Anatomy of the Lungs and Heart Quiz

Lung Fissures and Heart Position

• Oblique Fissure: A line drawn obliquely downward and outward from 1 inch (2.5 cm) lateral to the 5th thoracic vertebra to the 6th costal cartilage, approximately 1.5 inches (4 cm) from the midline. This line roughly corresponds to the medial border of the abducted scapula.
• Transverse Fissure (right lung): A horizontal line along the 4th costal cartilage, intersecting the oblique fissure where it crosses the 5th rib. This line separates the middle and upper lobes of the right lung.
• Heart Outline: Represented by an irregular quadrangle formed by four points:
  • 2nd left costal cartilage, 0.5 inches (12 mm) from the sternum edge
  • 3rd right costal cartilage, 0.5 inches (12 mm) from the sternum edge
  • 6th right costal cartilage, 0.5 inches (12 mm) from the sternum edge
  • 5th left intercostal space, 3.5 inches (9 cm) from the midline (apex beat).
• Heart Borders:
  • Left border: Primarily the left ventricle (with the left atrium's appendage peeking superiorly); joins points 1 and 4.
  • Lower border: Right ventricle and lower left ventricle; joins points 3 and 4.
  • Right border: Right atrium; joins points 2 and 3.
• Heart Size Estimation: A clenched right fist placed palm-down just below the manubriosternal junction provides a good estimate of the heart's size and position.

Intercostal Arteries and Nerves

• Posterior Intercostal Arteries: Branches of the thoracic aorta (lower nine spaces) or the superior intercostal branch of the costocervical trunk (first two spaces). They run in subcostal grooves and anastomose with anterior intercostal arteries.
• Anterior Intercostal Arteries: Branches of the internal thoracic artery (1st–6th spaces) or its musculophrenic branch (7th–9th spaces). The lowest two spaces are only supplied by posterior arteries.
• Perforating Branches: Piercing the upper five or six intercostal spaces; significant in the female (2nd-4th spaces), supplying the breast.
• Intercostal Nerves: Anterior primary rami of thoracic nerves. Each nerve gives off collateral muscular and lateral/anterior cutaneous branches to innervate the thoracic and abdominal walls.
• Intercostal Nerve Irritation: Can cause referred pain to the front of the chest or abdomen, depending on the peripheral termination of the nerve. This can arise from Pott's disease (tuberculosis) of the thoracic vertebrae.
• Intercostal Nerve Block: A technique for local anesthesia, achieved by infiltration around the intercostal nerve trunk and collateral branch.
• Thoracotomy: Incisions are made along the 5th or 6th rib during surgery (e.g., lobectomy). Protecting the neurovascular bundle and excising the rib allows access to the lung or mediastinum.
• Pus Tracking: Pus from the spine may track along the neurovascular bundles, eventually exiting at points lateral to the erector spinae (sacrospinalis), in the midaxillary line, or just lateral to the sternum.

Diaphragm

• Structure: Dome-shaped muscle separating the thoracic and abdominal cavities. Composed of a peripheral muscular part and a central aponeurosis.
• Muscle Divisions:
  • Vertebral part: From the crura and arcuate ligaments.
    • Right crus: Front of bodies of upper three lumbar vertebrae and intervertebral discs.
    • Left crus: First two lumbar vertebrae.
    • Arcuate ligaments: Fibrous arches (medial, covering psoas major; lateral, covering quadratus lumborum).
  • Costal part: Attached to inner aspect of lower six ribs and costal cartilages.
  • Sternal part: Two small slips from the deep surface of the xiphisternum.
• Central Tendon: Trefoil-shaped, partially fused with the undersurface of the pericardium.
• Innervation: Entirely supplied by the phrenic nerve (C3, C4, C5).
• Diaphragm Paralysis: Characterized by elevation and paradoxical movement (instead of descending on inspiration, it moves upwards due to abdominal pressure).
• Sensory Innervation: Central part: Phrenic nerve; referred pain to the shoulder tip during irritation (e.g., pleurisy or subphrenic collections). Peripheral part: Lower intercostal nerves.
• Congenital Diaphragmatic Hernia: Less common than acquired hernias. May arise through: Foramen of Morgagni, Foramen of Bochdalek, a deficient central tendon, or a large esophageal hiatus.
• Hiatus Hernia (Acquired): Common in middle age, due to weakened or widened esophageal hiatus.
  • Sliding: Upper stomach and lower esophagus slide into the chest during bending or lying down; cardiac incompetency can cause peptic juice regurgitation, leading to issues like esophageal inflammation and strictures.
  • Rolling (Para-esophageal): Fundus of the stomach rolls up through the hiatus in front of the esophagus; may cause epigastric discomfort, flatulence, and dysphagia, but not regurgitation (preserved cardia function).

Respiration Movements

• Inspiration: Increases all thoracic diameters, leading to negative intrapleural pressure and lung expansion.
• Expiration: Relaxation of respiratory muscles and elastic recoil of the lung reduce thorax size and force air out.
• Quiet Inspiration: First rib remains relatively fixed. External and internal intercostals elevate and evert succeeding ribs; this expands the anteroposterior diameter of the thorax (2nd-7th ribs). Lower ribs raise the costal margin, increasing the transverse diameter. The diaphragm's contraction increases the depth.
• Expiration: The relaxation of the ribs and the tone of the abdominal musculature assist in expiration.
• Deep/Forced Respiration: Accessory muscles (e.g., scalenes, sternocleidomastoid, serratus anterior, pectoralis major) are recruited for increased thorax capacity; abdominal muscles aid forced expiration.

Pleurae

• Description: Two separate pleural cavities.
• Structure: Each pleura consists of a visceral layer (lining the lung) and a parietal layer (lining the chest wall, diaphragm, pericardium, and mediastinum).