First Aid USMLE STEP 1: Respiratory
Final Exam with Guaranteed Pass
Solutions 2025-2026 Updated.
How many periods does it take to develop the lung?
What are they? - Answer 5
1) Embryonic (weeks 4-7)
2) Pseudoglandular (weeks 5-16)
3) Canalicular (weeks 16-26)
4) Saccular (weeks 26-birth)
5) Alveolar (weeks 32-8 years)
Describe the embryonic stage - Answer Lung bud-> trachea-> mainstem bronchi-> secondary
(lobar) bronchi-> tertiary (segmental) bronchi
**Errors at this stage can lead to TE fistula
Describe the Pseudoglandular stage - Answer Endodermal tubules-> terminal bronchioles.
Surrounded by modest capillary network
**Respiration impossible, incompatible with life
Describe the Canalicular stage - Answer Terminal bronchioles-> respiratory bronchioles->
alveolar ducts.
Surrounded by prominent capillary network
,Terminal sacs separated by primary septae. Pneumocytes develop.
Describe the Alveolar stage - Answer Terminal sacs-> adult alveoli (d/t secondary septation).
In utero, "breathing" occurs via aspiration and expulsion of amniotic fluid-> increase in vascular
resistance through gestation. At birth, fluid gets replaced w/ air-> decrease in pulmonary
vascular resistance
**At birth: 20-70 million alveoli
**By 8 years: 300-400 million alveoli
What are the 2 congenital lung malformations & describe them - Answer 1) Pulmonary
hypoplasia= poorly developed bronchial tree w/ abnormal histology usually involving the right
lung. Associated w/ congenital diaphragmatic hernia, bilateral renal agenesis (Potter Syndrome)
2) Bronchogenic cysts= Caused by abnormal budding of foregut & dilation of terminal or large
bronchi. Discrete, round, sharply defined & air-filled densities on CXR. Drain poorly & cause
chronic infections.
What are Type I pneumocytes? - Answer thin squamous cells present in the alveoli,
functioning in optimal gas diffusion
Where are Type I pneumocytes found? - Answer 97% of alveolar surfaces. (line the alveoli)
Role & epithelium of Type I pneumocytes - Answer squamous. Thin for optimal gas diffusion
How is collapsing pressure calculated? - Answer P = (2 x surface tension) / radius
What is the function of Type II pneumocytes? - Answer secrete pulmonary surfactant -->
decrease alveolar surface tension; prevent alveolar collapse, decrease lung recoil & increase
compliance
What type of cells, histologically, are Type II pneumocytes? - Answer cuboidal
,When do Type II cells proliferate? - Answer in LUNG DAMAGE
What is the Law of Laplace? - Answer As the radius decreases upon expiration, alveoli have
an increased tendency to collapse.
What does "atelectasis" mean, and how is it caused? - Answer DEFINITION collapse of alveoli
CAUSES obstruction, compression, or contraction
--> damage to Type II pneumocytes --> loss of surfactant
NOTE Even reinflation may not return full function due to the loss of surfactant.
What is surfactant, chemically? - Answer a complex mix of lecithins, most importantly
DIPALMITOYLPHOSPHATIDYLCHOLINE
What are Clara (Club) cells? - Answer nonciliated, columnar cells with secretory granules
What do Clara cells secrete? - Answer a "watery" component of surfactant
What are the functions of Clara cells? - Answer to secrete a component of surfactant, to
degrade toxins, and to act as reserve cells
When does surfactant synthesis begin? - Answer around week 26 of gestation
When are mature levels of surfactant reached? - Answer around week 35 of gestation
If a child is born premature, is it likely that they will produce sufficient levels of surfactant? If
not, what is the child at risk of developing? - Answer no
atelectasis
What measurement indicates if a fetus has mature lung function? - Answer lecithin :
sphingomyelin above 2
This can be measured in the amniotic fluid.
, What lecithin:sphingomyelin ratio in amniotic fluid is predictive of neonatal RDS? - Answer
ratio <1.5
With what is neonatal RDS associated? - Answer prematurity: adequate surfactant levels are
not reached until week 35
C-section: d/t lack of release of stress-induced steroids (fetal glucocorticoids) --> no increased
synthesis of surfactant
maternal diabetes: increased fetal glucose-> increased fetal insulin-> decreased surfactant levels
What are the clinical features of neonatal RDS? - Answer increasing respiratory effort after
birth
tachypnea with use of accessory muscles
grunting
hypoxemia with cyanosis
CXR showing "ground-glass" appearance of lung
What are the complications of neonatal RDS? - Answer (1) persistently low O2 tension -->
hypoxemia --> increased risk of PDA, necrotizing enterocolitis
(2) Therapeutic supplemental oxygen--> increased risk of free radical injury (O2 can be toxic!) --
> "RIB"
R= Retinopathy of prematurity
I= Intraventricular hemorrhage
B= Bronchopulmonary dysplasia
What is the treatment for neonatal RDS? - Answer maternal steroids before birth;
artificial surfactant for infant
What is the order of structures in the Respiratory tree? - Answer Trachea-> bronchi->
bronchioles-> terminal bronchioles-> respiratory bronchioles-> alveolar sacs
What does smoking do the epithelial lining of the trachea? - Answer pseudo stratified
ciliated columnar-> squamous (via metaplasia & now sputum cannot be cleared)
Final Exam with Guaranteed Pass
Solutions 2025-2026 Updated.
How many periods does it take to develop the lung?
What are they? - Answer 5
1) Embryonic (weeks 4-7)
2) Pseudoglandular (weeks 5-16)
3) Canalicular (weeks 16-26)
4) Saccular (weeks 26-birth)
5) Alveolar (weeks 32-8 years)
Describe the embryonic stage - Answer Lung bud-> trachea-> mainstem bronchi-> secondary
(lobar) bronchi-> tertiary (segmental) bronchi
**Errors at this stage can lead to TE fistula
Describe the Pseudoglandular stage - Answer Endodermal tubules-> terminal bronchioles.
Surrounded by modest capillary network
**Respiration impossible, incompatible with life
Describe the Canalicular stage - Answer Terminal bronchioles-> respiratory bronchioles->
alveolar ducts.
Surrounded by prominent capillary network
,Terminal sacs separated by primary septae. Pneumocytes develop.
Describe the Alveolar stage - Answer Terminal sacs-> adult alveoli (d/t secondary septation).
In utero, "breathing" occurs via aspiration and expulsion of amniotic fluid-> increase in vascular
resistance through gestation. At birth, fluid gets replaced w/ air-> decrease in pulmonary
vascular resistance
**At birth: 20-70 million alveoli
**By 8 years: 300-400 million alveoli
What are the 2 congenital lung malformations & describe them - Answer 1) Pulmonary
hypoplasia= poorly developed bronchial tree w/ abnormal histology usually involving the right
lung. Associated w/ congenital diaphragmatic hernia, bilateral renal agenesis (Potter Syndrome)
2) Bronchogenic cysts= Caused by abnormal budding of foregut & dilation of terminal or large
bronchi. Discrete, round, sharply defined & air-filled densities on CXR. Drain poorly & cause
chronic infections.
What are Type I pneumocytes? - Answer thin squamous cells present in the alveoli,
functioning in optimal gas diffusion
Where are Type I pneumocytes found? - Answer 97% of alveolar surfaces. (line the alveoli)
Role & epithelium of Type I pneumocytes - Answer squamous. Thin for optimal gas diffusion
How is collapsing pressure calculated? - Answer P = (2 x surface tension) / radius
What is the function of Type II pneumocytes? - Answer secrete pulmonary surfactant -->
decrease alveolar surface tension; prevent alveolar collapse, decrease lung recoil & increase
compliance
What type of cells, histologically, are Type II pneumocytes? - Answer cuboidal
,When do Type II cells proliferate? - Answer in LUNG DAMAGE
What is the Law of Laplace? - Answer As the radius decreases upon expiration, alveoli have
an increased tendency to collapse.
What does "atelectasis" mean, and how is it caused? - Answer DEFINITION collapse of alveoli
CAUSES obstruction, compression, or contraction
--> damage to Type II pneumocytes --> loss of surfactant
NOTE Even reinflation may not return full function due to the loss of surfactant.
What is surfactant, chemically? - Answer a complex mix of lecithins, most importantly
DIPALMITOYLPHOSPHATIDYLCHOLINE
What are Clara (Club) cells? - Answer nonciliated, columnar cells with secretory granules
What do Clara cells secrete? - Answer a "watery" component of surfactant
What are the functions of Clara cells? - Answer to secrete a component of surfactant, to
degrade toxins, and to act as reserve cells
When does surfactant synthesis begin? - Answer around week 26 of gestation
When are mature levels of surfactant reached? - Answer around week 35 of gestation
If a child is born premature, is it likely that they will produce sufficient levels of surfactant? If
not, what is the child at risk of developing? - Answer no
atelectasis
What measurement indicates if a fetus has mature lung function? - Answer lecithin :
sphingomyelin above 2
This can be measured in the amniotic fluid.
, What lecithin:sphingomyelin ratio in amniotic fluid is predictive of neonatal RDS? - Answer
ratio <1.5
With what is neonatal RDS associated? - Answer prematurity: adequate surfactant levels are
not reached until week 35
C-section: d/t lack of release of stress-induced steroids (fetal glucocorticoids) --> no increased
synthesis of surfactant
maternal diabetes: increased fetal glucose-> increased fetal insulin-> decreased surfactant levels
What are the clinical features of neonatal RDS? - Answer increasing respiratory effort after
birth
tachypnea with use of accessory muscles
grunting
hypoxemia with cyanosis
CXR showing "ground-glass" appearance of lung
What are the complications of neonatal RDS? - Answer (1) persistently low O2 tension -->
hypoxemia --> increased risk of PDA, necrotizing enterocolitis
(2) Therapeutic supplemental oxygen--> increased risk of free radical injury (O2 can be toxic!) --
> "RIB"
R= Retinopathy of prematurity
I= Intraventricular hemorrhage
B= Bronchopulmonary dysplasia
What is the treatment for neonatal RDS? - Answer maternal steroids before birth;
artificial surfactant for infant
What is the order of structures in the Respiratory tree? - Answer Trachea-> bronchi->
bronchioles-> terminal bronchioles-> respiratory bronchioles-> alveolar sacs
What does smoking do the epithelial lining of the trachea? - Answer pseudo stratified
ciliated columnar-> squamous (via metaplasia & now sputum cannot be cleared)
