Pneumococcal vaccines (PCV13/PCV20 or PPSV23) reduce the risk of invasive pneumococcal disease including pneumonia, especially in elderly and high-risk patients.

Tension pneumothorax is a medical emergency treated with immediate needle decompression (2nd intercostal space, midclavicular line) followed by chest tube placement.

Inhaled corticosteroids reduce chronic airway inflammation and are used for long-term asthma control, not acute rescue.

Tissue biopsy and histopathology remain the gold standard for confirming lung cancer diagnosis and subtype.

CT pulmonary angiography is the current gold-standard imaging test for diagnosing pulmonary embolism in most clinical settings.

Pulse oximetry estimates the percentage of hemoglobin saturated with oxygen (SpO2), a surrogate for arterial oxygenation.

In chronic CO2 retainers, a controlled target SpO2 of 88-92% avoids suppressing hypoxic respiratory drive and worsening hypercapnia.

A peak flow meter provides a simple, portable measure of PEFR for home monitoring of asthma control.

The standard intensive-phase regimen (RIPE) is Rifampin, Isoniazid, Pyrazinamide, and Ethambutol.

Short-acting beta-2 agonists like salbutamol provide rapid bronchodilation and are first-line for acute asthma symptom relief.

Coal workers' pneumoconiosis results from chronic inhalation of coal dust, leading to characteristic pigment-laden macrophages and nodules.

Silicosis characteristically causes nodular fibrosis predominantly in the upper lobes.

Asbestos exposure is strongly associated with malignant mesothelioma of the pleura, as well as increased bronchogenic carcinoma risk.

Sarcoidosis is a systemic disease characterized by non-caseating granulomas, commonly affecting the lungs and hilar lymph nodes.

Primary spontaneous pneumothorax typically occurs in tall, thin young males from rupture of apical subpleural blebs.

Apical tumors can invade the sympathetic chain/stellate ganglion, producing Horner syndrome (ptosis, miosis, anhidrosis).

Squamous cell carcinoma of the lung is the classic cause of paraneoplastic hypercalcemia via PTHrP secretion.

Small cell lung carcinoma, of neuroendocrine origin, is the classic cause of paraneoplastic ectopic ACTH secretion.

Squamous cell carcinoma classically arises centrally, is strongly linked to smoking, and can cavitate.

Adenocarcinoma is now the most common type of lung cancer overall, often arising peripherally, including in non-smokers.

ARDS is histologically characterized by diffuse alveolar damage and formation of hyaline membranes lining alveolar walls.

The classic (though not always present) triad of PE is sudden dyspnea, pleuritic chest pain, and hemoptysis.

The majority of pulmonary emboli originate from deep vein thrombi in the lower extremities, especially the proximal veins.

The Ghon complex refers to the combination of the primary parenchymal (Ghon) lesion and associated hilar lymphadenopathy.

Caseous ("cheese-like") necrosis is the hallmark of tuberculous granulomas.

Mycoplasma pneumoniae is a common cause of atypical pneumonia, especially in younger patients, with an interstitial (not lobar) pattern.

Classic lobar pneumonia progresses through congestion, red hepatization, gray hepatization, and resolution.

Streptococcus pneumoniae remains the most common cause of typical community-acquired pneumonia.

Bronchiectasis involves permanent dilation of bronchi/bronchioles from chronic inflammation and destruction of the muscular and elastic wall components.

Curschmann spirals (mucus plugs) and Charcot-Leyden crystals (from eosinophil breakdown) are classic asthma findings, along with smooth muscle hypertrophy.

An elevated Reid index (gland layer thickness/total bronchial wall thickness) reflects mucous gland hyperplasia seen in chronic bronchitis.

Chronic bronchitis is a clinical diagnosis defined by productive cough for at least 3 months in 2 consecutive years.

Centriacinar emphysema, related to smoking, primarily affects the upper lobes and central portions of the acinus.

Alpha-1 antitrypsin deficiency causes panacinar emphysema, typically affecting the lower lobes, due to unopposed elastase activity.

Cigarette smoking is by far the most common and important cause of COPD.

Normal PaO2 in a healthy adult breathing room air at sea level is approximately 95-100 mmHg.

Due to gravity's effect on perfusion, the apex has relatively higher V/Q (>1) while the base has lower V/Q (<1) despite higher absolute ventilation and perfusion at the base.

Stretch receptors in airway smooth muscle trigger this reflex, terminating inspiration to prevent excessive lung distension.

Peripheral chemoreceptors primarily detect significant hypoxemia, becoming important in conditions like chronic CO2 retention (COPD) where hypoxic drive predominates.

Central chemoreceptors in the medulla sense changes in CSF pH, reflecting arterial CO2 levels, and are the primary drivers of minute-to-minute ventilation control.

The dorsal and ventral respiratory groups in the medulla generate the basic rhythm of breathing, modulated by pontine centers.

Carbonic anhydrase rapidly catalyzes the hydration of CO2 to carbonic acid, which dissociates into bicarbonate and H+.

Approximately 70% of CO2 is transported as bicarbonate (HCO3-), formed via carbonic anhydrase in red blood cells.

The Haldane effect: oxygenated hemoglobin has reduced affinity for CO2 and H+, promoting CO2 unloading at the lungs.

The Bohr effect describes how rising CO2 and H+ in metabolically active tissue reduce hemoglobin's O2 affinity, favoring oxygen delivery.

Increased pH (alkalosis) shifts the curve LEFT (increased O2 affinity); the other listed factors shift it right, facilitating O2 unloading to tissues.

Surfactant reduces alveolar surface tension, especially in smaller alveoli, stabilizing them and increasing overall lung compliance.

Laplace's law (P = 2T/r) shows smaller alveoli (smaller radius) would collapse more easily without surfactant to reduce surface tension.

Compliance (delta V/delta P) reflects the ease of lung expansion; low compliance means a stiffer lung requiring more pressure for the same volume change.

Restrictive disease reduces both FEV1 and FVC proportionally, so the FEV1/FVC ratio remains normal or may even increase.

Airway obstruction reduces FEV1 disproportionately more than FVC, lowering the FEV1/FVC ratio.

A normal FEV1/FVC ratio is approximately 80%, reflecting normal airway function.

The Bohr equation calculates physiological dead space from arterial and expired CO2 concentrations.

Anatomical dead space (conducting airways not participating in gas exchange) is approximately 150 mL.

Tidal volume (Vt) at rest is approximately 500 mL per breath in an average adult.

Kulchitsky cells are neuroendocrine cells that can secrete bioactive amines/peptides and are the presumed cell of origin for bronchial carcinoid tumors and small cell lung carcinoma.

Both visceral and parietal pleura are lined by a single layer of simple squamous mesothelial cells.

The olfactory epithelium is unique in containing bipolar sensory neurons whose axons form the olfactory nerve (CN I).

The vestibule is continuous with facial skin and contains vibrissae (hairs), lined by keratinized stratified squamous epithelium.

Unlike most of the respiratory tract, the vocal folds are covered by stratified squamous epithelium to withstand vibration and contact.

Smooth muscle (trachealis) bridges the open posterior ends of the tracheal cartilage rings, adjacent to the esophagus.

The thin blood-air barrier consists of the alveolar Type I cell, a fused basal lamina, and capillary endothelial cell, allowing rapid gas diffusion.

Alveolar macrophages engulf inhaled particulate matter and pathogens, and may accumulate hemosiderin in heart failure ("heart failure cells").

Clara cells secrete components of surfactant, detoxify xenobiotics via cytochrome P450 enzymes, and act as bronchiolar progenitor cells.

Tracheal rings are C-shaped hyaline cartilage, open posteriorly where the trachealis smooth muscle lies.

DPPC is the principal surface-tension-reducing phospholipid in surfactant.

Type II pneumocytes secrete surfactant and can proliferate to replace damaged Type I cells.

Type I pneumocytes are extremely thin squamous cells that cover about 95% of the alveolar surface, optimized for gas diffusion.

Terminal and respiratory bronchioles are lined by simple cuboidal epithelium, often with Clara (club) cells.

The trachea and main bronchi are lined by respiratory epithelium: pseudostratified ciliated columnar with interspersed goblet cells.

Conditions reducing thoracic space or amniotic fluid volume (e.g., oligohydramnios, diaphragmatic hernia) impair normal lung growth, causing pulmonary hypoplasia.

The septum transversum forms the central tendon, with contributions from pleuroperitoneal folds, dorsal esophageal mesentery, and body wall.

The epiglottis forms from mesenchyme of the 3rd and 4th pharyngeal arches (hypobranchial eminence).

The lung bud bifurcates into two bronchial buds, the precursors of the right and left main bronchi.

Insufficient surfactant production (common in premature infants before adequate canalicular/saccular maturity) increases alveolar surface tension, causing alveolar collapse.

The posterolateral Bochdalek defect is the most common site of congenital diaphragmatic hernia, more frequent on the left.

The 4th and 6th pharyngeal arches contribute cartilage and musculature to the larynx.

Alveoli continue to form and mature until approximately 8 years of age, allowing catch-up lung growth after preterm birth.

The canalicular stage (weeks 16-25) is when respiratory bronchioles and vascularization needed for gas exchange develop.

During the pseudoglandular stage (weeks 5-17), the lung resembles an exocrine gland as conducting airways form.

Surfactant production begins in the canalicular stage (weeks 16-25) and increases through the saccular stage.

The saccular stage (~weeks 24-38) is marked by the formation of terminal saccules and thinning of the epithelium for gas exchange.

Failure of proper tracheoesophageal septation leads to a persistent communication (fistula) between the trachea and esophagus.

The lung bud arises as an outgrowth from the ventral wall of the foregut endoderm around week 4.

The respiratory epithelium and glands arise from endoderm; surrounding connective tissue, cartilage, and muscle arise from splanchnic mesoderm.

Both lungs contain an oblique fissure separating the lower lobe from the upper (and middle, on the right) lobe.

The visceral pleura is adherent to and invests the lung surface, including within the fissures.

The aortic hiatus lies at T12, behind the diaphragm, transmitting the aorta, thoracic duct, and azygos vein.

The esophageal hiatus is at T10, transmitting the esophagus and vagal trunks.

The caval opening is at T8, transmitting the IVC and right phrenic nerve branches.

The phrenic nerve arises mainly from C4 with contributions from C3 and C5 ("C3, 4, 5 keeps the diaphragm alive").

The lung hilum, where the root structures enter/exit, lies opposite T5-T7 vertebrae.

The horizontal fissure separates the upper and middle lobes and is present only in the right lung.

The left lung typically has 8 bronchopulmonary segments due to fusion of some segments compared to the right lung.

The right lung has 10 bronchopulmonary segments (3 in upper, 2 in middle, 5 in lower lobe).

The right main bronchus is shorter, wider, and more vertical, making it the more common site for aspirated foreign bodies.

The tracheal bifurcation (carina) occurs at the level of the sternal angle, approximately T4-T5.

The internal laryngeal nerve (branch of superior laryngeal nerve) supplies sensation above the vocal folds; below is supplied by the recurrent laryngeal nerve.

Vocal folds attach anteriorly to the internal surface of the thyroid cartilage laminae and posteriorly to the arytenoid cartilages.

The cricoid is the only laryngeal cartilage that forms a complete ring, providing structural support to the airway.