NBME 30 – Complete Exam Review &
Explanations 2025!!
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 trANSWERportation 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 trANSWERcription 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 ANSWERwers: 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 ANSWERwers: 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 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.
Incorrect ANSWERwers: 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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Explanations 2025!!
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 trANSWERportation 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 trANSWERcription 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 ANSWERwers: 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 ANSWERwers: 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 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.
Incorrect ANSWERwers: 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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