The factors responsible for holding the lungs to the thorax wall are surface tension from pleural fluid and negative pressure in the pleural cavity.

This article will provide an overview of how the lungs and thorax wall are held together, as well as the role of surface tension and negative pressure in keeping the lungs in place.

Lungs

The lungs are the primary organs of the respiratory system that are responsible for gas exchange. They are located beneath the sternum within the thoracic cavity and are separated by the mediastinum.

The right lung is slightly larger than the left lung and has three lobes, while the left has only two. Each lobe is further divided into bronchopulmonary segments, which branch off into tiny air sacs known as alveoli.

This is where the exchange of oxygen and carbon dioxide takes place.

The lungs work by expanding and contracting to allow air to enter and exit during a breathing cycle. When the lungs expand, they create negative pressure in the pleural cavity, which sucks the lungs back towards the thoracic wall.

Thoracic Cavity

The thoracic cavity is a space in the body that is enclosed by the ribs, sternum, and vertebral column. It contains the heart, lungs, and other organs of the respiratory and circulatory systems.

The thoracic cavity is divided into two compartments:

  1. Pleural cavity
  2. Mediastinum

Pleural Cavity

The pleural cavity is a space between the lungs and the thoracic wall. It is lined by the pleura, a double-layered membrane that consists of the visceral pleura and parietal pleura.

The visceral pleura covers the surface of the lungs and is attached to the lung tissue. The parietal pleura lines the thoracic wall and is attached to the ribs.

The pleural cavity contains a small amount of pleural fluid, which lubricates and protects the lungs. This fluid also reduces friction between the pleura during breathing.

Mediastinum

The mediastinum is the central region of the thoracic cavity that contains several structures, including the following:

  • Heart
  • Blood vessels
  • Esophagus
  • Trachea
  • Nerves
  • Thymus
  • Thoracic duct
  • Lymph nodes

The mediastinum is surrounded by loose connective tissue and divided into superior and inferior compartments.

What is the Thoracic Wall?

The thoracic wall is the structure that encloses the thoracic cavity. It consists of the ribs, sternum, and vertebral column.

The ribs are attached to the vertebral column in the back and the sternum in the front. They form a cage that protects the organs of the thoracic cavity.

The sternum is a long, flat bone that is located in the center of the thoracic cavity. It articulates with the ribs and forms the sternocostal joints.

thorax wall labeled

What Holds the Lungs to the Thorax Wall?

As previously mentioned, the lungs are held to the thorax wall by:

  1. Surface tension from pleural fluid
  2. Negative pressure in the pleural cavity

Surface Tension

Surface tension is the force that keeps the pleura together and prevents the lungs from collapsing. It is created by the attraction of water molecules to each other.

Pleural fluid is a lubricating and protective fluid that is produced by the pleura. It contains water, electrolytes, and proteins.

The surface tension of the pleural fluid creates a film that coats the lungs and thoracic cavity. This film prevents the lungs from collapsing and allows them to expand and contract during breathing.

Negative Pressure

The negative pressure in the pleural cavity is created by the expansion of the lungs during inhalation. This pressure forces the lungs back towards the thoracic wall and keeps them in place.

The negative pressure also prevents air from entering the pleural cavity during exhalation. If air were to enter the pleural cavity, it would collapse the lungs.

This is known as a pneumothorax.

The negative pressure in the pleural cavity is created by the respiratory muscles, which contract and expand the lungs. These muscles include the diaphragm, intercostal muscles, and scalene muscles.

What is Pulmonary Surfactant?

Pulmonary surfactant is a lipoprotein that is produced by the alveoli of the lungs. It coats the inside of the alveoli and prevents them from collapsing.

Pulmonary surfactant is essential for breathing and is responsible for keeping the alveoli open. It is also responsible for reducing the surface tension of the pleural fluid.

What is Lung Compliance?

Lung compliance is the ability of the lungs to expand and contract during breathing. It is determined by the elasticity of the lung tissue and the surface tension of the pleural fluid.

Lung compliance is increased by pulmonary surfactant and decreased by inflammation of the lung tissue.

Final Thoughts

The factors that are responsible for holding the lungs to the thorax wall are surface tension from pleural fluid and negative pressure in the pleural cavity. Pulmonary surfactant also plays a role in keeping the lungs inflated by reducing the surface tension of the pleural fluid.

Lung compliance is determined by the elasticity of the lung tissue and the surface tension of the pleural fluid. The factors that contribute to lung compliance are pulmonary surfactant and inflammation of the lung tissue.

Be sure to check out our full guide on the pleural diseases that can affect the lungs and structures of the thoracic cavity. Thanks for reading!

Written by:

John Landry, BS, RRT

John Landry is a registered respiratory therapist from Memphis, TN, and has a bachelor's degree in kinesiology. He enjoys using evidence-based research to help others breathe easier and live a healthier life.

References

  • Egan’s Fundamentals of Respiratory Care. 12th ed., Mosby, 2020.
  • Cardiopulmonary Anatomy & Physiology: Essentials of Respiratory Care. 7th ed., Cengage Learning, 2019.
  • Hussain, Azhar, and Bracken Burns. “Anatomy, Thorax, Wall.” National Library of Medicine, StatPearls Publishing, Jan. 2022, www.ncbi.nlm.nih.gov/books/NBK535414

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Medical Disclaimer: The information provided by Respiratory Therapy Zone is for educational and informational purposes only. It should not be used as a substitute for professional medical advice, diagnosis, or treatment. Please consult with a physician with any questions that you may have regarding a medical condition.