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The left and right lungs (Figure 23-7a, b) are situated in the left and right pleural cavities. Each lung is a blunt cone, with the tip, or apex, pointing superiorly. The apex on each side extends into the base of the neck superior to the first rib. The broad concave inferior portion, or base, of each lung rests on the superior surface of the diaphragm.
Lobes and Surfaces of the Lungs
The lungs have distinct lobes separated by deep fissures (Figures 23-7a,b). The right lung has three lobes: superior, middle, and inferior, separated by the horizontal and oblique fissures. The left lung has only two lobes: superior and inferior, separated by the oblique fissure. The right lung is broader than the left, because most of the heart and great vessels project into the left thoracic cavity. However, the left lung is longer than the right lung, because the diaphragm rises on the right side to accommodate the mass of the liver. The curving anterior portion of the lung that follows the inner contours of the rib cage is the costal surface. The mediastinal surface, containing the hilus, has a more irregular shape. The mediastinal surfaces of both lungs bear grooves that mark the passage of the great vessels and of the cardiac impressions, concavities that conform to the shape of the pericardium (Figures 23-7a,b and 23-8). The cardiac impression of the left lung is deeper than that of the right lung. In anterior view, the medial edge of the right lung forms a vertical line, whereas the margin of the left lung is indented at the cardiac notch.
Alveolar Ducts and Alveoli
Respiratory bronchioles are connected to individual alveoli and to multiple alveoli along regions called alveolar ducts (Figures 23-10b). These passageways end at alveolar sacs, common chambers connected to multiple...
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