NBME 30 LATEST EXAM WITH COMPLETE
QUESTIONS AND CORRECT ANSWERS
RATED A+ WITH DETAILED RATIONALES
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 Correct
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 Correct 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.
QUESTIONS AND CORRECT ANSWERS
RATED A+ WITH DETAILED RATIONALES
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 Correct
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 Correct 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.
