Art of Physiology

The Lungs Together – The Shape of a Bell
The chest quietly expands and contracts under basal conditions in order to serve the alveoli. At first glance it seems like a simple bellows-like process, but as one delves into the layers of detail, the complexity of the structural design unfolds as a combination of physical and chemical forces.
 
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The inspiratory capacity (IC) is the total volume that the person can inspire, and is a combination of the inspiratory component of the tidal volume and the inspiratory reserve volume.
Courtesy of: Ashley Davidoff, M.D. TheCommonVein.net
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The Alveolus – The Centre of the Pulmonary Universe
The five major layers that keep the air moving include the outer bony cage, the muscular layer represented in maroon, the pleural complex (orange yellow orange) the lung (blue) and surfactant within the alveolus. (pink)
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Ashley Davidoff MD TheCommonVein.net
The first of five functional layers consists of the bony skeleton consisting of the sternum and the spine, which are fixed, and the ribs that move up and outward on inspiration and down and inward on expiration.
Courtesy of: Ashley Davidoff, M.D. TheCommonVein.net
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The lungs – as they live and breathe
The chest is surrounded by a ring of muscle (maroon) made up of a various groups which work in concert. The diaphragm is the workhorse of the respiratory muscles and is shown as a thick maroon band inferiorly. Ashley Davidoff MD  TheCommonVein.net 42530b05b09b14
The two layers of pleura (orange) are held together by a thin layer of pleural fluid (yellow) by cohesive and adhesive forces. The visceral pleura is connected to the lung while the parietal pleura is attached to the chest wall. The pleura and fluid as a unit bind the chest wall to the lungs. The cohesion and adhesion that results keeps the outer chest cage of bone and muscle in intimate contact with the lungs, being pulled and pushed together in the harmonious dance of respiratory movement.
Ashley Davidoff, M.D.
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CT scan of the Diaphragm in Coronal Plain (above) and Cross Section (below)
The diaphragm plays the most important role in breathing. Although it covers a large area it is relatively thin and therefore it usually cannot be fully appreciated on axial cuts. Can you see the diaphragm in this coronal image, and if so why is it so well seen? Additionally why do you think it does not continue all the way across the midline?
The reason we see the diaphragm so well is because there is fluid in both the chest cavity and abdominal cavity and the interface of fluid density on the contrasting soft tissue density of the diaphragm makes it more easily discernible. The central part of the diaphragm is called the central tendon of the diaphragm and it is in continuity with the pericardium. True to its name it is tendinous and therefore very thin and difficult to image.
In this cross sectional image of the same patient the diaphragm is seen as an undulating thin muscle. Since it is dome shaped with its attachments inferiorly only parts in this particular cross section are seemingly attached to the ribs. The undulations are caused by tendinous attachments that extend from the ribs to the central tendon. The full diaphragm was not visualized in this patient and the digitally manipulated image has interpolated the data to provide a circumferential view.
Ashley Davidoff MD TheCommonVein.net 42557b04c