Lungs - gross anatomy

The lungs are paired respiratory organs located in the thoracic cavity, enclosed in the pleural sac. The right lung weighs approximately 700g and the left 650g. In newborns, lungs are rosy pink, becoming dark brown or black in adults due to inhaled carbon particles. Adult lungs are spongy, porous, highly elastic, crepitate on touch (due to air in alveoli), and float in water. Fetal or stillborn lungs are solid, do not crepitate, and sink in water, a distinction useful in forensic medicine.

Each lung is conical, featuring an apex, a base, three borders (anterior, posterior, inferior), and two surfaces (costal and medial). Side determination is crucial: the apex points upwards, the large convex costal surface faces outwards, and the anterior border is sharp and short, while the posterior is thick and rounded. It's important to note that lobe number is not a reliable indicator for side determination, as variations exist.

The apex is blunt, points upwards, covered by cervical pleura, and extends above the first rib and clavicle. It has an impression for the subclavian artery. The base is concave, resting on the diaphragm, with more concavity on the right due to the liver. It's also known as the diaphragmatic surface. The anterior border is thin, sharp, and vertical, with a cardiac notch and lingula on the left lung. The posterior border is thick, rounded, ill-defined, and extends from C7 to T10. The inferior border is semilunar, separating the base from the costal surface.

The costal surface is large, smooth, and convex, relating to ribs and intercostal spaces. The medial surface is divided into a posterior vertebral part (related to vertebrae and intercostal vessels) and a larger anterior mediastinal part, which attaches to the hilum. The mediastinal surface shows various impressions differing between the right and left lungs. The right lung has impressions of the right atrium, superior vena cava, inferior vena cava, azygos vein arch, trachea, and esophagus. The left lung shows impressions of the left ventricle, ascending aorta, aortic arch, descending aorta, left common carotid artery, left subclavian artery, trachea, and esophagus, along with nerves and veins.

The right lung commonly has three lobes (upper, middle, lower) divided by an oblique and a horizontal fissure. The oblique fissure starts 6.5 cm below the apex on the posterior border and reaches the inferior border 7 cm lateral to the midline. The horizontal fissure starts from the oblique fissure at the mid-axillary line and extends to the anterior border, separating the middle lobe. The left lung usually has two lobes (upper and lower) separated by only one oblique fissure. Fissures play a role in lung expansion during respiration and are visible in chest X-rays.

The root of the lung is a short pedicle connecting the lung to the mediastinum, through which structures enter and exit the hilum. Components include: principal bronchi (two on the right, one on the left), one pulmonary artery on each side, two pulmonary veins (superior and inferior) on each side, bronchial arteries (one on the right, two on the left), bronchial veins, lymphatics, and the pulmonary plexus of nerves. The arrangement of these structures differs between the right and left lungs regarding their anteroposterior and superoinferior positions.

In the right lung's root, anteroposteriorly, it's superior pulmonary vein, pulmonary artery, and two bronchi. Superoinferiorly, it's eparterial bronchus, pulmonary artery, hyparterial bronchus, and inferior pulmonary vein. In the left lung's root, anteroposteriorly, it's superior pulmonary vein, pulmonary artery, and bronchus. Superoinferiorly, it's pulmonary artery, bronchus, and inferior pulmonary vein. The root is covered by visceral and parietal pleura, extending downwards as the pulmonary ligament, which provides dead space for venous expansion and allows the descent of the lung during inspiration.