The pleura

Each lung is enclosed in a double-walled sac referred to as the pleura. The visceral pleura is the membrane adhered to the external surface of the lungs. The parietal pleura lines the walls of the thoracic cavity. The space in between the two layers, the pleural space, is very thin and completely closed. The pleural space is filled with pleural fluid that lubricates the membranes and reduces friction between the layers as they slide past each other during breathing. This fluid also plays a role in maintaining lung inflation. The surface tension between the molecules of the pleural fluid keeps the two layers of the pleura "adhered" to each other — a concept similar to the effect of water between two glass microscope slides. The water molecules pull tightly together and oppose the separation of the slides. In this way, the lungs are in contact with the thoracic wall, fill the thoracic cavity, and remain inflated. In other words, surface tension in the pleural space opposes the tendency of the lungs to collapse.

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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