General Physiology (Pulmonology)

Question 1

What are the predominate cells within the lung?

Answer 1

• Type I pneumocytes. These cells are primarily responsible for gas diffusion in the respiratory portion of the lungs. These cells are unable to replicate.
• Type Il pneumocytes. These cells synthesize lecithin, which refers to a class of fatty substances used to produce lung surfactant. Lecithin is stored as lamellar bodies in the cytoplasm, giving the cells their foamy appearance. When released, these amphipathic molecules decrease the surface tension in alveoli and increase lung compliance, thus facilitating breathing. These cells can replicate and produce either new type II pneumocytes or type I pneumocytes. Following injury Type II pneumocytes will replicate, and take on a foamy-appearing cell after lung injury.
• Alveolar macrophages are a major source of cytokine release in the lower lung. Macrophages also take on a foamy appearance through the accumulation of digested fats that the cells scavenge. However, alveolar macrophages are large and pleomorphic with large eccentric nuclei.
• Club cells are responsible for toxin degradation in the lower lung. These are cuboidal, non-ciliated cells that are present in the terminal bronchioles of lungs. Club cells can not produce of types I and Il pneumocytes and do not form clusters of cuboidal, foamy-appearing cells after lung injury.
• Goblet cells are tall, simple columnar cells that produce mucus in the lungs. These cells contain mucin granules that stain positive for PAS and line the respiratory tract until the terminal bronchioles.

Question 2

Which cell type is the most numerous?

Answer 2

Type I pneumocytes. Type I pneumocytes are squamous cells that comprise > 95% of the alveolar surface.

Question 3

When do the lungs stop developing?

Answer 3

There are 20-70 million alveoli at birth and approx. 300 million alveoli in a healthy adult. Between 36 weeks’ gestation and 8 years of age, alveoli continue to increase in number (but not in size) through the formation of secondary alveolar septa. This process, also known as the alveolar stage, marks the final stage of lung development. Prior to this stage, the lungs and airways undergo four stages of development: the embryonic stage (weeks 4-7), pseudoglandular stage (weeks 5-17), canalicular stage (weeks 16-25), and saccular stage, in which primary alveolar septa form (from 26 weeks’ gestation to birth).

Question 4

What size of particle are cleared by the mucociliary escalator

Answer 4

Particles that range from 3-10 um in size are most likely to deposit in the trachea and/or the bronchi, which are lined by a pseudostratified epithelium. These particles are then trapped in mucus secreted by goblet cells and subsequently pushed upward toward the nasopharyngeal cavity by the action of the ciliated epithelium of the respiratory tract, i.e., the mucociliary escalator.

Question 5

What is the span for the superior vs inferior lobes?

Answer 5

Answer 6

Question 7

What is assessed with spirometry?

Answer 7

Lung volumes, lung capacities, ratios.

Question 8

What is the Aa gradient and how can this help understand the underlying etiology of hypoxia?

Answer 8

Difference in oxygen between the alveoli and arteriole.

Question 9

What are the physiological changes that occur in the lung with age?

Answer 9

Decreased FEV1

Question 10

How does the V/Q ratio change with pathologies?

Answer 10

Intrapulmonary shunting causes perfusion without ventilation (V=0)

Deadspace causes ventilation without perfusion (Q=0)