Unit
- Upper airway structures: The nasal cavity, pharynx, and larynx filter, warm, and humidify inspired air. The nasal cavity contains turbinates that increase surface area for conditioning air. The pharynx serves as a common passage for air and food, while the larynx houses the vocal cords and prevents aspiration during swallowing.
- Lower airway anatomy: The trachea bifurcates into right and left mainstem bronchi at the carina, located at the level of the sternal angle. The right mainstem bronchus is wider, shorter, and more vertical, making it a common site for aspiration of foreign objects. The bronchi divide into smaller bronchioles, leading to respiratory bronchioles and alveolar ducts.
- Alveolar structure and function: Alveoli are thin-walled sacs surrounded by pulmonary capillaries where gas exchange occurs. Type I pneumocytes form the majority of the alveolar surface area and facilitate diffusion. Type II pneumocytes produce surfactant, a lipoprotein that reduces surface tension and prevents alveolar collapse at end-expiration.
- Pleural membranes: The visceral pleura covers the lung surface, and the parietal pleura lines the chest wall. The pleural space between them contains a thin layer of fluid that lubricates movement and creates negative pressure to keep lungs inflated during inspiration.
- Thoracic cage mechanics: The rib cage, sternum, and thoracic vertebrae form a protective framework. The diaphragm is the primary muscle of inspiration; when it contracts, it flattens and increases thoracic volume. External intercostal muscles elevate the ribs during quiet breathing, while accessory muscles aid during increased demand.
- Pulmonary circulation: Deoxygenated blood travels from the right ventricle through the pulmonary arteries to the alveolar capillaries. Oxygenated blood returns via pulmonary veins to the left atrium. This circuit operates at lower pressure than systemic circulation to prevent fluid leakage into the alveoli.
- Innervation and control of breathing: The respiratory center in the medulla oblongata sets the rhythm of ventilation. Central chemoreceptors in the brainstem respond to changes in carbon dioxide levels via cerebrospinal fluid pH. Peripheral chemoreceptors in the carotid and aortic bodies sense oxygen, carbon dioxide, and pH changes.
- Mucociliary clearance: Ciliated epithelial cells line the airways from the trachea to terminal bronchioles. Mucus secreted by goblet cells traps inhaled particles. Cilia beat in a coordinated fashion to move mucus upward toward the pharynx, where it is swallowed or expectorated. Smoking impairs this mechanism.
- Lung volumes and capacities: Tidal volume is the amount of air moved in and out during quiet breathing. Inspiratory reserve volume and expiratory reserve volume are additional amounts that can be inhaled or exhaled. Vital capacity is the sum of tidal volume, inspiratory reserve, and expiratory reserve volumes. Residual volume remains in the lungs after maximal expiration to prevent collapse.
- Ventilation perfusion matching: Efficient gas exchange depends on matching alveolar ventilation with pulmonary blood flow. In healthy lungs, gravity causes regional differences: dependent zones receive more blood flow and ventilation. Hypoxic pulmonary vasoconstriction redirects blood from poorly ventilated areas to optimize oxygenation. Mismatch leads to shunt or dead space effects.
Scope of Practice
Role: Respiratory Therapy Department Coordinator
Within scope:
- Facilitating patient education on basic anatomy and breathing techniques.
- Coordinating diagnostic scheduling and ensuring equipment availability.
- Documenting patient history related to respiratory symptoms.
Outside scope:
- Performing physical assessment of lung sounds or chest palpation.
- Interpreting diagnostic imaging such as chest X-rays.
- Prescribing oxygen therapy or medication.
Quick Revision
- The respiratory system comprises upper and lower airways, alveoli, and pleural membranes.
- Gas exchange occurs across the alveolar-capillary membrane via diffusion.
- The diaphragm is the primary inspiratory muscle, supported by intercostal muscles.
- Breathing is controlled by the medulla oblongata with input from chemoreceptors.
- Mucociliary clearance protects the lungs from inhaled pathogens and debris.