Overview
This lecture explains the major anatomical structures of the respiratory tract, following the pathway of inspired air from the atmosphere to the alveoli and highlighting key clinical concepts.
Pathway of Air and Major Structures
- Air enters through the nasal cavity or oral cavity.
- Air passes through the pharynx, which consists of nasopharynx, oropharynx, and laryngopharynx.
- The larynx, also known as the voice box, follows the pharynx and contains the vocal cords.
- From the larynx, air moves into the trachea, which is kept open by cartilage for airflow.
- The trachea bifurcates into left and right main stem bronchi.
- Bronchi branch about 23 times, forming smaller bronchioles.
- Bronchioles lead to alveoli, tiny air sacs where gas exchange occurs.
Respiratory Tract Divisions and Clinical Relevance
- The upper respiratory tract includes the nasal cavity, pharynx (all parts), and larynx.
- The lower respiratory tract includes the trachea, bronchi, bronchioles, and lungs (including alveoli).
- Upper respiratory tract infections affect nasal cavity, pharynx, and larynx.
- Lower respiratory tract infections affect trachea, bronchi, bronchioles, and lungs.
Detailed Structure Functions
- Nasal cavity contains turbinates, which warm, humidify, and filter inspired air with mucus and blood vessels.
- Turbinates trap particulates and pathogens before air enters deeper into the tract.
- Right main bronchus is wider and more vertical; inhaled objects are more likely to enter here.
- The right lung has three lobes (superior, middle, inferior); left lung has two lobes (superior, inferior) due to the cardiac notch created by the heart.
- As bronchi branch into bronchioles, cartilage decreases and smooth muscle increases, enabling constriction or relaxation.
- Asthma is a disease of the bronchioles, involving smooth muscle constriction.
Alveoli and Gas Exchange
- Alveoli provide a large surface area (about the size of a tennis court) for gas exchange.
- Oxygen enters the blood from alveoli; carbon dioxide moves from blood into alveoli for expiration.
Key Terms & Definitions
- Pharynx — the throat, divided into nasopharynx, oropharynx, and laryngopharynx.
- Larynx — the voice box containing vocal cords and the laryngeal prominence (Adam’s apple).
- Trachea — the windpipe, reinforced by cartilage to remain open.
- Bronchi — main airway branches from the trachea into each lung.
- Bronchioles — small airway branches with more smooth muscle, less cartilage.
- Alveoli — tiny air sacs in the lungs; main site of gas exchange.
- Turbinates — folded structures in the nasal cavity that filter, humidify, and warm air.
- Cardiac notch — indentation in the left lung for the heart.
- Patent — open, unobstructed airway.
Action Items / Next Steps
- Review anatomical diagrams of the respiratory tract.
- Memorize the sequence of air passage and functions of each structure.
- Study clinical implications of upper vs. lower respiratory tract infections.