The tiny air sacs present in human lungs are called _______.

Correct Answer: A

Rationale: Alveoli are the tiny air sacs in the lungs, numbering about 500 million, where gas exchange occurs oxygen enters the blood, and carbon dioxide exits via diffusion across their thin walls. The bronchus (singular) and bronchioles are airways leading to alveoli, not sacs themselves bronchi branch from the trachea, and bronchioles are smaller terminal passages. 'All' is incorrect; only alveoli fit the description. Their vast surface area (about 100 m²) and capillary network make them the lungs' functional units, essential for oxygenation, a key focus in respiratory anatomy and diseases like emphysema, where alveoli degrade.

Correct Answer: A

Rationale: Yearly influenza (A), pneumonia vaccines (B), and adequate calories (D) aid COPD per GOLD guidelines, but A is primary (document lists 1). Flu shots cut exacerbations (30-50% risk drop). Pneumonia vaccine (PCV13) prevents S. pneumoniae. Limiting activity (C) worsens deconditioning exercise (e.g., 30 min/day) is key. Calories (e.g., 30 kcal/kg) combat cachexia from high metabolic demand (BMR +20%). A's emphasis reflects COPD's viral trigger risk flu doubles exacerbation odds, unlike C's harm or D's support role, making it the standout strategy.

Correct Answer: B

Rationale: Evaporation from oceans is the primary source of atmospheric water vapor, contributing ~86% of global input (~400,000 km³/year), due to oceans' vast surface (~71% of Earth) and solar-driven evaporation. Transpiration from plants adds ~10% (~50,000 km³/year), significant but secondary. Sublimation of ice is minor, limited by polar cold and area. Volcanic eruptions inject water vapor (~1% of total), but episodically. Oceans' dominance, per hydrologic cycle data (e.g., Trenberth), drives humidity, clouds, and precipitation, with ~90% of atmospheric vapor (1.3×10¹³ m³) cycling through evaporation, making it the key source, far exceeding terrestrial or geological inputs.

Correct Answer: C

Rationale: Gap junctions electrically connect cardiac muscle fibers, allowing rapid ion flow between cells via connexin channels, synchronizing contractions across the myocardium for a unified heartbeat. Desmosomes anchor fibers mechanically, not electrically. Tight junctions seal cells, rare in heart tissue. Interneurons are neural, not muscular. These gap junctions, within intercalated discs, enable the heart's autorhythmic, coordinated action, a key feature distinguishing cardiac from skeletal muscle, essential in physiology and arrhythmias where connectivity falters, disrupting rhythm.

Correct Answer: D

Rationale: A stab wound causing pneumothorax collapses the lung and expands the chest wall. Normally, negative intrapleural pressure (-5 cm H2O at FRC) holds lungs open against inward recoil. Air entry equalizes pressure to atmospheric (0 mmHg), collapsing the lung (300 mL residual volume remains). The chest wall, with outward elastic recoil, springs out, increasing thoracic diameter (Q41). A's dual expansion defies physics lungs can't inflate without negative pressure. B's FRC fixation ignores air's disruption (FRC ~2.5 L). C's dual collapse misreads chest mechanics. D's outcome lung deflation, chest expansion matches pneumothorax's loss of pleural seal, per physiology (Q58).

Correct Answer: C

Rationale: Initial AIHA treatment is corticosteroids (C e.g., prednisone 1 mg/kg), suppressing antibody production, raising Hb (e.g., >10 g/dL) in 70% of warm cases. Splenectomy (A) is second-line. Myelosuppressives (B) are later (e.g., rituximab). Plasma (D) is coagulopathy-related. None' denies. Steroids' rapid effect is key, guiding nursing for taper and side effect watch.

Correct Answer: C

Rationale: PCO2, or partial pressure of carbon dioxide, reflects the concentration of CO2 in blood, highest where metabolic waste accumulates and lowest where gas exchange removes it. The superior vena cava (SVC) carries deoxygenated blood from the upper body back to the heart, rich in CO2 from tissue metabolism, typically with a PCO2 of 45-46 mmHg, making it the highest among the options. Pulmonary veins carry oxygenated blood from the lungs to the heart after CO2 is offloaded in the alveoli, so their PCO2 is low (around 40 mmHg, arterial level). The midportion of pulmonary capillaries is where gas exchange occurs, transitioning from high venous PCO2 to lower arterial levels, averaging less than the SVC. Carotid bodies are chemoreceptors sensing blood gases, not a blood-containing structure, but even arterial blood they monitor has a PCO2 of about 40 mmHg. The SVC, as a major venous return vessel, consistently has the highest PCO2 due to its role in collecting metabolically produced CO2 before pulmonary gas exchange, distinguishing it from the other options.

Correct Answer: C

Rationale: During heart transplants, vagus nerves (parasympathetic) are severed, losing their slowing effect on the SA node, raising resting heart rate to ~100 bpm its intrinsic pace. Glossopharyngeal nerves sense pressure, not rate directly. Cardiac accelerator (sympathetic) nerves speed rate, intact or regrown later. Phrenic nerves drive diaphragm, not heart. This denervation removes 'brake,' key in post-transplant care, explaining tachycardia and need for rate control.

Correct Answer: A

Rationale: The nurse asks if the 6-month-old has trouble breathing to gauge acuity, as respiratory distress (e.g., rapid breathing, grunting) in infants signals severe flu complications like bronchiolitis, needing urgent care. Small airways and immature immunity make this critical too young for flu shots, they're at high risk. Fever matters, but alone doesn't define urgency. Nasal drainage is typical, not acute. Symptom onset aids context, not immediate severity. Prioritizing breathing aligns with pediatric triage, ensuring the parent seeks help if this red flag appears, protecting the infant from rapid deterioration common in flu-related respiratory crises.