NBME EXAM QUESTIONS WITH CORRECT
ANSWERS AND RATIONALES 2025/2026
1
Exam Section 1: Item 1 of 50
National Board of Medical Examiners'
Comprehensive Basic Science Self-Assessment
1. Patients with prolonged starvation or untreated type 1 diabetes mellitus overproduce ketone
bodies. Which of the following is a common factor that is responsible for ketosis in patients with
these two conditions?
A) Depletion of pentose phosphate pathway intermediates
B) Increased availability of acetyl COA
C) Inhibition of fatty acid oxidation
D) Inhibition of gluconeogenesis
E) Inhibition of glycogenolysis - CORRECT ANSWER -B.
Increased availability of acetyl CoA is common to states of starvation and untreated type 1
diabetes mellitus. In starvation, glycogen stores are gradually depleted. The body then relies on
the
breakdown of fat through oxidation of fatty acids to provide energy. Fatty acid oxidation occurs
in the mitochondria of the cell. In each cycle of oxidation, two-carbon fragments are cleaved to
form
acetyl CoA, which leaves the mitochondria via the carnitine shuttle. In addition to a molecule of
acetyl CoA which then enters the citric acid cycle, a molecule of NADH is produced in each cycle.
Ketogenesis occurs in starvation via two-carbon fragments, with formation of ketoacids such as
acetoacetyl CoA and B-hydroxybutyrate. The ability to generate energy from adipose during a
period of starvation is critical to maintaining the function of vital organs, such as the brain. In
untreated type 1 diabetes mellitus, there is an absolute deficiency of insulin, which renders
many
cells incapable of shuttling glucose into the cell for use in cellular respiration. While there are
several glucose transporters that do not require insulin for glucose entry, GLUT4 is commonly
,expressed in many cell types and requires insulin to function. Patients with untreated type 1
diabetes mellitus will have serum glucose concentrations in the high-normal to high range as a
result
of ongoing gluconeogenesis and glycogenolysis, but insulin deficiency prevents entry of
circulating glucose into cells through glucose transport proteins, effectively resulting in a state of
starvation. This results in ketogenesis and accounts for the presence of ketone bodies in the
blood and urine of patients with starvation or untreated type 1 diabetes mellitus.
Incorrect Answers: A, C, D, and E.
Depletion of pentose phosphate pathway intermediates (Choice A) is not correct.
2
Exam Section 1: Item 2 of 50
National Board of Medical Examiners'
Comprehensive Basic Science Self-Assessment
2. A 65-year-old man comes to the emergency department because of a 1-week history of blood
in his sputum. A mass is found on a radiograph. Bronchoscopy is planned. In order to pass the
bronchoscope through the oropharynx to the lungs without eliciting a gag reflex, the pharynx is
anesthetized. The afferent limb of the reflex is most likely to be blocked by anesthesia to which
of the following cranial nerves?
A) Trigeminal
B) Facial
C) Glossopharyngeal
D) Vagus
E) Hypoglossal - CORRECT ANSWER -C.
The glossopharyngeal nerve (cranial nerve IX) contains somatic afferent fibers that control the
sensation of the palate and upper pharynx, providing afferent information for the gag reflex.
The
,efferent nerve for the gag reflex is the vagus nerve, which innervates the soft palate and
pharyngeal muscles to control gagging and swallowing. In addition to its role in the gag reflex,
the
glossopharyngeal nerve contains other afferent and efferent nerve fibers. Components of the
glossopharyngeal nerve include general visceral afferent fibers (carotid body and sinus chemo-
and
baroreceptors), special sensory fibers (taste from posterior third of the tongue), general visceral
efferent fibers (parasympathetic innervation of the parotid gland), and special visceral efferent
fibers (stylopharyngeus muscle). Lesions of the glossopharyngeal nerve lead to impaired
sensation and taste in the posterior third of the tongue, impaired sensation of the palate and
pharynx,
parotid gland dysfunction, difficulty swallowing, and an absent gag reflex.
Incorrect Answers: A, B, D, and E.
The trigeminal nerve (Choice A), or cranial nerve V, provides somatic sensory innervation to the
face and scalp. The mandibular nerve (the V3 branch of the trigeminal nerve) additionally
controls
the muscles of mastication and mediates pain and temperature sensation in the anterior two-
thirds of the tongue. The trigeminal nerve does not innervate the pharynx.
The facial nerve (Choice B), or cranial nerve VII, contains afferent and efferent fibers that carry
somatic and visceral information. Motor axons innervate the muscles of facial expression and
the
stapedius muscle, while sensory axons innervate the outer ear and mediate taste sensation
from the anterior two-thirds of the tongue. The facial nerve does not innervate the pharynx.
The vagus nerve (Choice D),
3
Exam Section 1: Item 3 of 50
National Board of Medical Examiners'
Comprehensive Basic Science Self-Assessment
, 3. A 62-year-old man with a 4-year history of chronic angina pectoris comes to the emergency
department because of severe chest and left shoulder pain. Physical examination shows
bradycardia. An ECG shows ST-segment elevation in leads II, III, and aVF. Occlusion of blood flow
in which of the following arteries is the most likely cause of the findings in this patient?
A) Anterior interventricular (left anterior descending)
B) Circumflex
C) Left coronary
D) Right coronary - CORRECT ANSWER -D.
The right coronary artery originates from the right aortic sinus and primarily provides blood
flow to the right ventricle, right atrium, sinoatrial (SA) node, and atrioventricular (AV) node, and
in a
right-dominant circulation (-85% of patients), it provides a majority of the blood supply to the
inferior heart through the posterior descending artery. Occlusion of the right coronary artery
can
result in infarction of myocardial tissue along the inferior portion of the heart, which leads to ST-
segment changes in the inferior ECG leads II, III, and aVF. Impaired perfusion to the SA and AV
nodes can also result in bradycardia or heart block. The patient requires admission to the
hospital and emergent cardiac catheterization for revascularization or consideration of
thrombolytics if
not close to a center capable of percutaneous coronary intervention.
Incorrect Answers: A, B, and C.
The anterior interventricular (left anterior descending) (Choice A) artery branches from the left
main coronary artery and provides perfusion to the anterior portion of the interventricular
septum,
the anterior left ventricle, and the anterolateral papillary muscle. Infarction of this territory may
present with ST-segment changes in the precordial ECCG leads.
The circumflex (Choice B) artery originates from the left main coronary artery and primarily
provides perfusion to the lateral and posterior walls of the left ventricle, the anterolateral
papillary
muscle, and some blood flow to the AV node. It does not provide perfusion to the inferior heart
unless the patient demonstrates a left-dominant circulation (~8% of patients). Infarction of this
ANSWERS AND RATIONALES 2025/2026
1
Exam Section 1: Item 1 of 50
National Board of Medical Examiners'
Comprehensive Basic Science Self-Assessment
1. Patients with prolonged starvation or untreated type 1 diabetes mellitus overproduce ketone
bodies. Which of the following is a common factor that is responsible for ketosis in patients with
these two conditions?
A) Depletion of pentose phosphate pathway intermediates
B) Increased availability of acetyl COA
C) Inhibition of fatty acid oxidation
D) Inhibition of gluconeogenesis
E) Inhibition of glycogenolysis - CORRECT ANSWER -B.
Increased availability of acetyl CoA is common to states of starvation and untreated type 1
diabetes mellitus. In starvation, glycogen stores are gradually depleted. The body then relies on
the
breakdown of fat through oxidation of fatty acids to provide energy. Fatty acid oxidation occurs
in the mitochondria of the cell. In each cycle of oxidation, two-carbon fragments are cleaved to
form
acetyl CoA, which leaves the mitochondria via the carnitine shuttle. In addition to a molecule of
acetyl CoA which then enters the citric acid cycle, a molecule of NADH is produced in each cycle.
Ketogenesis occurs in starvation via two-carbon fragments, with formation of ketoacids such as
acetoacetyl CoA and B-hydroxybutyrate. The ability to generate energy from adipose during a
period of starvation is critical to maintaining the function of vital organs, such as the brain. In
untreated type 1 diabetes mellitus, there is an absolute deficiency of insulin, which renders
many
cells incapable of shuttling glucose into the cell for use in cellular respiration. While there are
several glucose transporters that do not require insulin for glucose entry, GLUT4 is commonly
,expressed in many cell types and requires insulin to function. Patients with untreated type 1
diabetes mellitus will have serum glucose concentrations in the high-normal to high range as a
result
of ongoing gluconeogenesis and glycogenolysis, but insulin deficiency prevents entry of
circulating glucose into cells through glucose transport proteins, effectively resulting in a state of
starvation. This results in ketogenesis and accounts for the presence of ketone bodies in the
blood and urine of patients with starvation or untreated type 1 diabetes mellitus.
Incorrect Answers: A, C, D, and E.
Depletion of pentose phosphate pathway intermediates (Choice A) is not correct.
2
Exam Section 1: Item 2 of 50
National Board of Medical Examiners'
Comprehensive Basic Science Self-Assessment
2. A 65-year-old man comes to the emergency department because of a 1-week history of blood
in his sputum. A mass is found on a radiograph. Bronchoscopy is planned. In order to pass the
bronchoscope through the oropharynx to the lungs without eliciting a gag reflex, the pharynx is
anesthetized. The afferent limb of the reflex is most likely to be blocked by anesthesia to which
of the following cranial nerves?
A) Trigeminal
B) Facial
C) Glossopharyngeal
D) Vagus
E) Hypoglossal - CORRECT ANSWER -C.
The glossopharyngeal nerve (cranial nerve IX) contains somatic afferent fibers that control the
sensation of the palate and upper pharynx, providing afferent information for the gag reflex.
The
,efferent nerve for the gag reflex is the vagus nerve, which innervates the soft palate and
pharyngeal muscles to control gagging and swallowing. In addition to its role in the gag reflex,
the
glossopharyngeal nerve contains other afferent and efferent nerve fibers. Components of the
glossopharyngeal nerve include general visceral afferent fibers (carotid body and sinus chemo-
and
baroreceptors), special sensory fibers (taste from posterior third of the tongue), general visceral
efferent fibers (parasympathetic innervation of the parotid gland), and special visceral efferent
fibers (stylopharyngeus muscle). Lesions of the glossopharyngeal nerve lead to impaired
sensation and taste in the posterior third of the tongue, impaired sensation of the palate and
pharynx,
parotid gland dysfunction, difficulty swallowing, and an absent gag reflex.
Incorrect Answers: A, B, D, and E.
The trigeminal nerve (Choice A), or cranial nerve V, provides somatic sensory innervation to the
face and scalp. The mandibular nerve (the V3 branch of the trigeminal nerve) additionally
controls
the muscles of mastication and mediates pain and temperature sensation in the anterior two-
thirds of the tongue. The trigeminal nerve does not innervate the pharynx.
The facial nerve (Choice B), or cranial nerve VII, contains afferent and efferent fibers that carry
somatic and visceral information. Motor axons innervate the muscles of facial expression and
the
stapedius muscle, while sensory axons innervate the outer ear and mediate taste sensation
from the anterior two-thirds of the tongue. The facial nerve does not innervate the pharynx.
The vagus nerve (Choice D),
3
Exam Section 1: Item 3 of 50
National Board of Medical Examiners'
Comprehensive Basic Science Self-Assessment
, 3. A 62-year-old man with a 4-year history of chronic angina pectoris comes to the emergency
department because of severe chest and left shoulder pain. Physical examination shows
bradycardia. An ECG shows ST-segment elevation in leads II, III, and aVF. Occlusion of blood flow
in which of the following arteries is the most likely cause of the findings in this patient?
A) Anterior interventricular (left anterior descending)
B) Circumflex
C) Left coronary
D) Right coronary - CORRECT ANSWER -D.
The right coronary artery originates from the right aortic sinus and primarily provides blood
flow to the right ventricle, right atrium, sinoatrial (SA) node, and atrioventricular (AV) node, and
in a
right-dominant circulation (-85% of patients), it provides a majority of the blood supply to the
inferior heart through the posterior descending artery. Occlusion of the right coronary artery
can
result in infarction of myocardial tissue along the inferior portion of the heart, which leads to ST-
segment changes in the inferior ECG leads II, III, and aVF. Impaired perfusion to the SA and AV
nodes can also result in bradycardia or heart block. The patient requires admission to the
hospital and emergent cardiac catheterization for revascularization or consideration of
thrombolytics if
not close to a center capable of percutaneous coronary intervention.
Incorrect Answers: A, B, and C.
The anterior interventricular (left anterior descending) (Choice A) artery branches from the left
main coronary artery and provides perfusion to the anterior portion of the interventricular
septum,
the anterior left ventricle, and the anterolateral papillary muscle. Infarction of this territory may
present with ST-segment changes in the precordial ECCG leads.
The circumflex (Choice B) artery originates from the left main coronary artery and primarily
provides perfusion to the lateral and posterior walls of the left ventricle, the anterolateral
papillary
muscle, and some blood flow to the AV node. It does not provide perfusion to the inferior heart
unless the patient demonstrates a left-dominant circulation (~8% of patients). Infarction of this
