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Each lung is a conical, spongy, elastic organ situated in its own pleural cavity.
The right lung is larger, shorter, and wider than the left because of the liver below and has three lobes (upper, middle, lower).
The left lung is smaller and narrower due to the presence of the heart, has two lobes (upper and lower), and a cardiac notch with a lingula.
Apex of lung: projects into the root of the neck, about 2.5 cm above the medial 1/3 of the clavicle.
Base of lung: rests on the diaphragm.
Costal surface: convex, related to ribs and intercostal muscles.
Medial surface: concave, related to mediastinum, heart, and great vessels.
Borders of lung:
Anterior border: thin and sharp; left lung has the cardiac notch here.
Posterior border: thick and rounded, corresponding to vertebral column.
Inferior border: separates the base from the costal and medial surfaces.
Right lung lobes:
Superior lobe — above horizontal fissure.
Middle lobe — between horizontal and oblique fissures.
Inferior lobe — below oblique fissure.
Left lung lobes:
Superior lobe — includes the lingula.
Inferior lobe — below oblique fissure.
Fissures of lungs:
Right lung: oblique and horizontal.
Left lung: only oblique fissure.
Cardiac notch: indentation on the anterior border of the left lung below the 4th costal cartilage.
Lingula: tongue-like projection of the upper lobe of left lung, homologous to the middle lobe of the right lung.
Root of lung contains:
1 bronchus (right has 2 — eparterial and hyparterial).
1 pulmonary artery.
2 pulmonary veins.
Bronchial vessels, lymph nodes, and nerves.
Arrangement (Right Lung): Bronchus – Artery – Bronchus – Veins (B-A-B-V).
Arrangement (Left Lung): Artery – Bronchus – Veins (A-B-V).
Bronchial tree hierarchy:
Trachea → Principal bronchus → Lobar bronchus → Segmental bronchus → Terminal bronchiole → Respiratory bronchiole → Alveolar duct → Alveolus.
Each lung has 10 bronchopulmonary segments, each aerated by an individual segmental bronchus and supplied by a segmental artery.
These segments are functionally and surgically independent.
Histology:
Bronchi: pseudostratified ciliated columnar epithelium with cartilage and glands.
Bronchioles: simple columnar to cuboidal, no cartilage or glands.
Alveoli: lined by Type I and Type II pneumocytes.
Type II cells secrete surfactant, which reduces surface tension and prevents alveolar collapse.
Developmental origin:
Endoderm: epithelium of airways and alveoli.
Splanchnic mesoderm: cartilage, muscle, and connective tissue.
Development begins in week 3 as respiratory diverticulum from foregut.
Molecular control:
TBX4 → induces lung bud formation.
FGF10 → promotes bud outgrowth.
SHH (Sonic Hedgehog) → controls branching and patterning.
Stages of lung development:
Pseudoglandular (5–17 weeks): formation of bronchioles.
Canalicular (16–25 weeks): vascularization begins.
Terminal sac (24 weeks–birth): alveoli begin forming.
Alveolar (birth–8 years): maturation of alveoli.
Clinical correlations:
Aspiration → more common in right bronchus.
Carina → sensitive ridge triggering cough reflex.
Bronchiectasis → dilation of bronchi due to infection.
Bronchogenic carcinoma → arises from bronchial epithelium.
Pulmonary embolism → blockage of pulmonary artery by a clot.
Tuberculosis → commonly affects lung apices.
Neonatal respiratory distress → due to surfactant deficiency.
Lymph drainage:
Superficial plexus: under pleura → bronchopulmonary (hilar) nodes.
Deep plexus: along bronchi → pulmonary → tracheobronchial → paratracheal nodes.
Final drainage → thoracic duct (left) or right lymphatic duct.
Nerve supply:
Parasympathetic (vagus): bronchoconstriction, vasodilation, secretion.
Sympathetic (T1–T5): bronchodilation, vasoconstriction, reduced secretion.
Blood supply:
Pulmonary arteries → deoxygenated blood to lungs.
Pulmonary veins → oxygenated blood to left atrium.
Bronchial arteries → nutrient supply to bronchial tree.
Radiological importance:
Horizontal fissure visible in PA chest X-ray at 4th costal cartilage.
Oblique fissure seen in lateral view, running from T4 to 6th costal cartilage.
Knowledge of segmental anatomy aids in interpreting collapse, consolidation, and effusion.
Case:
A child accidentally inhales a peanut while playing. The child begins to cough and shows signs of respiratory distress.
Anatomical Basis:
The right principal bronchus is shorter, wider, and more vertical, so inhaled foreign bodies commonly enter it.
Within the right lung, they most often lodge in the posterior basal segment of the lower lobe.
May lead to obstructive pneumonia or segmental collapse (atelectasis).
Case:
A patient presents with chronic productive cough, foul sputum, and recurrent chest infections.
Anatomical Basis:
Permanent dilation of bronchi due to destruction of their muscular and elastic tissue following infection or obstruction.
Commonly affects lower lobes (especially the posterior basal segments).
Segmental drainage and postural physiotherapy help prevent recurrence.
Case:
A postoperative patient develops sudden breathlessness and absent breath sounds on one side.
Anatomical Basis:
Blockage of a bronchus (by mucus, tumor, or foreign body) prevents air entry to alveoli, leading to alveolar collapse.
The mediastinum shifts toward the collapsed lung, and affected area appears opaque on X-ray.
Case:
A tall, thin young man suddenly develops chest pain and difficulty breathing.
Anatomical Basis:
Rupture of subpleural blebs or trauma allows air to enter the pleural cavity, collapsing the lung.
Tension pneumothorax occurs when air enters but cannot escape, pushing the mediastinum to the opposite side.
Requires emergency needle decompression.
Case:
A chronic smoker develops persistent cough, hemoptysis, and weight loss.
Anatomical Basis:
Cancer arises from bronchial epithelium, commonly near the hilum of the lung.
Metastasis occurs via lymph nodes (bronchopulmonary → tracheobronchial → paratracheal) and blood (to brain, bone, liver).
May compress recurrent laryngeal nerve, causing hoarseness of voice.
Case:
Bronchoscopy in a patient with lung cancer reveals a widened carina.
Anatomical Basis:
The carina (ridge at the tracheal bifurcation) is displaced or widened due to enlarged subcarinal lymph nodes in bronchogenic carcinoma.
Carina is highly sensitive; irritation produces a cough reflex via vagus nerve.
Case:
A bedridden patient suddenly develops dyspnea, chest pain, and cyanosis.
Anatomical Basis:
Thrombus from deep leg veins may travel through the inferior vena cava and right heart to block a pulmonary artery.
Leads to pulmonary infarction and sudden circulatory collapse.
Common site: lower lobar arteries.
Case:
A patient with aspiration pneumonia develops fever, cough, and expectoration of foul-smelling sputum.
Anatomical Basis:
Suppurative necrosis of lung tissue due to infection.
Common in posterior segment of upper lobe or superior segment of lower lobe (dependent areas in supine position).
Requires antibiotics and postural drainage.
Case:
A young adult presents with chronic cough, low-grade fever, and apical opacity on chest X-ray.
Anatomical Basis:
Primary focus (Ghon focus) usually develops in the upper part of the lower lobe or lower part of the upper lobe, often near the apex due to high oxygen tension.
May progress to fibrosis and cavitation.
Spread via lymphatics and bloodstream leads to miliary TB.
Case:
A worker exposed to silica dust develops progressive breathlessness and restrictive lung changes.
Anatomical Basis:
Fibrotic thickening of lung tissue leads to reduced compliance and gas exchange.
Common in silicosis, asbestosis, and coal worker’s pneumoconiosis.
Affects upper lobes in silicosis, lower lobes in asbestosis.
Case:
A patient with pneumonia develops dullness on percussion and reduced breath sounds at lung base.
Anatomical Basis:
Inflammation of the pleura leads to fluid accumulation in the costodiaphragmatic recess, compressing lung tissue.
Fluid is drained by thoracocentesis.
Case:
A long-term smoker presents with breathlessness, barrel-shaped chest, and decreased breath sounds.
Anatomical Basis:
Destruction of alveolar walls and loss of elastic tissue cause air trapping and overdistension of alveoli.
Results in poor gas exchange and chronic obstructive pulmonary disease (COPD).
Case:
A premature newborn shows labored breathing and cyanosis soon after birth.
Anatomical Basis:
Type II pneumocytes fail to produce enough surfactant, causing alveolar collapse.
Histology shows hyaline membranes lining alveoli.
Treatment involves surfactant therapy and assisted ventilation.
Case:
A patient with localized bronchiectasis undergoes removal of one bronchopulmonary segment.
Anatomical Basis:
Each bronchopulmonary segment is an independent unit with its own segmental bronchus and artery, separated by connective tissue septa.
Allows segmental resection without affecting other segments.
Case:
An X-ray shows an extra fissure in the right upper lobe, mistaken for pathology.
Anatomical Basis:
Caused by aberrant course of the azygos vein, which arches over the lung apex and forms an accessory fissure enclosing a small azygos lobe.
Clinically insignificant but important radiologically.
Case:
A patient with left lung carcinoma develops an enlarged left supraclavicular lymph node.
Anatomical Basis:
Metastatic spread from bronchogenic carcinoma via thoracic duct to the left supraclavicular node, known as Virchow’s node.
Sign of advanced malignancy.
Case:
A patient with deep vein thrombosis develops sudden pleuritic chest pain and hemoptysis.
Anatomical Basis:
Embolic occlusion of a branch of pulmonary artery causes wedge-shaped infarct, often in the lower lobes.
The apex of the infarct points toward the hilum, and the base toward the pleura.
Case:
A patient with fever and cough shows segmental opacity on X-ray.
Anatomical Basis:
Infection localized to one bronchopulmonary segment, often following obstruction or poor drainage.
Segmental structure helps in identifying and targeting the lesion.
Case:
A physiotherapist positions a patient with head-down tilt to drain secretions from the lower lobes.
Anatomical Basis:
Knowledge of segmental bronchial orientation helps in using gravity to assist mucus clearance — vital in bronchiectasis and cystic fibrosis.
Case:
A patient with left apical tumor complains of shoulder and inner arm pain.
Anatomical Basis:
Pancoast tumor at lung apex invades brachial plexus (T1) and sympathetic chain, producing shoulder pain and Horner’s syndrome (ptosis, miosis, anhidrosis).
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