U01.16.003 Respiratory Cell Types and Their Functions

Description: Club cells are nonciliated, low-columnar, or cuboidal cells with secretory granules.
Location: Found in the bronchioles.
Functions:
- Degrade toxins in the respiratory tract.
- Secret components of surfactant.
- Serve as reserve cells that can differentiate into other cell types when needed.

Cell Type	Description	Functions
Type I Pneumocytes	Squamous cells that cover 97% of the alveolar surface.	Provide a thin lining for the alveoli, optimizing gas exchange.
Type II Pneumocytes	Cuboidal and clustered cells.	1. Serve as stem cell precursors for both type I and type II pneumocytes, proliferating during lung damage. 2. Secrete surfactant from lamellar bodies, reducing alveolar surface tension and collapse, increasing lung compliance, and decreasing lung recoil.
Alveolar Macrophages	Immune cells within the alveoli.	Phagocytose foreign materials and release cytokines and proteases. May become hemosiderin-laden (“HF cells”) in pulmonary edema or hemorrhage.

Alveolar Cell Types

Surfactant Composition: Composed of multiple lecithins, primarily dipalmitoylphosphatidylcholine (DPPC).
Function:
- Reduces alveolar surface tension.
- Prevents alveolar collapse.
- Decreases lung recoil.
- Increases lung compliance.
Development:
- Surfactant synthesis begins around week 20 of gestation.
- Achieves mature levels by around week 35.
- Corticosteroids play a crucial role in fetal surfactant synthesis and lung development.
Law of Laplace: The collapsing pressure (P) is inversely proportional to the radius of the alveoli, making smaller alveoli more prone to collapse during expiration.

Club cells play a crucial role in detoxifying the bronchioles and maintaining the surfactant balance.
Type I pneumocytes are essential for efficient gas exchange, covering most of the alveolar surface.
Type II pneumocytes are vital for lung repair and surfactant production, which is critical for preventing alveolar collapse.
Alveolar macrophages are key players in the immune defense of the lungs and can indicate underlying pathologies like pulmonary edema or hemorrhage.

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