ANATOMY OF THE PLEURA

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In humans, all vital organs are protected within a body wall formed by ribs, vertebrae, and layers of thick muscle. Within the confined spaces vital organs such as the heart and lung, however, have to move and change volume continuously to function. For the best protection and function of the lung, the thoracic cage is shaped like a bellows with the diaphragm as the moving part. Moreover, the outer surface of the lung and the inner surface of the thoracic cage are covered by an elastic serous membrane with a smooth and lubricating surface to form a pleural cavity. This is almost like inserting a sealed wet and stretchable plastic bag between the lung and the thoracic wall to decrease friction.

Thus, the pleura and pleural cavity are essential for the efficient function of the lung, as are the pericardium and pericardial cavity for the heart. This arrangement is so important that in the embryo, a body cavity lined by a serous membrane is formed, and the measures needed to maintain the cavity open are implemented before the vital organs develop.

Section snippets

EMBRYOLOGY

In the human embryo, the primitive mesoderm on both sides of the notochord divides first into the medial segmented and lateral nonsegmented plates. The medial segmented plates later develop into the protecting skull and vertebrae around the brain and spinal cord, and the ribs and thick muscles of the dorsal body wall.

The lateral nonsegmented plates, on the other hand, split into an internal splanchnopleure (the precursor of organs) and a lateral somatopleure (the precursor of the body wall) to

THE KAMPMEIER'S FOCI

As early as 1928, Kampmeier discovered small milky spots in the dorsal and caudal portion of the mediastinum in rats and humans.8 By scanning electron microscopy, they appear as irregularly elevated mound-like structures.42 This focus is covered by cuboidal mesothelial cells with stomas and has an aggregate of lymphocytes, histiocytes, plasma cells, and other mononuclear cells around central lymphatic or vascular vessels. Similar foci were later found in the lower thoracic cavity of the dog and

SUMMARY

The lung and heart, the vital organs, have to be protected and also have to move and change volume continuously to function. For the best protection and function of the lung, the thorax is shaped almost like a bellows with the diaphragm as the moving part. Furthermore, the outer surface of the lung and the inner surface of the protective thoracic cage are covered by an elastic, serous, and lubricating membrane to form the pleural cavity. This is almost like inserting a sealed-wet and

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    Address reprint requests to Nai-San Wang, MD, PhD, Dean's Office, College of Medicine, National Cheng Kung University, 1 Ta Hsueh Road, Tainan, Taiwan 70101

    *

    National Cheng Kung University Hospital, College of Medicine, National Cheng Kung University, Tainan, Taiwan

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