Pleural Cavity and Layers of Pleura

Study Notes

Pleural Effusion

The pleura consists of two layers: parietal pleura (covers chest wall, diaphragm, and mediastinum) and visceral pleura (covers lungs, including interlobar fissures).
The two layers are separated by a virtual cavity containing 5-10 mL of fluid.

Pleural Liquid Turnover

Pleural liquid originates from systemic vessels of both parietal and visceral pleural membranes.
Parietal vessels are more important due to proximity to the pleural space and higher filtration pressure.
Pleural liquid is partially reabsorbed by microvessels, with remaining fluid exiting via lymphatic stomata in the parietal pleura.

Pathways to Pleural Effusion

Increased fluid entry:
- Increased microvascular pressure (elevated venous pressure, CHF, pulmonary embolism, central venous obstruction)
- Increased permeability (inflammation, infection, malignancy)
- Decreased pleural pressure (atelectasis)
- Decreased plasma osmotic pressure (hypoalbuminemia)
Decreased fluid exit:
- Intrinsic factors: cytokines, endocrine abnormalities, radiation/drug injury, cancer infiltration, anatomic abnormalities
- Extrinsic factors: limited respiratory motion, mechanical compression, decreased intrapleural pressure, increased systemic venous pressure

Determining the Cause of Pleural Effusion

Thoracentesis with imaging guidance is a simple bedside procedure for rapid fluid sampling and analysis.
Analysis of pleural fluid helps determine the cause of the effusion.

Indications for Thoracentesis

Diagnostic: most patients with newly detected pleural effusion should undergo diagnostic thoracentesis to determine the nature of the effusion and identify potential causes.
Therapeutic: performed for symptom relief, complicated pleural effusions, and pleural conditions at risk of thickening and functional impairment.

Description

Learn about the anatomy and physiology of the pleural cavity, including the parietal and visceral pleura, and their blood supply and sensory nerve distribution. Understand the structure and function of the pleura and its importance in the respiratory system.