Pulmonary System Lecture

Anatomy of the Lungs

Right Lung

• 3 lobes
• Further subdivided into 9-10 segments

Left Lung

• 2 lobes
• Further subdivided into about 8 segments

Lung Segments

• Can be individually removed in case of disease (e.g., cancer)

Lung Structure

• Apex: Pointed tip
• Base: Sits on the diaphragm
• Hilum: Entry/exit point for blood vessels and bronchi
  • Pulmonary vein exits
  • Pulmonary artery enters
  • Bronchus enters
  • Lymphatic capillaries also enter and exit

Blood Supply

Pulmonary Circulation

• Pulmonary trunk carries deoxygenated blood from the right ventricle to the lungs
• Pulmonary veins bring oxygenated blood from the lungs back to the left atrium

Bronchial Circulation

• Bronchial arteries arise from the descending aorta
• Enter the lungs at the hilum
• Supply oxygenated blood to the lung tissues
• Bronchial veins join with pulmonary veins

Pleura

• Double serous membrane
  • Parietal Pleura: Lines inner surface of thoracic cavity
  • Visceral Pleura: Attaches directly to lung surface
• Pleural Cavity: Space between parietal and visceral pleura; contains pleural fluid

Respiratory Physiology

Pulmonary Ventilation

• Inhalation (Inspiration): Breathing in
• Exhalation (Expiration): Breathing out
• Volume changes in the thoracic cavity lead to pressure changes, driving airflow

Pressure Relationships

• Atmospheric Pressure: 760 mm Hg at sea level (1 atm)
• Negative Respiratory Pressure: Lower than atmospheric pressure
• Positive Respiratory Pressure: Higher than atmospheric pressure
• Zero Respiratory Pressure: Equal to atmospheric pressure

Intrapulmonary Pressure

• Pressure within alveoli
• Fluctuates with breathing, eventually equalizes with atmospheric pressure (~760 mm Hg or 0 mm Hg)

Intrapleural Pressure

• Pressure within pleural cavity
• Fluctuates with breathing, always negative (~756 mm Hg or -4 mm Hg)

Transpulmonary Pressure

• Difference between intrapulmonary and intrapleural pressure
• Higher transpulmonary pressure indicates larger lung volume

Lung Collapse (Atelectasis)

• Caused by blocked bronchioles (e.g., pneumonia) or pneumothorax (air in pleural cavity)
• Pneumothorax can be due to injury to parietal pleura or rupture of visceral pleura
• Treated by removing air with chest tubes

Pulmonary Ventilation Mechanism

Boyle's Law

• Relationship between pressure and volume (P ∝ 1/V)
• Volume increases → Pressure decreases
• Volume decreases → Pressure increases

Inspiration (Inhalation)

• Active process
• Diaphragm contracts (flattens)
• External intercostal muscles contract (ribcage rises)
• Thoracic cavity volume increases
• Intrapulmonary pressure drops (~759 mm Hg)
• Air flows in from high to low pressure
• Forced inspiration: Accessory muscles further increase thoracic volume (during exercise or COPD)

Expiration (Exhalation)

• Passive process
• Inspiratory muscles relax (diaphragm becomes dome-shaped, ribcage lowers)
• Thoracic cavity volume decreases
• Intrapulmonary pressure rises (~761 mm Hg)
• Air flows out from high to low pressure

Key Concepts

• Intrapulmonary pressure: Balanced with atmospheric pressure during regular breathing
• Intrapleural pressure: Always negative, crucial to avoid lung collapse
• Transpulmonary pressure: Indicates lung volume and health