Pulmonary System Overview

Introduction to Pulmonary Anatomy and Physiology

The pulmonary system is responsible for gas exchange, ventilation, and regulation of blood gases. Understanding its structure and function is essential for recognizing how diseases can impact respiratory health.

• Ventilation: The process of moving air into and out of the lungs.

• Gas Exchange: The transfer of oxygen (O2) and carbon dioxide (CO2) between the lungs and blood.

• Regulation: The control of blood pH and gas concentrations through respiratory activity.

Anatomy of the Pulmonary System

Major Structures

• Nasal Cavity: Warms, moistens, and filters incoming air.

• Pharynx: Passageway for air and food; connects nasal cavity to larynx.

• Larynx: Contains vocal cords; routes air and food into proper channels.

• Trachea: Windpipe; conducts air to the bronchi.

• Bronchi: Main passageways into the lungs.

• Lungs: Main organs of respiration, containing bronchi, bronchioles, and alveoli.

Bronchial Tree

The bronchial tree is a branching system of airways that conducts air from the trachea to the alveoli.

1. Extrapulmonary Bronchi: Main bronchi outside the lungs.

2. Intrapulmonary Bronchi: Bronchi within the lungs.

3. Large/Primary Bronchi: First branches from the trachea.

4. Terminal Bronchioles: Smallest bronchioles without alveoli attached.

5. Respiratory Bronchioles: Bronchioles with some alveoli in their walls.

6. Alveolar Ducts: Ducts leading to clusters of alveoli.

7. Alveolar Sacs: Clusters of alveoli where gas exchange occurs.

Microscopic Structure of the Lungs

• Alveoli: Tiny air sacs where gas exchange occurs; surrounded by capillaries.

• Alveolar Ducts and Sacs: Terminal ends of the respiratory tree, composed of clusters of alveoli.

Example: The human lung contains millions of alveoli, providing a large surface area for efficient gas exchange.

Cell Types in the Alveoli

Alveolar Cell Types and Functions

• Type I Alveolar Cells: Thin, simple squamous epithelial cells; cover about 95% of the alveolar surface and are responsible for gas exchange via passive diffusion.

• Type II Alveolar Cells: Cuboidal cells that synthesize and secrete pulmonary surfactant, reducing surface tension and preventing alveolar collapse.

• Alveolar Macrophages: Immune cells that clean the alveoli by phagocytosing debris and pathogens.

Additional info: Surfactant is critical for reducing the work of breathing, especially in newborns.