Elastic recoil of lung tissue US Medical PG Practice Questions and MCQs
Practice US Medical PG questions for Elastic recoil of lung tissue. These multiple choice questions (MCQs) cover important concepts and help you prepare for your exams.
Elastic recoil of lung tissue US Medical PG Question 1: During a clinical study examining the diffusion of gas between the alveolar compartment and the pulmonary capillary blood, men between the ages of 20 and 50 years are evaluated while they hold a sitting position. After inhaling a water-soluble gas that rapidly combines with hemoglobin, the concentration of the gas in the participant's exhaled air is measured and the diffusion capacity is calculated. Assuming that the concentration of the inhaled gas remains the same, which of the following is most likely to increase the flow of the gas across the alveolar membrane?
- A. Deep exhalation
- B. Entering a cold chamber
- C. Treadmill exercise (Correct Answer)
- D. Standing straight
- E. Assuming a hunched position
Elastic recoil of lung tissue Explanation: ***Correct: Treadmill exercise***
- **Treadmill exercise** increases cardiac output and pulmonary blood flow, which in turn recruits and distends more **pulmonary capillaries**. This increases the **surface area** available for gas exchange and reduces the diffusion distance, thereby enhancing the flow of gas across the alveolar membrane.
- Exercise also typically leads to deeper and more frequent breaths, increasing the **ventilation-perfusion matching** and overall efficiency of gas exchange.
- According to Fick's law of diffusion (Vgas = A/T × D × ΔP), increasing the surface area (A) directly increases gas flow.
*Incorrect: Deep exhalation*
- **Deep exhalation** would empty the lungs more completely, potentially leading to alveolar collapse in some regions and thus **decreasing the alveolar surface area** available for gas exchange.
- This would also reduce the **driving pressure** for gas diffusion by lowering the alveolar concentration of the inhaled gas.
*Incorrect: Entering a cold chamber*
- Exposure to a **cold chamber** can cause **bronchoconstriction** in some individuals, particularly those with reactive airways, which would increase airway resistance and potentially reduce alveolar ventilation.
- While metabolic rate may slightly increase in the cold, the primary effect on the lungs is unlikely to promote increased gas diffusion in a healthy individual.
*Incorrect: Standing straight*
- **Standing straight** is a normal physiological posture and does not significantly alter the **pulmonary capillary recruitment** or the alveolar surface area in a way that would dramatically increase gas flow compared to a seated position.
- There might be minor gravitational effects on blood flow distribution, but these are generally less impactful than dynamic changes like exercise.
*Incorrect: Assuming a hunched position*
- **Assuming a hunched position** can restrict chest wall expansion and diaphragm movement, leading to **reduced tidal volume** and overall alveolar ventilation.
- This posture, by reducing lung volumes and potentially compressing the lungs, would likely **decrease the effective surface area** for gas exchange and therefore reduce gas flow.
Elastic recoil of lung tissue US Medical PG Question 2: A 63-year-old man with alpha-1-antitrypsin deficiency is brought to the emergency department 1 hour after his daughter found him unresponsive. Despite appropriate care, the patient dies. At autopsy, examination of the lungs shows enlargement of the airspaces in the respiratory bronchioles and alveoli. Enzymatic activity of which of the following cells is the most likely cause of these findings?
- A. Alveolar macrophages (Correct Answer)
- B. Ciliated bronchiolar epithelial cells
- C. Elastic fibers in alveolar septa
- D. Type I pneumocytes
- E. Alveolar septal cells
Elastic recoil of lung tissue Explanation: ***Alveolar macrophages***
- In **alpha-1-antitrypsin deficiency**, alveolar macrophages (and neutrophils) release **elastase**, which is normally inhibited by alpha-1-antitrypsin.
- Unchecked elastase activity from alveolar macrophages leads to the **destruction of elastic fibers** in the alveolar walls, causing emphysema with characteristic **panacinar** distribution (worse in lower lobes).
- This results in enlargement of airspaces distal to terminal bronchioles.
*Ciliated bronchiolar epithelial cells*
- These cells are primarily involved in **mucociliary clearance** and do not produce proteolytic enzymes that degrade elastic tissue.
- Their dysfunction would lead to impaired mucus clearance and increased susceptibility to infections, but not emphysema.
*Elastic fibers in alveolar septa*
- Elastic fibers are **extracellular matrix components**, not cells.
- While their destruction is the pathological mechanism of emphysema, they do not have enzymatic activity.
*Type I pneumocytes*
- **Type I pneumocytes** form the structural lining of the alveoli and are primarily involved in gas exchange.
- They do not produce elastase or other proteolytic enzymes responsible for tissue destruction in emphysema.
*Alveolar septal cells*
- This term broadly refers to structural cells including Type I and Type II pneumocytes.
- While these cells may be damaged secondarily in emphysema, they do not produce the elastase responsible for elastic fiber destruction.
Elastic recoil of lung tissue US Medical PG Question 3: Which of the following physiologic changes decreases pulmonary vascular resistance (PVR)?
- A. Inhaling the inspiratory reserve volume (IRV)
- B. Exhaling the entire vital capacity (VC)
- C. Exhaling the expiratory reserve volume (ERV)
- D. Breath holding maneuver at functional residual capacity (FRC)
- E. Inhaling the entire vital capacity (VC) (Correct Answer)
Elastic recoil of lung tissue Explanation: ***Inhaling the entire vital capacity (VC)***
- As lung volume increases from FRC to TLC (which includes inhaling the entire VC), alveolar vessels are **stretched open**, and extra-alveolar vessels are **pulled open** by the increased radial traction, leading to a decrease in PVR.
- This **maximizes the cross-sectional area** of the pulmonary vascular bed, lowering resistance.
*Inhaling the inspiratory reserve volume (IRV)*
- While inhaling IRV increases lung volume, it's not the maximal inspiration of the entire VC where **PVR is typically at its lowest**.
- PVR continues to decrease as lung volume approaches total lung capacity (TLC).
*Exhaling the entire vital capacity (VC)*
- Exhaling the entire vital capacity leads to very low lung volumes, where PVR significantly **increases**.
- At low lung volumes, **alveolar vessels become compressed** and extra-alveolar vessels **narrow**, increasing resistance.
*Exhaling the expiratory reserve volume (ERV)*
- Exhaling the ERV results in a lung volume below FRC, which causes a **marked increase in PVR**.
- This is due to the **compression of alveolar vessels** and decreased radial traction on extra-alveolar vessels.
*Breath holding maneuver at functional residual capacity (FRC)*
- At FRC, the PVR is at an **intermediate level**, not its lowest.
- This is the point where the opposing forces affecting alveolar and extra-alveolar vessels are somewhat balanced, but not optimized for minimal resistance.
Elastic recoil of lung tissue US Medical PG Question 4: A 55-year-old woman comes to the physician with a 6-month history of cough and dyspnea. She has smoked 1 pack of cigarettes daily for the past 30 years. Analysis of the sputum sample from bronchoalveolar lavage shows abnormal amounts of an isoform of elastase that is normally inhibited by alpha-1 antitrypsin. The cell responsible for secreting this elastase is most likely also responsible for which of the following functions?
- A. Phagocytosis of foreign material (Correct Answer)
- B. Production of lactoferrin
- C. Degradation of toxins
- D. Secretion of mucus
- E. Diffusion of gases
Elastic recoil of lung tissue Explanation: ***Phagocytosis of foreign material***
- The abnormal elastase described is **neutrophil elastase**, which is normally inhibited by **alpha-1 antitrypsin**.
- **Neutrophils** are the primary cells responsible for secreting this elastase, and their main function is the **phagocytosis of foreign material** and pathogens.
*Production of lactoferrin*
- **Lactoferrin** is an iron-binding protein with antimicrobial properties, primarily produced by **neutrophils**, but it is not their defining or most unique function in the context of elastase secretion and lung pathology.
- While neutrophils do produce lactoferrin, the question asks for a function that aligns with the described cellular pathology following elastase release.
*Degradation of toxins*
- While certain immune cells and organs (e.g., liver) are involved in **detoxification**, it is not a primary or most characteristic function of **neutrophils** in the lung.
- Neutrophils are more focused on direct microbial killing and inflammation rather than broad toxin degradation.
*Secretion of mucus*
- **Mucus secretion** in the airways is primarily a function of **goblet cells** and submucosal glands, not neutrophils.
- Excessive mucus secretion is a feature of chronic bronchitis, which can coexist with emphysema, but neutrophils themselves do not secrete mucus.
*Diffusion of gases*
- **Gas diffusion** is the primary function of **type I pneumocytes** in the alveolar sacs, which form the thin barrier between air and blood.
- This function is entirely unrelated to the role of neutrophils or the secretion of elastase.
Elastic recoil of lung tissue US Medical PG Question 5: A 57-year-old man comes to the physician because of a 2-year history of fatigue, worsening shortness of breath, and a productive cough for 2 years. He has smoked 1 pack of cigarettes daily for the past 40 years. Examination shows pursed-lip breathing and an increased anteroposterior chest diameter. There is diffuse wheezing bilaterally and breath sounds are distant. Which of the following parameters is most likely to be decreased in this patient?
- A. Thickness of small airways
- B. Work of breathing
- C. Lung elastic recoil (Correct Answer)
- D. Lower airway resistance
- E. Pulmonary vascular pressure
Elastic recoil of lung tissue Explanation: ***Lung elastic recoil***
- The patient's presentation (long smoking history, dyspnea, pursed-lip breathing, increased AP diameter, distant breath sounds, and wheezing) is classic for **emphysema**, a form of **COPD**.
- Emphysema involves the destruction of **alveolar walls** and **elastic fibers**, leading to a significant decrease in the lung's ability to passively recoil during expiration.
*Thickness of small airways*
- In COPD, particularly chronic bronchitis, there is often **inflammation and thickening of the small airways** due to goblet cell hyperplasia and mucus gland hypertrophy, increasing their thickness, not decreasing it.
- This thickening contributes to increased airway resistance.
*Work of breathing*
- The **destruction of elastic recoil** in emphysema means the patient must actively use accessory muscles to exhale, significantly **increasing the work of breathing**, which is evident from pursed-lip breathing.
- Patients with COPD expend much more energy to breathe than healthy individuals.
*Lower airway resistance*
- Emphysema, while characterized by alveolar destruction, also has an obstructive component due to **airway collapse during expiration** (loss of radial traction) and potential inflammation/mucus, which leads to **increased lower airway resistance**, not decreased resistance.
- This increased resistance contributes to air trapping and wheezing.
*Pulmonary vascular pressure*
- Chronic hypoxia resulting from severe COPD can lead to **pulmonary vasoconstriction** and remodeling of the pulmonary arteries, causing **pulmonary hypertension** and an increase in pulmonary vascular pressure.
- This is a common complication in advanced COPD, not a decreased parameter.
Elastic recoil of lung tissue US Medical PG Question 6: In which of the following pathological states would the oxygen content of the trachea resemble the oxygen content in the affected alveoli?
- A. Emphysema
- B. Exercise
- C. Pulmonary embolism (Correct Answer)
- D. Pulmonary fibrosis
- E. Foreign body obstruction distal to the trachea
Elastic recoil of lung tissue Explanation: ***Pulmonary embolism***
- A pulmonary embolism blocks **blood flow** to a portion of the lung, creating **dead space ventilation** (high V/Q ratio).
- In the affected alveoli, **no blood perfusion** means no oxygen extraction occurs, so the alveolar oxygen content remains **high and similar to tracheal/inspired air**.
- This is the classic physiological state where ventilation continues but perfusion is absent, preventing gas exchange.
*Foreign body obstruction distal to the trachea*
- A complete obstruction **prevents fresh air** from reaching the affected alveoli.
- The trapped gas undergoes **resorption atelectasis**: oxygen is absorbed into capillary blood, CO2 diffuses in, and alveolar gas equilibrates with **venous blood** composition.
- Alveolar oxygen content becomes **very low**, not similar to tracheal air.
*Emphysema*
- Emphysema involves destruction of **alveolar walls** and enlargement of airspaces with impaired gas exchange.
- While V/Q mismatch occurs, oxygen is still extracted by perfusing blood.
- Alveolar oxygen content is **lower than tracheal air** due to ongoing (though inefficient) gas exchange.
*Exercise*
- During exercise, **oxygen consumption increases** dramatically with enhanced cardiac output and oxygen extraction.
- Alveolar oxygen content is **significantly lower** than tracheal air due to increased oxygen uptake by blood.
*Pulmonary fibrosis*
- Pulmonary fibrosis causes **thickening of the alveolar-capillary membrane**, impairing oxygen diffusion.
- Despite diffusion limitation, blood still perfuses the alveoli and extracts oxygen.
- Alveolar oxygen content is **lower than tracheal air**, though the A-a gradient is increased.
Elastic recoil of lung tissue US Medical PG Question 7: An 8-year old boy is brought into clinic for evaluation of possible scoliosis that was newly found on a routine exam at school. On exam, he is also noted to be in the 99th percentile for height and 70th percentile for weight. He appears to have abnormally long extremities as well as an upward lens dislocation on ophthalmologic exam. A mutation leading to a defect in which of the following proteins is the most likely cause of his condition?
- A. Type IV collagen
- B. Type I collagen
- C. Elastin
- D. Fibrillin (Correct Answer)
- E. ATP7A
Elastic recoil of lung tissue Explanation: ***Fibrillin***
- The patient's clinical features, including **scoliosis**, being in the **99th percentile for height**, having **abnormally long extremities** (arachnodactyly), and **upward lens dislocation**, are classic signs of **Marfan syndrome**.
- **Marfan syndrome** is an autosomal dominant disorder caused by a mutation in the *FBN1* gene, which codes for **fibrillin-1**, a glycoprotein essential for the formation of elastic fibers in connective tissue.
*Type I collagen*
- Defects in **Type I collagen** are primarily associated with **osteogenesis imperfecta**, characterized by **bone fragility**, multiple fractures, blue sclera, and hearing loss.
- While it can present with skeletal abnormalities, it does not typically cause the extreme height, arachnodactyly, or lens dislocation seen in this patient.
*Type IV collagen*
- Defects in **Type IV collagen** are linked to conditions like **Alport syndrome**, which primarily affects the kidneys (glomerulonephritis), ears (hearing loss), and eyes (ocular defects including lenticonus), but not typically the skeletal features described.
- It is a major component of **basement membranes**, important for filtration and structural support in various organs.
*Elastin*
- Mutations in **elastin** are associated with conditions like **supravalvular aortic stenosis** (Williams syndrome) or cutis laxa, which affect the skin and cardiovascular system.
- It does not explain the characteristic skeletal and ocular findings of Marfan syndrome.
*ATP7A*
- A mutation in the *ATP7A* gene, which codes for an ATPase involved in copper transport, is responsible for **Menkes disease**.
- **Menkes disease** is characterized by **sparse, kinky hair**, failure to thrive, neurological degeneration, and connective tissue abnormalities due to copper deficiency, which does not align with the patient's presentation.
Elastic recoil of lung tissue US Medical PG Question 8: Which of the following factors gives the elastin molecule the ability to stretch and recoil?
- A. Elastase activity
- B. Triple helix formation
- C. Cross-links between lysine residues (Correct Answer)
- D. Cleavage of disulfide rich terminal regions
- E. Hydroxylation of proline and lysine rich regions
Elastic recoil of lung tissue Explanation: ***Cross-links between lysine residues***
- The extensive **crosslinking** between **lysine residues** in elastin forms a rubber-like network that allows the molecule to stretch under tension and recoil to its original shape.
- These cross-links are formed by specialized amino acids, such as **desmosin** and **isodesmosin**, derived from multiple lysine residues, creating a stable yet flexible structure.
*Elastase activity*
- **Elastase** is an enzyme that **degrades elastin**, breaking down its structure rather than contributing to its elastic properties.
- Increased elastase activity can lead to conditions like **emphysema**, where the loss of elastin's elasticity impairs lung function.
*Triple helix formation*
- **Triple helix formation** is characteristic of **collagen**, providing it with tensile strength and rigidity, rather than the stretch and recoil properties of elastin.
- Elastin's structure is largely amorphous, allowing for greater flexibility compared to collagen's rigid helical organization.
*Cleavage of disulfide rich terminal regions*
- While some proteins utilize **disulfide bonds** for structural integrity, **elastin's elasticity** is primarily due to its cross-linked lysine network, not disulfide bond cleavage.
- The formation or cleavage of disulfide bonds is not the primary mechanism by which elastin exerts its characteristic stretch and recoil.
*Hydroxylation of proline and lysine rich regions*
- **Hydroxylation of proline and lysine residues** is a crucial post-translational modification for **collagen stability** (e.g., in vitamin C deficiency leading to scurvy) but is not a defining feature of elastin's elasticity.
- Elastin contains fewer hydroxyproline residues and no hydroxylysine, distinguishing it from collagen's structure and function.
Elastic recoil of lung tissue US Medical PG Question 9: A 55-year-old man with a 60 pack-year smoking history is referred by his primary care physician for a pulmonary function test (PFT). A previously obtained chest x-ray is shown below. Which of the following will most likely appear in his PFT report?
- A. Residual volume increased, total lung capacity decreased
- B. Residual volume normal, total lung capacity decreased
- C. Residual volume normal, total lung capacity normal
- D. Residual volume decreased, total lung capacity increased
- E. Residual volume increased, total lung capacity increased (Correct Answer)
Elastic recoil of lung tissue Explanation: ***Residual volume increased, total lung capacity increased***
- The chest X-ray shows **hyperinflation** and a **flattened diaphragm**, which are classic signs of **emphysema**, a type of COPD.
- In emphysema, destruction of alveolar walls leads to air trapping, resulting in an **increased residual volume** and **total lung capacity**.
*Residual volume increased, total lung capacity decreased*
- An increased residual volume suggests **air trapping**, typical of obstructive lung diseases like emphysema.
- However, a **decreased total lung capacity** is characteristic of restrictive lung diseases, which would contradict the clinical and radiological findings for emphysema.
*Residual volume normal, total lung capacity decreased*
- A **normal residual volume** indicates no significant air trapping, which is inconsistent with emphysema.
- A **decreased total lung capacity** is seen in restrictive lung diseases, not obstructive diseases like emphysema.
*Residual volume normal, total lung capacity normal*
- **Normal lung volumes** would indicate healthy lung function, which is not expected in a patient with a heavy smoking history and radiological evidence of emphysema.
- The patient's 60 pack-year smoking history strongly points towards significant lung pathology.
*Residual volume decreased, total lung capacity increased*
- A **decreased residual volume** would suggest improved exhalation and less air trapping, which is contrary to the pathophysiology of emphysema.
- While total lung capacity can be increased in emphysema, the decrease in residual volume makes this option incorrect.
Elastic recoil of lung tissue US Medical PG Question 10: A 64-year-old man presents to his primary care physician for follow-up of a severe, unrelenting, productive cough of 2 years duration. The medical history includes type 2 diabetes mellitus, which is well-controlled with insulin. He has a 25-pack-year smoking history and is an active smoker. The blood pressure is 135/88 mm Hg, the pulse is 94/min, the temperature is 36.9°C (98.5°F), and the respiratory rate is 18/min. Bilateral wheezes and crackles are heard on auscultation. A chest X-ray reveals cardiomegaly, increased lung markings, and a flattened diaphragm. Which of the following is most likely in this patient?
- A. Increased pH of the arterial blood
- B. Increased cerebral vascular resistance
- C. Increased pulmonary arterial resistance (Correct Answer)
- D. Decreased carbon dioxide content of the arterial blood
- E. Increased right ventricle compliance
Elastic recoil of lung tissue Explanation: ***Increased pulmonary arterial resistance***
- This patient's long-standing **smoking history**, chronic productive cough, **wheezes**, and **crackles** suggest **Chronic Obstructive Pulmonary Disease (COPD)**, likely including chronic bronchitis and emphysema.
- **COPD** often leads to **hypoxia**, causing **pulmonary vasoconstriction** and subsequent increase in **pulmonary arterial resistance**, eventually leading to **pulmonary hypertension** and **cor pulmonale** (right-sided heart failure).
*Increased pH of the arterial blood*
- Patients with severe COPD and chronic respiratory insufficiency often develop **chronic hypercapnia** (increased **PaCO2**), leading to **respiratory acidosis** and a tendency towards a **decreased pH** or a normal pH with compensation.
- An **increased pH** (alkalosis) would be less likely in the context of chronic ventilatory compromise.
*Increased cerebral vascular resistance*
- In chronic hypercapnia and hypoxia, **cerebral blood vessels** typically **dilate** to maintain cerebral perfusion, leading to **decreased cerebral vascular resistance**, not increased.
- This vasodilation can contribute to symptoms like headaches and altered mental status in severe cases.
*Decreased carbon dioxide content of the arterial blood*
- Patients with chronic obstructive lung disease often have impaired gas exchange, leading to **CO2 retention** (**hypercapnia**).
- Therefore, the **arterial carbon dioxide content** would typically be **increased**, not decreased.
*Increased right ventricle compliance*
- In the setting of chronic **pulmonary hypertension**, the right ventricle is subjected to increased pressure overload, leading to **ventricular hypertrophy** and eventually **decreased compliance** and **ventricular dysfunction**.
- **Increased compliance** (meaning the ventricle stretches more easily) is contrary to the expected response in chronic pressure overload.
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