RS

Question 1

Why can supplemental oxygen decrease respiratory rate in patients with COPD

Answer 1

in long-standing COPD, chronic CO₂ retention reduces sensitivity to PaCO₂. These patients rely more on hypoxemia (low PaO₂) to stimulate breathing. Supplemental oxygen raises PaO₂, reducing peripheral chemoreceptor stimulation → ↓ respiratory drive.

(healthy person depends on paco2)

Question 2

IMPORTANT What are the roles of peripheral and central chemoreceptors in respiratory regulation?

Answer 2

Peripheral chemoreceptors (carotid and aortic bodies): Respond to low PaO₂

Central chemoreceptors (medulla): Respond to high PaCO₂ via CSF pH changes ( co2 cross BBB)
Together, they send input to the medullary respiratory center to adjust breathing depth and rate

also Cerebral blood flow (CBF) remains relatively constant over a wide range of perfusion pressures (cerebrovascular autoregulation) and is mainly influenced by arterial blood gas levels, particularly changes in PaCO2. Hypercapnia triggers an increase in CBF (to aid in removal of toxins), and hypocapnia triggers a decrease in CBF.

In fact, because hypocapnia decreases CBF, mechanically ventilated patients with cerebral edema are often hyperventilated to decrease intracranial pressure and help prevent brain herniation.

Question 3

What are the types of airway mechanoreceptors and their associated functions or reflexes?

Answer 3

1-PULMONARY STRETCH RECEPTORS
Respond to lung inflation → trigger HERING–BREUER REFLEX → ↓ RESPIRATORY RATE by inhibiting inspiration

2-IRRITANT RECEPTORS
Detect irritants (e.g., smoke, dust) → COUGH, BRONCHOCONSTRICTION, ↑ MUCUS SECRETION, RAPID SHALLOW BREATHING

3-JUXTACAPILLARY (J) RECEPTORS
Activated by PULMONARY EDEMA or congestion → cause RAPID SHALLOW BREATHING and DYSPNEA

4-UPPER AIRWAY RECEPTORS
(e.g., in pharynx/larynx)
Trigger PROTECTIVE REFLEXES: COUGH, SNEEZE, APNEA, LARYNGEAL CLOSURE in response to foreign bodies or touch

Question 4

lung clears inhaled inorganic dust,

Answer 4

1-LARGE PARTICLES are trapped in MUCUS within the TRACHEA, BRONCHI, and PROXIMAL BRONCHIOLES, then cleared by CILIARY ACTION toward the PHARYNX.

2-FINE PARTICLES (<2 µm) reach the ALVEOLI, where they are PHAGOCYTOSED BY ALVEOLAR MACROPHAGES. In COAL WORKER PNEUMOCONIOSIS, these particles accumulate, leading to CHRONIC INFLAMMATION AND INTERSTITIAL FIBROSIS.

Question 5

minute ventilation (VE) and alveolar ventilation (VA)

Answer 5

VE = TV RR
VA=(TV-DEAD SPACE)RR
DEAD SPACE=TV* [PaCO2 − PeCO2]/PaCO2)
which paCO2 arterial /PeCO2 expiratory

Question 6

Cystic fibrosis

Answer 6

mutations in the CF transmembrane conductance regulator (CFTR) gene.

The CFTR protein is a transmembrane ATP-gated chloride channel

reduces chloride secretion and increases sodium absorption by the respiratory epithelia, resulting in dehydrated mucus. When saline is applied to the nasal mucosa, the increased sodium absorption in patients with CF causes a more negative nasal transepithelial potential difference, which can be used to diagnose cystic fibrosis.

IMPORTANT Patients with cystic fibrosis (CF) produce eccrine sweat with higher-than-normal concentrations of sodium and chloride. Exposure to high temperature or exercise can lead to hyponatremia and hypochloremia due to excessive sodium chloride loss through sweat; therefore, salt supplementation is recommended.

CF PFT RESULT LIKE COPD :
↑RV AND TLC
↓FEV1/FVC AND FVC

Defect:
This mutation causes impaired post-translational processing (IMPORTANT)
Misfolded CFTR protein → abnormal glycosylation (IMPORTANT) → targeted for proteasomal degradation.
Results in almost no CFTR at apical membrane of exocrine ductal epithelial cells.
Rare proteins that reach the surface have reduced channel opening.

CFTR-Modulating Drugs:

Lumacaftor → Corrector → improves protein folding & trafficking → ↑ number of CFTR proteins at membrane.

Ivacaftor → Potentiator → ↑ channel opening probability → better chloride transport.

Question 7

What are the 5 major causes of hypoxemia

Answer 7

A–a Gradient: Normal (4-15mmhg):

1-ALVEOLAR HYPOVENTILATION
Cause: ↓ Respiratory drive (e.g., CNS depression, neuromuscular disease, OBESITY)

2-LOW INSPIRED OXYGEN (FiO₂)
Cause: High altitude or suffocation

A–a Gradient: Increased:

3-VENTILATION–PERFUSION (V/Q) MISMATCH
Cause: COPD, pneumonia, PE

4-DIFFUSION IMPAIRMENT
Cause: Interstitial lung disease, pulmonary fibrosis

5-RIGHT-TO-LEFT SHUNT
Cause: Congenital heart disease, pulmonary AV malformations

Question 8

Cyanide intoxication

Answer 8

Cyanide inhibits oxidative phosphorylation by inhibiting ferric iron (Fe3+) in cytochrome c oxidase,

lowering O2 consumption in peripheral tissue.

venous O2 content rises and the arterial-venous O2 gradient falls. يعني بخلي الاوكسيجين محمل بخلايا الدم

Question 9

LUNG TRANSPLANT – COMPLICATIONS

Answer 9

✅ 1. CHRONIC REJECTION (BRONCHIOLITIS OBLITERANS)
TIMING: MONTHS TO YEARS AFTER TRANSPLANT
SYMPTOMS: PROGRESSIVE DYSPNEA, DRY COUGH
PFTs: OBSTRUCTIVE PATTERN (↓FEV1, ↓FEV1/FVC)
PATHOLOGY: LYMPHOCYTIC INFLAMMATION → GRANULATION → FIBROSIS OF SMALL AIRWAYS

⚠️ 2. ACUTE REJECTION
TIMING: WITHIN <6 MONTHS
OFTEN ASYMPTOMATIC
DETECTED ON BIOPSY
HISTOLOGY: PERIVASCULAR & INTERSTITIAL MONONUCLEAR CELL INFILTRATES

🦠 3. INFECTION
MOST COMMON CAUSE OF DEATH POST-TRANSPLANT
PATHOGENS:
CMV (MOST SERIOUS): CAUSES “OWL’S EYE” INTRANUCLEAR INCLUSIONS
BACTERIAL, FUNGAL, AND VIRAL (E.G., HSV, EBV, RSV)
PRESENTATION: FEVER, COUGH, INFILTRATES ON IMAGING

💥 4. ISCHEMIA-REPERFUSION INJURY
TIMING: WITHIN FIRST FEW DAYS POST-OP
CAUSE: SURGICAL TRAUMA + ISCHEMIA
FINDINGS: NON-CARDIOGENIC PULMONARY EDEMA, DIFFUSE ALVEOLAR DAMAGE

♻️ 5. RECURRENCE OF PRIMARY DISEASE
SOME DISEASES CAN RECUR IN THE TRANSPLANTED LUNG:
COPD
PULMONARY HYPERTENSION
SARCOIDOSIS
RARELY THE PRIMARY CAUSE OF POST-TRANSPLANT SYMPTOMS

Question 10

Histoplasma capsulatum

Answer 10

Pathogenesis:
Inhaled as mold → converts to yeast in lungs
Phagocytosed by alveolar macrophages
Survives intracellularly by inhibiting phagolysosome formation & acidification
Spreads via lymphatics and reticuloendothelial system (lungs → SPLEEN/liver)

🛡️ Immune Response:
After ~2 weeks: cell-mediated immunity forms granulomas
GRANULOMAS eventually fibrose and CALCFI

📸 Imaging Clues:
CALCIFIED LUNG, mediastinal, and splenic lesions
Often incidental findings in asymptomatic patients

👤 Common Scenario:
Healthy patient, ASYMPTOMATIC, incidental CALCIFICATION on imaging

Question 11

Surfactant & Lamellar Bodies

Answer 11

Type II pneumocytes
→ Synthesize, store, and recycle surfactant in lamellar bodies

🧪 Surfactant Composition:
Lipoprotein (mainly phospholipids like dipalmitoylphosphatidylcholine + surfactant proteins)

🛠️ Mechanism:
Stored in lamellar bodies
Released by exocytosis into alveoli
Forms tubular myelin (organized lattice)
Spreads into a film at the air-liquid interface
Reduces alveolar surface tension → prevents collapse
Recycled via endocytosis for reuse

Surfactant is a lipoproteinaceous material that appears pink with periodic acid–Schiff staining

⚠️ Clinical Relevance:
Low lamellar body count = Surfactant deficiency
→ Seen in premature infants
→ Leads to Neonatal Respiratory Distress Syndrome (NRDS)
↑ Surface tension → alveolar collapse (atelectasis)
Rapid-onset respiratory failure after birth

Question 12

Chronic Bronchitis & the Reid Index

Answer 12

🧪 Pathology:
Increased mucus production
Bronchial wall thickening due to submucosal gland hyperplasia

📏 Reid Index:
Definition:
Ratio = (Thickness of submucosal glands) / (Thickness from epithelium to cartilage)
Normal: ≤ 0.4
↑ Reid index: Indicates SEVIRITY& chronicity of chronic bronchitis

Question 13

Types of Pneumonia (Morphologic Patterns)

Answer 13

1)Lobar
Entire lobe uniformly involved
Alveolar exudate; stages as above
Streptococcus pneumoniae

2)Bronchopneumonia
Patchy, multilobar
Infection starts in bronchioles, spreads to alveoli Staph aureus, Klebsiella, H. influenzae

3)Interstitial (Atypical)
Diffuse, in interstitium
Minimal alveolar exudate; perivascular/interstitial inflammation
Mycoplasma, Chlamydia, viruses

Question 14

Lobar Pneumonia STAGES

Answer 14

1)Congestion
Day 0–2
↑ Capillary permeability → alveolar fluid + RBCs + neutrophils
Heavy, red, boggy lobe

2)Red hepatization
Day 2–4
Fibrin + neutrophils + RBCs form solid exudate Firm, red, liver-like

3)Gray hepatization
Day 4–7
RBCs disintegrate, ↑ macrophages
Gray, dry, firm

4)Resolution
>7 days
Macrophages remove debris; tissue returns to normal
Restored architecture (~3 weeks)

Question 15

V/Q Ratio

Answer 15

Highest at apex =3

Lowest at base =0.6

Ventilation: Gravity stretches lungs downward → more air goes to base. (SLINKY EFFECT)

Perfusion: Gravity increases hydrostatic pressure → more blood flows to base

IMPORTANT :Density Effect: Blood is denser than air → perfusion gradient (apex → base) is steeper than ventilation يعني الدم اثقل لتحت

Question 16

V/Q in exercise

Answer 16

20V/8Q
so ventilation increased more

VE (minute ventilation) INCREASES

mixed Venous O2 content DECRESES (muscles extract more oxygen from the blood)

Question 17

AIRWAY RESISTANT

Answer 17

UPPER>LOWER

Medium-sized bronchi (highest resistance)
🔸 Due to turbulence and fewer parallel pathways.

Segmental bronchi

TRACHEA

Smaller bronchioles

Terminal bronchioles
🔸 Low individual resistance but very high number → low total resistance.

Respiratory bronchioles & alveolar ducts (lowest resistance)
🔸 Vast cross-sectional area allows smooth airflow.

Question 18

Radial traction

Answer 18

Radial traction refers to the outward pulling force exerted by elastic recoil of surrounding lung tissue on the airways.

INCREASES with lung expansion → more traction = wider airways = less resistance. AND IN RESTRICTIVE DISEASES

LOST(DECREASES) in OBSTRUCTIVE diseases like emphysema → ↓ elastic recoil → ↓ radial traction → airway collapse, especially during expiration.
(supernormal expiratory flow rates)

Question 19

Kaposi Sarcoma (KS)

Answer 19

Caused by Human Herpesvirus 8 (HHV-8)
Common in immunosuppressed (esp. HIV/AIDS patients)

Clinical Features:
Skin lesions: Purple papules/plaques, often on lower extremities
Visceral involvement:
GI tract: Abdominal pain
Pulmonary system: Cough, hemoptysis, dyspnea, pleural effusion
Airway lesions: May cause obstruction (ENDOBRONCHIAL )

Diagnosis:
Biopsy:
Spindle-shaped endothelial cells
Slit-like vascular spaces
Extravasated RBCs, inflammatory cells

Chest imaging: Reticular opacities or nodular densities

Bronchoscopy: Cherry-red or violaceous macules/papules in bronchi

Question 20

Pulmonary Infections in Immunocompromised Patients

Answer 20

1. Cytomegalovirus (CMV):

Organism: DNA virus (Herpesviridae)
Symptoms: Cough, dyspnea, fever

Histology:
Cytopathic effect:

Cell enlargement (cytomegaly)
Intranuclear & intracytoplasmic inclusions (“owl’s eye” nuclei)

2. Pneumocystis jirovecii:
   Organism: Fungus (not a protozoa)
   Symptoms: Cough, dyspnea, fatigue

Histology:

Interalveolar foamy exudate
Cup- or crescent-shaped organisms
Stains: Silver stain

Question 21

Common triggers of asthma

Answer 21

1) Inhaled allergens
Animal dander
Dust mites & cockroaches
Pollens & molds

2) Respiratory irritants
Cigarette smoke & air pollutants
Perfumes

3) Medications
Aspirin/NSAIDs
Nonselective ꞵ blockers

4) Other
Upper respiratory tract infection
Exercise & cold, dry air
Gastroesophageal reflux disease

Question 22

GI AND RS = CF

Answer 22

MECONIUM ILEUS is a distal small bowel obstruction due to abnormally dehydrated meconium in a patient with CYSTIC FIBROSIS (CF). Persistent, treatment-resistant infectious PNEUMONIAS , bronchiectasis, and cor pulmonale account for most deaths due to CF.

CF → fat-soluble vitamin loss → avitaminosis A → squamous metaplasia of mucosal surfaces

NORMALLY Vitamin A Role:
Maintains mucus-secreting columnar epithelium in:
Conjunctiva, respiratory tract, urinary tract, pancreatic ducts

Question 23

Asbestos Exposure AND CANCER

Answer 23

Asbestosis (interstitial fibrosis)

Pleural plaques (benign)

Malignancies:
✅ Bronchogenic carcinoma – Most common
✅ Mesothelioma – Most specific

Question 24

Systemic Sclerosis (Scleroderma)

Answer 24

1)Limited Cutaneous (CREST):
Calcinosis cutis
Raynaud phenomenon
Esophageal dysmotility
Sclerodactyly
Telangiectasia

2)Diffuse Cutaneous:
More widespread skin involvement
Associated with Interstitial Lung Disease (ILD) ✅

IMPORTANT Pulmonary Complications:
Limited Cutaneous: 🫀 Pulmonary Arterial Hypertension (PAH)
Leading cause of death in systemic sclerosis
Vascular remodeling → onion-skin concentric thickening
⬆ Afterload → Right heart failure

Diffuse Cutaneous: 🫁 Interstitial Lung Disease (ILD)

Question 25

Elastase

Answer 25

Elastase Types & Sources: 1)Neutrophil Elastase Stored in azurophilic granules Inhibited by: 🧬 α1-antitrypsin (serum) 2)Macrophage Elastase Stored in lysosomes Inhibited by: 🧬 Tissue inhibitors of metalloproteinases (TIMPs) Pathogenesis of Emphysema: Excess elastase activity → alveolar wall destruction 🏥 Clinical Forms: Panacinar emphysema: Associated with α1-antitrypsin deficiency Centriacinar emphysema: Associated with smoking-induced neutrophilic infiltration

Question 26

Lung Abscess -IMPORTANT

Answer 26

Lung Abscess – Main Causes: ASPIRATION (most common) Necrotizing bacterial pneumonia (e.g., Staph aureus, Klebsiella) Septic emboli (ENDOCARDITIS IV USERS) Bronchial obstruction (e.g., tumor) Immunocompromised infections (e.g., Nocardia, fungi) 🔍 Most Common Cause: IMPORTANT Aspiration of ANAEROBIC oral bacteria: Peptostreptococcus Prevotella Bacteroides Fusobacterium ⚠️ Risk Factors (⬆ Aspiration): Alcoholism Drug abuse Seizure disorders Previous stroke Dementia Symptoms (Often Indolent): Fever Night sweats Weight loss **Cough with FOUL SMELLING SPUTUM Pneumonia VS Pneumonitis Pathophysiology Pneumonia Lung parenchyma infection Aspiration of upper airway or stomach microbes (anaerobes) Pneumonitis Lung parenchyma inflammation Aspiration of gastric acid with direct tissue injury Clinical features Pneumonia Present days after aspiration event Fever, cough, ↑ sputum CXR infiltrate in dependent lung segment (classically RLL) Can progress to abscess Pneumonitis Present hours after aspiration event Range from no symptoms to nonproductive cough, ↓ O2, respiratory distress CXR infiltrates (one or both lower lobes) resolve without antibiotics Management Pneumonia Antibiotics: clindamycin or beta-lactam & beta-lactamase inhibitor Pneumonitis Supportive (no antibiotics) Abscess formation is largely driven by NEUTROPHILS recruitment and activation leading to the release of cytotoxic granules (lysosomes) that kill bacteria but also cause liquefying necrosis of surrounding tissue.

Question 27

Septic Pulmonary Emboli

Answer 27

Common Cause: Tricuspid valve endocarditis (especially in IV DRUG USERS) Most common pathogen: Staphylococcus aureus ⚠️ Pathophysiology: Vegetation fragments embolize → lodge in pulmonary arterial tree Result in septic pulmonary infarcts WEDGE SHAPED HEMORRHAGIC infarcts seen in lung periphery 🔬 Why Hemorrhagic? Dual blood supply: Pulmonary + bronchial arteries Low lung tissue density → allows blood to seep in Infarcts = hemorrhagic (RED), not pale VS PE THE DIFFERANCE IS IN RISK FACTORS

Question 28

Obstructive Atelectasis

Answer 28

Clinical Presentation: Decreased breath sounds on affected side Hemithorax opacification on CXR Tracheal deviation TOWARD the opacified side ✅ 🧫 Common Causes: 1)Mucus plugging Seen in COPD, bronchiectasis, post-op states 2)Central lung cancer (e.g., squamous cell carcinoma) OBSTRUCTS right mainstem bronchus

Question 29

Bronchopulmonary Dysplasia (BPD)

Answer 29

Seen in premature infants Due to arrest in lung development during the saccular stage (normally: 26–36 weeks gestation) 🧫 Pathophysiology: 1)Impaired alveolarization 🫁 Fewer, dilated alveoli ↓ Septation 2)Abnormal vasculogenesis 🩸 Dysmorphic alveolar capillaries

Question 30

Pulmonary Hamartoma

Answer 30

Often discovered INCIDENTALLY on imaging Most common BENIGN pulmonary tumor MIDDLE-AGED adults, Usually ASYMPTOMATIC 📸 Imaging Features (Chest X-ray/CT): SOLITARY, well-circumscribed "COIN LESION" <3 CM in size Classic "POPCORN" pattern of CALCIFICATION Typically PERIPHERAL, SLOW-GROWING IMPORTANT 🔬 Histology: Nodules of MATURE CONNECTIVE TISSUE: CARTILAGE, FAT, fibrous tissue Clefts lined by ENTRAPPED RESPIRATORY EPITHELIUM

Question 30

lobar consolidation with V/Q

Answer 30

The normal response to local alveolar hypoxia is hypoxic pulmonary vasoconstriction (HPVC). Pulmonary arterioles detect hypoxia, vasoconstricting in response. This limits blood flow to the hypoxic nonventilated alveoli, redirecting it toward better-ventilated ones. Therefore, HPVC mitigates V/Q mismatch, optimizing oxygenation. However, HPVC is impaired by inflammatory states such as acute pneumonia or sepsis. Proinflammatory cytokines cause regional vasodilation, resulting in hyperemia (↑ perfusion) to affected lung areas, further lowering the V/Q ratio and worsening the hypoxemia. Once treatment is initiated (eg, antibiotic therapy), vasoactive inflammatory mediators are downregulated over the ensuing hours to days, and HPVC is restored. This occurs prior to resorption of alveolar debris and fibrinous edema, a slower process carried out by alveolar macrophages. Therefore, oxygenation typically improves days to weeks before resolution of the pneumonic infiltrates (eg, clear x-ray), which is consistent with this patient's improved oxygenation despite unchanged crackles and egophony

Question 31

Radiation-Induced Lung Injury

Answer 31

Occurs after thoracic irradiation (e.g., for breast, lung, or lymphoma treatment) Involves injury to pneumocytes and vascular endothelial cells 🧬 Pathophysiology: Damage triggers inflammatory cytokines: IL-1, TNF-α, TGF-β Leads to: ARDS تقريبا Acute phase: Exudative alveolitis, hyaline membrane formation Chronic phase: Progressive fibrosis

Question 32

Prone Positioning

Answer 32

Used in severe Acute Respiratory Distress Syndrome (ARDS) Goal: Improve arterial oxygenation 🧬 Mechanism of Action: Reduces posterior alveolar atelectasis IMPROVES V/Q MISMATCHING Decreases intrapulmonary shunting ⚠️ Supine Position (Face-Up) Issues: Heart and anterior lung compress posterior lung Abdominal mass pushes diaphragm upward (cranially) Leads to posterior lung collapse (atelectasis) Anterior alveoli may become hyperinflated → ↑ barotrauma risk

Question 33

Asthma

Answer 33

Classic sputum findings: Eosinophils Charcot-Leyden crystals (formed from eosinophil membrane proteins) Immunologic mechanism: IL-5 secreted by TH2-type CD4+ T cells recruits and activates eosinophils. Type I hypersensitivity reactions are an allergic response triggered by the binding of previously recognized antigen to IgE antibodies on mast cells. In the early phase of the response, HISTAMINE, already stored in preformed granules in mast cells, is the first chemical mediator released. Once released, histamine stimulates smooth muscle contraction (bronchoconstriction), increases vascular permeability (edema), and increases mucus secretion. Major basic protein is released from eosinophils in the late stage of a type I hypersensitivity reaction and causes localized tissue damage.

Question 34

myasthenic crisis and respiratory failure

Answer 34

Myasthenic crisis: Life-threatening exacerbation of myasthenia gravis causing respiratory muscle weakness and global hypoventilation. Key findings: Respiratory failure: Low pH, high CO₂, low O₂ Symptoms: Ptosis, bulbar weakness (e.g., dysphonia), low FVC Pathophysiology: Autoantibodies against postsynaptic nicotinic ACh receptors ↓ Receptor density → ↓ response to ACh despite normal release Muscle fatigue with use due to ACh depletion Triggers: Illness, infection, AChE inhibitor withdrawal Treatment: Acetylcholinesterase inhibitors (e.g., pyridostigmine) + supportive care

Question 35

green color of sputum in community-acquired pneumonia (CAP) AND OTHER COLORS

Answer 35

Green sputum color is due to MYELOPEROXIDASE , a blue-green heme enzyme in neutrophils that forms hypochlorous acid during the respiratory burst. Most common CAP cause: Streptococcus pneumoniae Other sputum colors: Currant jelly (Klebsiella): RBC/hemoglobin leakage from necrosis Rusty (Pneumococcus): RBC extravasation Blue-green (Pseudomonas): Pyocyanin pigment (rare in healthy adults)

Question 36

epiglottitis

Answer 36

Cause: Most commonly Haemophilus influenzae type b Presentation: High fever, toxic appearance Respiratory distress with tripod positioning Inspiratory stridor due to supraglottic (laryngeal) obstruction Pathophysiology: Inspiration → ↑ airflow speed → ↓ intraluminal pressure → airway collapses further → turbulent flow → stridor Tripod position improves airflow by pulling the tongue forward

Question 37

LUNG SOUND

Answer 37

Breath Sound Differentiation: 1)Inspiratory stridor: Obstruction at/above larynx (e.g., epiglottitis, laryngomalacia) Heard during inspiration due to airway collapse from negative pressure 2) Expiratory stridor: Obstruction in intrathoracic trachea (e.g., tracheomalacia) Worsens with expiration due to positive intrathoracic pressure 3) Wheezing: High-pitched sound from small airway narrowing (e.g., asthma) Heard mainly during expiration 4) Rhonchi: Low-pitched, rattling sounds from bronchi filled with secretions Heard on both inspiration and expiration

Question 38

Abnormal oxygen metabolism in sepsis

Answer 38

1)↓ Global O2 delivery Hypovolemia: ↓ ECBV (capillary leak) Hypoxemia: ↓ PaO2 (ARDS) 2) ↓ Microcirculatory O2 extraction Vasodilation: rapid shunting of blood through organs Edema: ↓ O2 diffusion (↑ interstitial distance) Microthrombosis: capillary obstruction 3)↓ Mitochondrial O2 use ROS ⇄ mitochondrial damage & ↓ ETC function Result: ↓ oxidative phosphorylation & ↓ ATP production

Question 39

equilibrium at functional residual capacity (FRC) and pneumothorax

Answer 39

At FRC: Lung: Inward collapsing force Chest wall: Outward expanding force These opposing forces balance → negative intrapleural pressure Keeps lungs expanded and chest wall contained → defines FRC Loss of negative pressure (e.g., pneumothorax): Lung collapses → ↓ lung volume Chest wall expands → ENLARGED HEMITHORAX Net effect: ↓ FRC (due to lung collapse reducing air volume at rest) Inspiratory compliance ↓ due to loss of lung expansion ability

Question 40

ARDS and PEEP

Answer 40

ARDS Pathophysiology: Inflammatory lung injury → alveolar-capillary leakage Leads to pulmonary edema, alveolar collapse, and ↓ ventilation Causes intrapulmonary shunting (perfusion without ventilation) ↓ Functional Residual Capacity (FRC) PEEP (Positive End-Expiratory Pressure): Applied during mechanical ventilation Prevents alveolar collapse during expiration Reopens collapsed alveoli → ↓ intrapulmonary shunting Increases FRC toward normal → Improves oxygenation Enhances lung compliance Reduces work of breathing

Question 41

pulmonary arterial hypertension (PAH)

Answer 41

Hereditary PAH (2-hit model): 1)BMPR2 gene mutation → predisposes to endothelial injury & smooth muscle proliferation 2)Environmental trigger (e.g., infection, drugs) → initiates disease → Leads to vascular remodeling → ↑ pulmonary vascular resistance → progressive PAH IMPORTANT General Pathophysiology: Endothelial dysfunction → ↑ Vasoconstrictors (endothelin, thromboxane A₂) ↓ Vasodilators (nitric oxide, prostacyclin) → Vasoconstriction + smooth muscle proliferation → intimal thickening → ↑ pulmonary artery pressure → eventual right-sided heart failure Treatment (targets mediator imbalance): Endothelin receptor antagonists (e.g., bosentan) Prostacyclin analogs (e.g., epoprostenol) PDE-5 inhibitors (e.g., sildenafil) Goal: ↓ vasoconstriction, ↑ vasodilation, inhibit vascular remodeling

Question 42

functions and components of eosinophils

Answer 42

Morphology: Bilobed nucleus Cytoplasm filled with eosinophilic granules Functions: Defense against parasitic infections Involved in allergic reactions (e.g., asthma, eosinophilic esophagitis) Granule content: Major basic protein (MBP) Potent antihelminthic toxin Damages epithelial and endothelial cells Key contributor to chronic lung damage in asthma through tissue toxicity and inflammation

Question 43

radon and lung cancer

Answer 43

Radon (²²²Rn): Colorless, odorless, radioactive gas from uranium decay in soil/rock Enters homes via cracks or contaminated groundwater Accumulates in basements and lower levels Carcinogenic mechanism: Emits alpha particles (potent DNA-damaging ionizing radiation) #2 cause of lung cancer in the US #1 environmental risk for nonsmokers

Question 44

Hepatic hydrothorax:

Answer 44

Hepatic hydrothorax: Right-sided transudative pleural effusion in a patient with cirrhosis and ascites Pathophysiology: Ascitic fluid moves into the pleural space through small diaphragmatic fenestrations Most commonly affects the right hemithorax Driven by: ↑ Hydrostatic pressure from portal hypertension ↓ Oncotic pressure from hypoalbuminemia Pleural fluid type:Transudative

Question 45

How does smoking affect lung function over time, and what happens to lung decline after smoking cessation

Answer 45

Normal aging: Lung function (FEV₁) peaks ~age 30 Declines slowly (~25 mL/year) thereafter In smokers: Lung function declines 3× faster due to: Airway inflammation → chronic bronchitis → ↑ airway resistance Alveolar destruction → emphysema → ↓ elastic recoil Result: Expiratory flow limitation and accelerated FEV₁ decline After smoking cessation: No lung function is regained But the rate of FEV₁ decline slows to that of nonsmokers Represents a change in slope, not a reversal

Question 46

Pleuritic Chest Pain

Answer 46

Sharp, localized, worse with inspiration, cough, or movement Caused by parietal pleura irritation (visceral pleura = no pain fibers) Parietal Pleura & Innervation: Costal pleura – thoracic wall → intercostal nerves → pain felt locally Mediastinal pleura – phrenic nerve (C3–C5) → referred pain to neck/shoulder Diaphragmatic pleura –IMPORTANT Central part → phrenic nerve (C3–C5) → neck/shoulder Peripheral part → intercostal nerves → local pain Cervical pleura – extends into neck Referred Pain Rule: Phrenic nerve (C3–C5) → neck & shoulder Intercostal nerves → pain near chest wall

Question 47

aspiration pneumonia MAYPE REPEATED

Answer 47

Due to gravity, aspiration pneumonia typically develops in the most dependent portions of the lung. Patients who aspirate while lying supine typically have involvement of the posterior segments of the upper lobes and the superior segments of the lower lobes. The right lung is more prone to aspiration than the left lung as the right main bronchus has a larger diameter, is shorter, and is more vertically oriented than the left main bronchus (mnemonic: "Inhale a bite, goes down the right").

Question 48

ANATOMY -HISTO

Answer 48

Bronchi have a ciliated pseudostratified columnar epithelium with mucin-secreting goblet cells and submucosal mucoserous glands. The airway epithelium gradually changes to ciliated simple cuboidal by the level of the terminal bronchioles. Bronchioles lack glands and cartilage, and the number of goblet cells decreases distally, ending before the terminal bronchioles. Ciliated epithelium persists up to the respiratory bronchioles.

Question 49

Chest Tube Insertion

Answer 49

Chest Tube Insertion Site: 4th or 5th intercostal space Anterior or midaxillary line Safe triangle: avoids diaphragm, major vessels, abdominal organs Structures Traversed: Skin Subcutaneous fat Serratus anterior muscle IMPORTANT Intercostal muscles (external → internal → innermost) Parietal pleura → enters pleural cavity Serratus Anterior Muscle: Origin: Lateral surfaces of 1st–8th ribs Insertion: Medial border of scapula (entire length)

Question 50

Sarcoidosis – Immunopathogenesis

Answer 50

Cause: Dysregulated cell-mediated immunity to unknown antigen → noncaseating granulomas Key Cytokine Pathway: APCs release IL-12 → CD4⁺ T cells → Th1 differentiation Th1 cells release: IL-2 → autocrine proliferation of Th1, further recruitment IFN-γ → activates macrophages → granuloma formation Activated macrophages & T cells → TNF-α → leukocyte recruitment & granuloma maintenance Result:

Question 51

Elastin

Answer 51

Made as tropoelastin (≈700 mostly nonpolar (IMPORTANT) AAs: glycine, alanine, valine) Contains proline & lysine (few hydroxylated vs collagen) Secreted → binds fibrillin microfibrils (scaffold) Lysyl oxidase (Cu²⁺-dependent) → oxidatively deaminates lysine → desmosine cross-links (IMPORTANT) Cross-links + hydrophobic AAs → elastic recoil

Question 52

Haldane AND Bohr EFFECT

Answer 52

The binding of O2 to hemoglobin increases the affinity for binding of subsequent O2 molecules (cooperative binding). In the lungs, the binding of O2 to hemoglobin drives the release of H+ and CO2 from hemoglobin (Haldane effect). In the peripheral tissues, high concentrations of CO2 and H+ facilitate O2 unloading from hemoglobin (Bohr effect).

Question 53

Mycobacterium tuberculosis

Answer 53

Initial Phase: Unchecked replication inside alveolar macrophages Virulence factors (eg, cord factor) prevent phagolysosome destruction Immune Activation: Infected macrophages MCH1→ IL-12 → naïve CD4⁺ → Th1 differentiation Th1 cells migrate to infection → secrete IFN-γ → macrophage activation Macrophages: Improved intracellular killing Release TNF-α → recruit more macrophages Granuloma Formation: Activated macrophages → epithelioid cells & Langhans giant cells Surround residual bacteria → caseating granuloma (acidic, hypoxic core)

Question 54

Granuloma Formation in Sarcoidosis MCH1

Answer 54

antigen-presenting cells (APCs) (eg, alveolar macrophages, dendritic cells). Cytokine cascade: APCs (MCH1) release IL-12 → drives naïve CD4+ T cells → Th1 cells. Th1 cells release IL-2 → promotes more Th1 proliferation & recruitment. Th1 cells release IFN-γ → activates macrophages to a more bactericidal, inflammatory state. Macrophages release TNF-α → recruits additional immune cells, helps maintain granulomas.

Question 55

Selective IgA deficiency

Answer 55

Clinical features Usually asymptomatic Recurrent sinopulmonary, gastrointestinal infections (IMPORTANT) Autoimmune disease Anaphylaxis during transfusions Diagnosis Low or absent serum IgA levels Normal IgG & IgM levels

Question 56

Hypersensitivity reactions

Answer 56

Type I – Immediate Humoral: IgE Cellular: Basophils, Mast cells Mechanism: Antigen cross-links IgE on mast cells → histamine & other mediators released within minutes. Examples: Anaphylaxis, Allergic rhinitis, Asthma. Type II – Cytotoxic Humoral: IgG & IgM autoantibodies, Complement activation Cellular: NK cells, Eosinophils, Neutrophils, Macrophages Mechanism: Antibodies bind antigens on cell surface → cell destruction via complement or ADCC. Examples: Autoimmune hemolytic anemia, Goodpasture syndrome, Myasthenia gravis. Type III – Immune Complex Humoral: Antigen–antibody complexes, Complement activation Cellular: Neutrophils Mechanism: Immune complexes deposit in tissues → complement activation → inflammation & tissue damage. Examples: Serum sickness, Poststreptococcal glomerulonephritis, Lupus nephritis. Type IV – Delayed Humoral: None Cellular: T cells (CD4+ Th1 & CD8+), Macrophages Mechanism: Antigen-presenting cells activate T cells → cytokine release → macrophage activation & tissue damage (onset in 48–72 hrs). Examples: Contact dermatitis, Tuberculin skin test, Chronic transplant rejection.

Question 57

ASTHMA

Answer 57

Proposed mechanism: Excess Th2 activity vs Th1 → skewed immune response. Leads to: ↑ IgE production ↑ Type I hypersensitivity tendency Chronic eosinophilic bronchitis Sensitization Phase (Initial exposure): Inhaled antigen → activates Th2 cells. IL-4: Stimulates B-cells IL-13 Repeat Exposure Phase: Allergen cross-links IgE on mast cells → mast cell degranulation. Release of inflammatory mediators: Histamine Leukotrienes Eosinophil activation → release of major basic protein and other cytotoxins