NBME 30
1. 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: 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.
, NBME 30
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. 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: 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.
, NBME 30
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. 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: 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 allow for the
passage of air, fluid, phagocytes, and in the setting of pneumonia, bacteria between
adjacent alveoli. By allowing equilibration between adjacent alveoli, the pores of
Kohn aid in normal oxygenation and in the prevention of atelectasis. However,
infectious organisms and inflammation may also spread between adjacent alveoli
through these apertures.
, NBME 30
Incorrect Answers: A, B, C, and E.
Alveolar capillaries (Choice A) surround each alveolus and are crucial for gas
exchange. However, they do not provide a direct connection between adjacent
alveoli, provided that the alveolar and capillary endothelia remain intact.
Germinal centers (Choice B) allow for the development of B lymphocytes and are
important in mounting an adaptive immune response to pulmonary pathogens. They
do not form connections between alveoli.
Lymphatic capillaries (Choice C) allow for the drainage of interstitial fluid from the
lung parenchyma to the lymphatic ducts and eventually to the heart. These
passages do not form direct anastomoses between adjacent alveoli.
Vascular sinusoids (Choice E) are present in hepatic tissue and create
anastomoses between the portal and systemic circulation, allowing for the
exchange of nutrients with hepatocytes. They are not present in pulmonary tissue.
Educational Objective: The pores of Kohn form connections between alveoli and
are present in normal lung tissue. They allow for the passage of air, fluid,
phagocytes, and, in the setting of pneumonia, bacteria between adjacent alveoli.
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4. 4
Exam Section 1: Item 4 of 50
National Board of Medical Examiners®
Comprehensive Basic Science Self-Assessment
4. A female newborn is born at 39 weeks' gestation following an uneventful
pregnancy. The Apgar scores are 10 at 1 and 5 minutes, respectively. The
newborn is at the 50th percentile for length and 25th percentile for weight.
She has normal morphologic
features. The parents are told she has an enzyme defect that, if left untreated,
will result in failure to attain early developmental milestones, microcephaly,
hyperactivity, seizures, intellectual disability, and a mousy odor of the skin
1. 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: 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.
, NBME 30
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. 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: 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.
, NBME 30
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. 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: 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 allow for the
passage of air, fluid, phagocytes, and in the setting of pneumonia, bacteria between
adjacent alveoli. By allowing equilibration between adjacent alveoli, the pores of
Kohn aid in normal oxygenation and in the prevention of atelectasis. However,
infectious organisms and inflammation may also spread between adjacent alveoli
through these apertures.
, NBME 30
Incorrect Answers: A, B, C, and E.
Alveolar capillaries (Choice A) surround each alveolus and are crucial for gas
exchange. However, they do not provide a direct connection between adjacent
alveoli, provided that the alveolar and capillary endothelia remain intact.
Germinal centers (Choice B) allow for the development of B lymphocytes and are
important in mounting an adaptive immune response to pulmonary pathogens. They
do not form connections between alveoli.
Lymphatic capillaries (Choice C) allow for the drainage of interstitial fluid from the
lung parenchyma to the lymphatic ducts and eventually to the heart. These
passages do not form direct anastomoses between adjacent alveoli.
Vascular sinusoids (Choice E) are present in hepatic tissue and create
anastomoses between the portal and systemic circulation, allowing for the
exchange of nutrients with hepatocytes. They are not present in pulmonary tissue.
Educational Objective: The pores of Kohn form connections between alveoli and
are present in normal lung tissue. They allow for the passage of air, fluid,
phagocytes, and, in the setting of pneumonia, bacteria between adjacent alveoli.
%3D
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4. 4
Exam Section 1: Item 4 of 50
National Board of Medical Examiners®
Comprehensive Basic Science Self-Assessment
4. A female newborn is born at 39 weeks' gestation following an uneventful
pregnancy. The Apgar scores are 10 at 1 and 5 minutes, respectively. The
newborn is at the 50th percentile for length and 25th percentile for weight.
She has normal morphologic
features. The parents are told she has an enzyme defect that, if left untreated,
will result in failure to attain early developmental milestones, microcephaly,
hyperactivity, seizures, intellectual disability, and a mousy odor of the skin
