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Questions and Answers
What is pleura?
A double-walled sac of serous membrane enclosing the lung.
What is the difference between parietal and visceral pleura?
Parietal pleura lines the thoracic cavity, while visceral pleura covers the outer surface of the lung.
What is the function of pleural fluid?
It lubricates the apposing surfaces of the visceral and parietal pleura during respiratory movements.
What is the normal value of pleural fluid?
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What causes negative intrapleural pressure?
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What are the normal values of intrapleural pressure?
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Pleural effusion is a collection of large volume of fluid in the pleural space when the rate of pleural fluid formation exceeds the rate of its _____.
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What type of pneumothorax is defined as an abnormal collection of air in the pleural space?
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Visceral pleura is sensitive to pain, irritation, and inflammation.
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Study Notes
Overview of Pleura
- A double-walled sac of serous membrane enclosing the lungs.
- Comprises two layers: the visceral pleura covers the lung surface, and the parietal pleura lines the thoracic cavity.
Parietal vs. Visceral Pleura
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Parietal Pleura:
- Highly sensitive to pain, irritation, and inflammation.
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Visceral Pleura:
- Generally insensitive to pain and irritation; sensitive only to stretch.
Pleural Cavity
- The narrow space between the visceral and parietal layers.
- Lined by mesothelium, a single layer of cells.
- Contains pleural fluid (5 to 10 mL of clear serous fluid) that lubricates the pleura during respiratory movements.
Composition and Function of Pleural Fluid
- Similar to plasma but lower in protein (< 1.5 g/dl).
- Contains macrophages (75%), lymphocytes, and neutrophils.
- Functions to reduce friction between pleural layers during breathing, allowing smooth lung movement against the chest wall.
Dynamics of Pleural Fluid
- Formation: Occurs via lung interstitial tissue, pleural capillaries, intrathoracic lymphatics, and blood vessels.
- Absorption: Primarily through parietal lymphatics with normal formation and absorption rates at 0.01 mL/kg/h. The capacity for lymphatic clearance is 28 times the normal rate of formation.
Intrapleural Pressure (IPP)
- Refers to the negative pressure in the pleural cavity.
- Caused by a lack of air and the lung's tendency to recoil due to elasticity, countering the chest wall's expansion.
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Normal Values:
- -3 mmHg at the end of normal expiration.
- -6 mmHg at the end of normal inspiration.
- -30 mmHg during forced inspiration (Muller's experiment).
- +40 mmHg during forced expiration (Valsalva's maneuver).
Significance of Negative Intrapleural Pressure
- Allows lung expansion during inspiration and prevents collapse during expiration.
- Facilitates venous return to the heart.
- Aids in lymphatic drainage.
Conditions Related to Pleura
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Pneumothorax:
- Abnormal air collection in the pleural space.
- Symptoms include sudden chest pain and shortness of breath.
- Can occur spontaneously or due to trauma.
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Pleural Effusion:
- Excess fluid in the pleural space due to formation exceeding absorption.
- Classified as:
- Transudate: Low protein, caused by increased capillary pressure or decreased plasma proteins (e.g., cardiac failure, liver cirrhosis).
- Exudate: High protein, resulting from increased capillary permeability (e.g., pneumonia, inflammation).
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Description
Test your knowledge on the physiology of pleura with this quiz. Explore key concepts such as the differences between parietal and visceral pleura, the role of intrapleural fluid, and the significance of intrapleural pressure. Enhance your understanding of this essential anatomical structure.
