NBME 30 | QUESTIONS AND ANSWERS | 2026 UPDATE
| WITH COMPLETE SOLUTION.
1
Exam Section 1: Item 1 of 50
National Board of Medical Examiners®
Comprehensive Basic Science Self-Assessment
1. Shortly after delivery, a full-term male newborn is found to have black hair
with a white forelock. His mother, a brunette, also has a white forelock and
wears hearing aids. Physical examination shows heterochromia of irides.
Otoacoustic emissions testing and
brain stem auditory evoked responses show bilateral sensorineural hearing
loss. Which of the following is the most likely cause of the findings in this
patient?
A) Abnormal neural crest development
B) Abnormality of connexins
C) Deficiency of homogentisic acid oxidase activity
D) Deficiency of tyrosinase activity
E) Failure of internalization of melanin granules by keratinocytes
F) Failure of melanosome transportation along dendrites Answer - A.
Abnormal neural crest development leads to Waardenburg syndrome.
Waardenburg syndrome is a syndrome of patchy depigmentation of the skin,
hair, irises, and cochlear dysfunction that primarily illustrates an autosomal
dominant inheritance pattern. Because of
genetic mutations of genes encoding transcription factors, neural crest cells do
not properly differentiate into melanoblasts (melanocyte precursors), or
,melanoblasts do not migrate to their appropriate location. Patients typically
have a white forelock and eyelashes,
depigmented skin patches, iridic heterochromia, and sensorineural deafness.
The eyes may also be laterally displaced. The clinical diagnosis may be
confirmed with genetic testing. Treatment includes audiologic evaluation and
genetic consultation.
Incorrect Answers: B, C, D, E, and F.
An abnormality of connexins (Choice B) would lead to abnormal formation of
the plasma membrane channels of diverse cell types. Different combinations of
sensorineural hearing loss, ichthyosis, alopecia, and peripheral neuropathy may
occur. Depigmentation
would be atypical.
Deficiency of homogentisic acid oxidase activity (Choice C) would lead to
decreased metabolism of the amino acids phenylalanine and tyrosine, which
instead degrade into homogentisic acid. Homogentisic acid accumulates in the
skin and joints, causing increased
pigmentation and arthritis, respectively. Depigmentation would be atypical.
Deficiency of tyrosinase activity (Choice D) occurs in oculocutaneous albinism,
which presents with uniformly hypopigmented hair and skin (versus the patchy
depigmentation of Waardenburg syndrome) and eye abnormalities (eg, iris
hypopigmentation, refractive
errors, nystagmus). In tyrosinase deficiency, melanocytes are unable to
synthesize melanin from the amino acid tyrosine. Iridic heterochromia and
sensorineural deafnes
2
Exam Section 1: Item 2 of 50
National Board of Medical Examiners®
Comprehensive Basic Science Self-Assessment
2. During an experiment, a solution of mixed fatty acids is injected into the
duodenum of an experimental animal. Under these conditions, the clearance
,rate of an intravenous glucose load from the circulation is doubled. In contrast,
an injection of an equal
volume amount of 0.9% saline into the duodenum has much less effect on the
plasma clearance rate of glucose. These findings are most likely caused by the
secretion of which of the following hormones?
A) Gastrin
B) Glucose-dependent insulinotropic peptide
C) Motilin
D) Secretin
E) Somatostatin Answer - B.
Glucose-dependent insulinotropic peptide (GIP) is secreted by K cells in the
duodenum and jejunum and functions to decrease gastric acid production and
stimulate insulin release from the pancreas. Its secretion is promoted by the
presence of fatty acids, amino
acids, and intestinal glucose. While serum glucose also stimulates insulin
secretion by the pancreas, the effect of intraluminal glucose on GIP and
subsequent insulin secretion leads to increased concentrations of insulin
compared to parenteral glucose
administration. Insulin promotes peripheral tissue uptake of glucose, glycolysis,
glycogen synthesis, protein synthesis, and fatty acid synthesis, resulting in
decreased glucose concentration in the serum.
Incorrect Answers: A, C, D, and E.
Gastrin (Choice A) is produced by G cells in the gastric antrum and stimulates
parietal cells within the gastric body to produce hydrochloric acid. Gastric acid
has no effect on serum glucose concentration.
Motilin (Choice C) is secreted by the small intestine and stimulates intestinal
peristalsis. Motilin receptors are targeted by erythromycin and
metoclopramide, used therapeutically in gastroparesis.
Secretin (Choice D) is produced by duodenal S cells. It promotes the release of
bicarbonate-rich pancreatic secretions and bile and inhibits gastric acid
production.
, Somatostatin (Choice E) is a regulatory peptide secreted by D cells of the
pancreas and gastrointestinal mucosa that inhibits gastric acid and pepsinogen
secretion, gallbladder contraction, and insulin and glucagon release.
Somatostatin would have an indirect
effect on glucose through counterregulatory action of both insulin and
glucagon.
Educational Objective: Glucose-dependent insulinotropic peptide (GIP) is
secreted by K cells in the duodenum and jejunum, and it functions to decrease
gastric acid production and
3
Exam Section 1: Item 3 of 50
National Board of Medical Examiners®
Comprehensive Basic Science Self-Assessment
3. A 53-year-old man comes to the physician because of a 6-day history of
shortness of breath, cough, and pleuritic chest pain. His temperature is 38.9°C
(102°F), and respirations are 35/min. Sputum is purulent and rust colored.
Physical examination shows
decreased breath sounds, and crackles are heard at the left base. A Gram stain
of sputum shows gram-positive diplococci. A chest x-ray shows left-sided lobar
consolidation. Which of the following anatomic structures most likely allowed
rapid spread of
organisms between alveoli to involve the entire left lobe in this patient?
A) Alveolar capillaries
B) Germinal centers
C) Lymphatic capillaries
D) Pores of Kohn
E) Vascular sinusoids Answer - D.
The pores of Kohn form connections between alveoli and are present in normal
lung tissue. They are composed, at least in part, of type Il alveolar cells and
| WITH COMPLETE SOLUTION.
1
Exam Section 1: Item 1 of 50
National Board of Medical Examiners®
Comprehensive Basic Science Self-Assessment
1. Shortly after delivery, a full-term male newborn is found to have black hair
with a white forelock. His mother, a brunette, also has a white forelock and
wears hearing aids. Physical examination shows heterochromia of irides.
Otoacoustic emissions testing and
brain stem auditory evoked responses show bilateral sensorineural hearing
loss. Which of the following is the most likely cause of the findings in this
patient?
A) Abnormal neural crest development
B) Abnormality of connexins
C) Deficiency of homogentisic acid oxidase activity
D) Deficiency of tyrosinase activity
E) Failure of internalization of melanin granules by keratinocytes
F) Failure of melanosome transportation along dendrites Answer - A.
Abnormal neural crest development leads to Waardenburg syndrome.
Waardenburg syndrome is a syndrome of patchy depigmentation of the skin,
hair, irises, and cochlear dysfunction that primarily illustrates an autosomal
dominant inheritance pattern. Because of
genetic mutations of genes encoding transcription factors, neural crest cells do
not properly differentiate into melanoblasts (melanocyte precursors), or
,melanoblasts do not migrate to their appropriate location. Patients typically
have a white forelock and eyelashes,
depigmented skin patches, iridic heterochromia, and sensorineural deafness.
The eyes may also be laterally displaced. The clinical diagnosis may be
confirmed with genetic testing. Treatment includes audiologic evaluation and
genetic consultation.
Incorrect Answers: B, C, D, E, and F.
An abnormality of connexins (Choice B) would lead to abnormal formation of
the plasma membrane channels of diverse cell types. Different combinations of
sensorineural hearing loss, ichthyosis, alopecia, and peripheral neuropathy may
occur. Depigmentation
would be atypical.
Deficiency of homogentisic acid oxidase activity (Choice C) would lead to
decreased metabolism of the amino acids phenylalanine and tyrosine, which
instead degrade into homogentisic acid. Homogentisic acid accumulates in the
skin and joints, causing increased
pigmentation and arthritis, respectively. Depigmentation would be atypical.
Deficiency of tyrosinase activity (Choice D) occurs in oculocutaneous albinism,
which presents with uniformly hypopigmented hair and skin (versus the patchy
depigmentation of Waardenburg syndrome) and eye abnormalities (eg, iris
hypopigmentation, refractive
errors, nystagmus). In tyrosinase deficiency, melanocytes are unable to
synthesize melanin from the amino acid tyrosine. Iridic heterochromia and
sensorineural deafnes
2
Exam Section 1: Item 2 of 50
National Board of Medical Examiners®
Comprehensive Basic Science Self-Assessment
2. During an experiment, a solution of mixed fatty acids is injected into the
duodenum of an experimental animal. Under these conditions, the clearance
,rate of an intravenous glucose load from the circulation is doubled. In contrast,
an injection of an equal
volume amount of 0.9% saline into the duodenum has much less effect on the
plasma clearance rate of glucose. These findings are most likely caused by the
secretion of which of the following hormones?
A) Gastrin
B) Glucose-dependent insulinotropic peptide
C) Motilin
D) Secretin
E) Somatostatin Answer - B.
Glucose-dependent insulinotropic peptide (GIP) is secreted by K cells in the
duodenum and jejunum and functions to decrease gastric acid production and
stimulate insulin release from the pancreas. Its secretion is promoted by the
presence of fatty acids, amino
acids, and intestinal glucose. While serum glucose also stimulates insulin
secretion by the pancreas, the effect of intraluminal glucose on GIP and
subsequent insulin secretion leads to increased concentrations of insulin
compared to parenteral glucose
administration. Insulin promotes peripheral tissue uptake of glucose, glycolysis,
glycogen synthesis, protein synthesis, and fatty acid synthesis, resulting in
decreased glucose concentration in the serum.
Incorrect Answers: A, C, D, and E.
Gastrin (Choice A) is produced by G cells in the gastric antrum and stimulates
parietal cells within the gastric body to produce hydrochloric acid. Gastric acid
has no effect on serum glucose concentration.
Motilin (Choice C) is secreted by the small intestine and stimulates intestinal
peristalsis. Motilin receptors are targeted by erythromycin and
metoclopramide, used therapeutically in gastroparesis.
Secretin (Choice D) is produced by duodenal S cells. It promotes the release of
bicarbonate-rich pancreatic secretions and bile and inhibits gastric acid
production.
, Somatostatin (Choice E) is a regulatory peptide secreted by D cells of the
pancreas and gastrointestinal mucosa that inhibits gastric acid and pepsinogen
secretion, gallbladder contraction, and insulin and glucagon release.
Somatostatin would have an indirect
effect on glucose through counterregulatory action of both insulin and
glucagon.
Educational Objective: Glucose-dependent insulinotropic peptide (GIP) is
secreted by K cells in the duodenum and jejunum, and it functions to decrease
gastric acid production and
3
Exam Section 1: Item 3 of 50
National Board of Medical Examiners®
Comprehensive Basic Science Self-Assessment
3. A 53-year-old man comes to the physician because of a 6-day history of
shortness of breath, cough, and pleuritic chest pain. His temperature is 38.9°C
(102°F), and respirations are 35/min. Sputum is purulent and rust colored.
Physical examination shows
decreased breath sounds, and crackles are heard at the left base. A Gram stain
of sputum shows gram-positive diplococci. A chest x-ray shows left-sided lobar
consolidation. Which of the following anatomic structures most likely allowed
rapid spread of
organisms between alveoli to involve the entire left lobe in this patient?
A) Alveolar capillaries
B) Germinal centers
C) Lymphatic capillaries
D) Pores of Kohn
E) Vascular sinusoids Answer - D.
The pores of Kohn form connections between alveoli and are present in normal
lung tissue. They are composed, at least in part, of type Il alveolar cells and
