Overview
This lecture introduces the respiratory system, covering its functions, anatomy, histology, defense mechanisms, and related diseases, as well as the mechanics of breathing.
Functions of the Respiratory System
- Supplies oxygen for cellular respiration (ATP production) and eliminates carbon dioxide, a waste product.
- Pulmonary ventilation refers to air movement in and out of the lungs.
- Responsible for olfaction (smell) and vocalization (speech).
- Closely connected to the cardiovascular system for gas exchange.
Anatomy of the Respiratory System
- Divided into upper (nose, nasal cavity, paranasal sinuses, nasopharynx) and lower (larynx, trachea, bronchi, bronchioles) components.
- Right lung is larger (3 lobes) than the left (2 lobes) due to the heart's position (cardiac notch).
- Lungs have costal (ribs), mediastinal (heart), and diaphragmatic (diaphragm) surfaces.
- Lungs are elastic and held inflated by the pleura (visceral and parietal layers) and pleural fluid.
Conducting and Respiratory Zones
- Conducting zone: moves, cleans, warms, and humidifies air (nasal cavity through bronchioles).
- Respiratory zone: site of gas exchange (alveolar sacs/alveoli).
- Respiratory epithelium changes from ciliated pseudostratified columnar to stratified squamous in areas exposed to abrasion (oropharynx, laryngopharynx).
Airway Histology & Defense
- Ciliated mucous membrane traps debris/pathogens; cilia move mucus toward the throat.
- Nasal vestibule hairs filter large particles.
- Nasal conchae create turbulence, aiding in air cleaning, warming, humidifying, and odor detection.
- Hard and soft palates separate nasal and oral cavities.
Larynx, Trachea, and Bronchial Tree
- Larynx (voice box) contains vocal cords (true and false); muscles control pitch and sound.
- Epiglottis prevents food from entering the trachea during swallowing.
- Trachea has C-shaped hyaline cartilage rings and is anterior to the esophagus; muscle (trachealis) adjusts airway diameter.
- Carina is sensitive and triggers coughing.
- Right main bronchus is wider and steeper than the left, so aspirated objects typically enter the right lung.
- Bronchial tree branches into bronchioles and eventually alveolar sacs (site of gas exchange).
Alveoli and Gas Exchange
- Alveoli are lined with type 1 cells (simple squamous epithelium) and type 2 cells (produce surfactant to reduce surface tension).
- Surrounded by elastic fibers and capillaries for efficient gas exchange.
- Macrophages in alveoli engulf pathogens and debris.
Respiratory Diseases
- Emphysema: chronic, irreversible alveolar sac degeneration, often from smoking or pollution.
- Chronic bronchitis: persistent inflammation of bronchi, leads to mucus buildup and coughing.
- Asthma: airway smooth muscle constriction and inflammation, causing narrowed airways and breathing difficulty.
Breathing Mechanics
- Diaphragm and intercostal muscles contract to inhale (increase chest volume, decrease pressure, air in).
- Relaxation of these muscles causes exhalation (decrease chest volume, increase pressure, air out).
Key Terms & Definitions
- Pulmonary ventilation — movement of air into and out of the lungs.
- Pleura — double-layered membrane surrounding each lung.
- Alveoli — tiny air sacs for gas exchange.
- Surfactant — detergent-like substance reducing alveolar surface tension.
- Type 1 alveolar cells — squamous epithelial cells in alveoli for gas exchange.
- Type 2 alveolar cells — cells that secrete surfactant.
- Carina — the tracheal bifurcation sensitive to irritants (triggers cough reflex).
Action Items / Next Steps
- Review anatomical diagrams of the respiratory system.
- Understand the difference between the conducting and respiratory zones.
- Be prepared to define and identify major structures and their functions.