The lungs are the essential organs of respiration; they are two in number and are placed one on either side within the thorax, separated from each other by the heart. The substance of the lung is light, spongy and porous. The surface is smooth, shining and marked into numerous areas, indicating the lobules of the organs (Lewis, 2000). 2. Gross anatomy of the lungs
The lungs are situated into the thoracic cavity, which are divided into three large spaces: the mediastinum, and the two pleural cavities (Gilroy, MacPherson, Ross & Schuenke, 2008). The mediastinum is an interpleural space (area between the pleural cavities) in the thorax and it consists of the superior mediastinum above the pericardium and the three lower divisions: anterior, middle and posterior (Chung, 2007). The lungs and the surface of the pleural cavities are lined by a single flat layer of cells called the pleural membrane (Drake, Vogl, Mitchell & Gray, 2005). Fluid between the layers prevents friction with the cavity’s inner wall as the lungs repeatedly expand and contract. The pleura is divided into two major types, based on location: parietal pleura (associated with the walls of a pleural cavity) and visceral pleura (adheres to and covers the lungs) (Drake et al., 2005). The visceral pleura, lines the inner wall of the pleural cavity; covers the lobes and root of the lung (Leonard, 1995) However, the inner surfaces of the cavities (parietal pleura) are divided into four parts depending on its location: costal, diaphragmatic, mediastinal and cervical (see figure 1) (Clemente, 2006). Surfaces
The lung has three surfaces: a convex surface abutting the rib cage, more sharply curved posteriorly than anteriorly; a concave mediastinal surface, and a concave diaphragmatic surface conforming to the convexity of the diaphragm as it covers the domes of the liver and spleen. (Thurlbeck & Churg, 2005). [pic]
Figure1: Schematic representation of the most important features of the lungs, including the apex, lobes, fissures, bronchi, bronchioles and alveoli. (Davis, M.K. (2009).An overview of the respiratory system. Retrieved June 18, 2010, from www.drtummy.com.) 2.1 Main features of the left and right lung (see figure 1) The apex of the lungs is rounded, and extends through the superior thoracic aperture into the root of the neck, reaching 2.5 to 4 cm above the level of the sternal end of the first rib. The apex of the lung is crossed by the subclavian artery, which produces a groove in the mediastinal surface.(Lewis, 2000) The base of the lung is broad, concave and its diaphragmatic surface, rests upon the diaphragm which separates the right lung from the right lobe of the liver, and the left lung from the left lobe of the liver, the stomach and the spleen (Kahle, Leonhard & Platzer, 1993). The base of the right lung is deeper since the diaphragm extends higher on the right than on the left side. The hilum is where the root is attached to the lung. It is the location at which the bronchi and neurovascular structure connect the lung (Gilroy et al.,2008) The lungs contain impressions. For example, the heart produces deep impressions anterior to the hilum of each lung, being especially pronounced on the left. Each lung presents anterior, posterior and inferior borders. The borders tend to divide the lung into lateral, medial and inferior surfaces. The right lung is composed of three lobes (the upper, middle and lower) and is the larger of the two lungs. The left is made up only of two lobes, the upper and the lower. Two fissures are present on the right. The oblique fissure separates the lower lobe from the upper and middle lobes, and the horizontal fissure separates the other two. On occasion, such fissures are visible as linear shadows on the radiograph of the chest, and the...