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Respiratory system




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USMLE® Step 1 questions

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USMLE® Step 1 style questions USMLE

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A 17-year-old girl comes to the clinic for evaluation of a worsening productive cough. The symptoms have been worsening over the past week, and she has noticed increased production of foul-smelling, blood-tinged sputum. She has had multiple similar episodes in the past that mildly improved with antibiotics, but the cough has always persisted. The patient does not smoke cigarettes or use illicit substances. She takes pancreatic enzyme supplements for chronic diarrhea. Temperature is 39.0°C (102.2°F), pulse is 104/min, respirations are 22/min, and blood pressure is 124/75 mmHg. Physical examination reveals digital clubbing. Lung auscultation demonstrates diffuse wheezes and crackles. Which of the following findings will most likely be present in this patient?  

External References

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bronchiectasis p. 700


Aspergillus fumigatus p. , 150

cystic fibrosis p. 58

Kartagener syndrome p. 47, 714

Cystic fibrosis p. 58

bronchiectasis p. 700


Bronchiectasis can be broken down into “Bronchi” which refers to the bronchi and bronchiole airways of the lower lungs, and “-ectasis” means a dilation or expansion.

So in bronchiectasis chronic inflammation causes the bronchi and bronchioles to get damaged and dilated. Bronchiectasis is an obstructive lung disease, and that’s largely because the inflammation causes mucus plugs to form in the airways, and those mucus plugs obstruct airflow.

Normally, when taking a breath, the diaphragm muscle moves down and that creates negative pressure within the chest. This draws air in through the mouth or nose, and down the trachea.

Once there it goes into one of the primary bronchi or main bronchi, then secondary bronchi or lobar bronchus, then tertiary bronchi or segmental bronchus, and finally into the bronchioles which lead into the alveoli.

The alveoli is where the majority of gas exchange occurs in the lungs.

Taking a closer look at the airways, particularly the walls of the airways, they’ve got elastin fibers, which help give them their rubber-band like properties, and are lined with epithelial cells - some of which have brush-like projections, called cilia on their surface and others that secrete mucus.

The mucus traps foreign particles like bacteria and dust, and the mucus then gets swept upwards and out of the lungs by the cilia.

Together this whole system is called the mucociliary escalator.

Eventually that mucus and any stuck particles move into the esophagus and get swallowed and destroyed by the acid in the stomach! That’s right - you’re swallowing that mucus as you watch this.


Bronchiectasis is a chronic inflammation of the bronchi and the bronchioles, which damages the mucociliary escalator and the walls of the airways. This causes mucus to accumulate and get stuck in the airways, and form mucus plugs that can lead to serious infections, difficulty breathing, and a variety of other health problems. Common causes of bronchiectasis include long-term exposure to cigarette smoke, respiratory infections such as pneumonia, and cystic fibrosis.


  1. "Robbins Basic Pathology" Elsevier (2017)
  2. "Harrison's Principles of Internal Medicine, Twentieth Edition (Vol.1 & Vol.2)" McGraw-Hill Education / Medical (2018)
  3. "Pathophysiology of Disease: An Introduction to Clinical Medicine 7/E (ENHANCED EBOOK)" McGraw Hill Professional (2014)
  4. "CURRENT Medical Diagnosis and Treatment 2020" McGraw-Hill Education / Medical (2019)
  5. "Non–Cystic Fibrosis Bronchiectasis" American Journal of Respiratory and Critical Care Medicine (2013)
  6. "Etiology of Non–Cystic Fibrosis Bronchiectasis in Adults and Its Correlation to Disease Severity" Annals of the American Thoracic Society (2015)
  7. "Bronchiectasis" Nature Reviews Disease Primers (2018)

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