Overview
This lecture covers lung anatomy, physiology, function, pathophysiology, and related diseases, with a focus on mechanisms of breathing, gas exchange, and pulmonary function testing.
Lung Structure and Anatomy
- The lungs are divided into upper (pharynx, larynx) and lower (trachea, bronchi, bronchioles, alveoli) respiratory tracts.
- Alveoli are the primary sites of gas exchange and have two cell types: type I (gas exchange) and type II (surfactant production).
- The lungs are enveloped by visceral and parietal pleura, with pleural fluid reducing friction during breathing.
Physiology of Breathing
- Breathing is driven by diaphragm contraction (via phrenic nerve); intercostal muscles assist in chest expansion.
- Inspiration creates negative pressure in the lungs, drawing air in; expiration is passive due to elastic recoil.
- Compliance (stretchability) and airway resistance are key in lung mechanics; diseases often affect one or both.
Gas Exchange
- Oxygen and carbon dioxide move across alveolar membranes by simple diffusion, driven by pressure gradients.
- Hemoglobin binds oxygen (up to four molecules), with saturation depicted by the oxygen-hemoglobin dissociation curve.
- Oxygen levels and blood pH can affect hemoglobin’s oxygen affinity.
Pulmonary Function Testing
- Pulmonary function tests (PFTs), including spirometry, measure lung volumes like FEV1 (forced expiratory volume in 1 second) and FVC (forced vital capacity).
- COPD shows reduced FEV1/FVC ratio, increased residual volume; asthma can have normal or reduced FEV1.
Lung Diseases and Disorders
- COPD includes emphysema (increased compliance, air trapping) and chronic bronchitis (cough, mucus, gas exchange issues).
- Alpha-1 antitrypsin deficiency (autosomal recessive) reduces lung protection from proteases.
- Asthma is a chronic inflammatory airway disease with reversible obstruction, wheezing, and episodic attacks.
- Interstitial lung diseases (e.g., fibrosis) reduce lung compliance; pulmonary vascular disorders include embolism, edema, and hypertension.
Immune Function and Other Considerations
- Goblet cells secrete mucus; ciliated epithelial cells help clear debris.
- Cystic fibrosis (autosomal recessive) impairs chloride transport, leading to thick mucus.
- Lungs are sensitive to pollutants; immune defenses include mucociliary clearance, IgA, macrophages, and neutrophil proteases.
Neurologic and Mechanical Regulation of Breathing
- Breathing is controlled by the brainstem’s pre-Bötzinger complex; can be consciously overridden.
- Neural, emotional, and metabolic signals modify respiratory patterns.
Surfactant
- Surfactant, produced by type II alveolar cells, reduces surface tension, preventing alveolar collapse and assisting lung compliance.
Key Terms & Definitions
- Alveoli — Tiny air sacs for gas exchange.
- Compliance — Lung's ability to stretch and expand.
- FEV1 — Volume of air forcibly exhaled in one second.
- Surfactant — Substance reducing alveolar surface tension.
- Asthma — Chronic inflammatory airway disease.
- COPD — Group of diseases with airflow obstruction.
- Simple diffusion — Passive movement of gases down a concentration gradient.
- Alpha-1 antitrypsin — Protein protecting lungs from protease damage.
Action Items / Next Steps
- Read designated textbook pages: 79 (diffusion), 406 (lung pressures), 412 (surfactant), 422–423 (hemoglobin saturation).
- Review pulmonary function test graphs and oxygen dissociation curves.
- Watch provided COVID-19 lung impact video; study Figure 1127 (page 425).
- Prepare and email questions on assigned readings before next class.
- Review genetic inheritance patterns for lung-related disorders.