage and are responsible for
bone resorption. They reside in Howship's lacunae and use a
specialized "ruffled border" (folded plasma membrane) to secrete
hydrochloric acid and lysosomal enzymes (like cathepsin K) into a
sealed extracellular compartment. The acid dissolves
hydroxyapatite crystals, while enzymes degrade the organic
matrix. Alkaline phosphatase is secreted by osteoblasts to
promote mineralization.
5. A 22-year-old female presents with persistent diarrhea, bloating,
and weight loss. Serological testing is positive for anti-tissue
transglutaminase (anti-tTG) IgA antibodies, and a duodenal biopsy
is performed. Microscopic examination of the tissue reveals
marked villous atrophy, crypt hyperplasia, and a dense infiltrate of
intraepithelial lymphocytes. In a healthy duodenum, the simple
, columnar epithelial cells lining the villi are specialized to maximize
absorption via modifications that contain a structural core
composed of which of the following cytoskeletal elements?
A. Microfilaments made of actin bundles cross-linked by
fimbrin and villin
B. Protofilaments of alpha- and beta-tubulin arranged in a 9+2
doublet pattern
C. Intermediate filaments composed of cytokeratin networks
anchored to desmosomes
D. Thick filaments composed of myosin heavy and light chains
Correct Answer: A
Rationale: The simple columnar cells of the intestinal mucosa
contain microvilli on their apical surface, collectively forming the
brush border to increase surface area for absorption. The core of
each microvillus is composed of a rigid bundle of actin
microfilaments cross-linked by the proteins fimbrin and villin.
Tubulin arranged in a 9+2 pattern describes cilia or flagella,
which are motile structures. Cytokeratin intermediate filaments
provide structural stability to the epithelium but do not form the
core of microvilli.
6. A 54-year-old male with a history of severe atherosclerotic
cardiovascular disease undergoes an elective coronary artery
bypass graft (CABG). During the harvesting of the great saphenous
vein, the surgical pathology team examines a cross-section of the
vessel wall. Which of the following histological features best
distinguishes this large vein from an elastic artery of comparable
diameter?
A. A highly prominent tunica media rich in concentric fenestrated
elastic lamellae
B. The presence of an internal elastic lamina separating the tunica
intima from the tunica media
C. A poorly defined tunica media and a thick, well-
developed tunica adventitia containing longitudinal
smooth muscle bundles
D. An endothelium composed of stratified cuboidal cells lacking a
basement membrane
Correct Answer: C
Rationale: Veins have lower pressure systems compared to
arteries. Consequently, veins have a much thinner tunica media
with less smooth muscle and elastic tissue, and a thick, prominent
REGISTRY ADVANCED STRUCTURAL
AND CELL BIOLOGY SCENARIOS WITH
CORRECT VERIFIED ANSWERS AND
EXPLANATORY RATIONALES GRADE A+
CERTIFIED & INSTANT DOWNLOAD
1. A researcher is studying the structural components of the
extracellular matrix in a laboratory. Under transmission electron
microscopy (TEM), they observe long, unbranched polysaccharide
chains composed of repeating disaccharide units that are highly
negatively charged due to sulfate and carboxyl groups. These
molecules are found covalently linked to a core protein, forming a
giant aggregate that retains significant amounts of water. What is
the primary function of these specific extracellular structures in
cartilage tissue?
A. Providing high tensile strength to resist pulling forces
B. Resisting compression and providing a smooth, low-
friction surface
C. Mediating cell adhesion to the basement membrane via
integrins
D. Facilitating rapid cell migration during acute inflammation
Correct Answer: B
Rationale: The description refers to proteoglycans, which are
composed of glycosaminoglycans (GAGs) attached to a core
protein. Because of their dense negative charges, they attract
sodium ions and osmotically draw in water, forming a hydrated
gel. In cartilage, this hydration allows the tissue to resist
compressive forces and provides a smooth surface for joint
articulation. Collagen fibers (primarily Type II in cartilage)
provide tensile strength. Fibronectin and laminin mediate cell
adhesion.
2. A 4,000g infant is delivered to a 34-year-old female at 39 weeks'
gestation. Within hours of birth, the newborn develops severe
respiratory distress with tachypnea, grunting, and intercostal
, retractions. A chest radiograph demonstrates diffuse, ground-glass
opacities and atelectasis. The infant is diagnosed with neonatal
respiratory distress syndrome (NRDS). This condition is primarily
caused by the structural dysfunction or quantitative deficiency of a
lipid-protein complex produced by cells with which of the
following histological characteristics?
A. Simple squamous cells with attenuated cytoplasm forming the
blood-air barrier
B. Cuboidal cells with apical microvilli and lamellar
bodies containing concentric phospholipid whorls
C. Columnar ciliated cells with basal bodies that propel mucus
cranially
D. Pyramidal cells containing extensive rough endoplasmic
reticulum and dense zymogen granules
Correct Answer: B
Rationale: Neonatal respiratory distress syndrome is caused by a
deficiency of pulmonary surfactant, which is synthesized and
secreted by Type II pneumocytes. Histologically, Type II
pneumocytes are cuboidal cells that contain characteristic
lamellar bodies—membrane-bound organelles containing
concentric lamellae of phospholipids. Type I pneumocytes are
simple squamous cells responsible for gas exchange. Ciliated cells
are found in the conducting airways, not the alveoli.
3. A 4-year-old boy is brought to the pediatrician due to recurrent
skin infections, fragile skin, and delayed wound healing. On
physical examination, the child exhibits hyperelastic skin and
hypermobile joints. Genetic testing reveals a mutation in the
COL5A1 gene, confirming a diagnosis of Ehlers-Danlos syndrome
(classic type). The structural integrity of the affected tissue is
compromised because of a defect in a protein that normally
displays which of the following architectural features?
A. A single alpha-helix stabilized by intra-chain hydrogen bonds
between every fourth amino acid
B. A beta-pleated sheet composed of anti-parallel polypeptide
strands
C. A triple helix composed of three alpha-chains rich in
glycine, proline, and hydroxyproline
D. An amorphous network of tropoelastin cross-linked by
desmosine and isodesmosine
Correct Answer: C
, Rationale: Collagen is characterized by a triple-helix quaternary
structure formed by three polypeptide alpha-chains. Every third
amino acid is glycine because its small size (a single hydrogen
atom side chain) allows it to fit into the tight central core of the
helix. Proline and hydroxyproline stabilize the helix. Classic
Ehlers-Danlos syndrome involves defects in Type V collagen,
disrupting triple helix assembly. Elastin forms an amorphous
network cross-linked by desmosine.
4. A 62-year-old male presenting with chronic progressive back pain
undergoes a biopsy of a osteolytic vertebral lesion. Histological
analysis of the bone tissue reveals an abundance of large, motile,
multinucleated cells situated within shallow depressions along the
bone surface known as Howship's lacunae. At the ultra-structural
level, these cells exhibit a highly folded plasma membrane facing
the bone matrix. What is the primary mechanism by which these
cells dissolve the mineralized component of the bone matrix?
A. Exocytosis of alkaline phosphatase to increase local phosphate
concentration
B. Secretion of Type I collagenase into the osteoid layer
C. Active pumping of hydrogen ions via H+-ATPase
pumps into a sealed subosteoclastic compartment
D. Phagocytosis of hydroxyapatite crystals followed by intracellular
lysosomal degradation
Correct Answer: C
Rationale: The cells described are osteoclasts, which are derived
from the monocyte-macrophage lineage and are responsible for
bone resorption. They reside in Howship's lacunae and use a
specialized "ruffled border" (folded plasma membrane) to secrete
hydrochloric acid and lysosomal enzymes (like cathepsin K) into a
sealed extracellular compartment. The acid dissolves
hydroxyapatite crystals, while enzymes degrade the organic
matrix. Alkaline phosphatase is secreted by osteoblasts to
promote mineralization.
5. A 22-year-old female presents with persistent diarrhea, bloating,
and weight loss. Serological testing is positive for anti-tissue
transglutaminase (anti-tTG) IgA antibodies, and a duodenal biopsy
is performed. Microscopic examination of the tissue reveals
marked villous atrophy, crypt hyperplasia, and a dense infiltrate of
intraepithelial lymphocytes. In a healthy duodenum, the simple
, columnar epithelial cells lining the villi are specialized to maximize
absorption via modifications that contain a structural core
composed of which of the following cytoskeletal elements?
A. Microfilaments made of actin bundles cross-linked by
fimbrin and villin
B. Protofilaments of alpha- and beta-tubulin arranged in a 9+2
doublet pattern
C. Intermediate filaments composed of cytokeratin networks
anchored to desmosomes
D. Thick filaments composed of myosin heavy and light chains
Correct Answer: A
Rationale: The simple columnar cells of the intestinal mucosa
contain microvilli on their apical surface, collectively forming the
brush border to increase surface area for absorption. The core of
each microvillus is composed of a rigid bundle of actin
microfilaments cross-linked by the proteins fimbrin and villin.
Tubulin arranged in a 9+2 pattern describes cilia or flagella,
which are motile structures. Cytokeratin intermediate filaments
provide structural stability to the epithelium but do not form the
core of microvilli.
6. A 54-year-old male with a history of severe atherosclerotic
cardiovascular disease undergoes an elective coronary artery
bypass graft (CABG). During the harvesting of the great saphenous
vein, the surgical pathology team examines a cross-section of the
vessel wall. Which of the following histological features best
distinguishes this large vein from an elastic artery of comparable
diameter?
A. A highly prominent tunica media rich in concentric fenestrated
elastic lamellae
B. The presence of an internal elastic lamina separating the tunica
intima from the tunica media
C. A poorly defined tunica media and a thick, well-
developed tunica adventitia containing longitudinal
smooth muscle bundles
D. An endothelium composed of stratified cuboidal cells lacking a
basement membrane
Correct Answer: C
Rationale: Veins have lower pressure systems compared to
arteries. Consequently, veins have a much thinner tunica media
with less smooth muscle and elastic tissue, and a thick, prominent
