Lobes and fissures of lungs The right lung

Lobes and fissures of lungs The right lung is slightly larger than the left and is divided by the oblique and horizontal fissures into three lobes, the upper, middle, and lower lobes

n The oblique fissure runs from the inferior border upward and bachward across the medial and costal surfaces until it cuts the posterior border about 21/2 inches (6. 25 cm) below the apex. The horizontal fissure runs horizontally across the costal surface at the level of the fourth costal cartilage to meet the oblique fissure in the midaxillary line. The middle lobe is thus a small triangular lobe bounded by the horizontal and oblique fissures.

The left lung is divided by a similar oblique fissure (more vertical) into two lobes, the upper and the lower lobes. There is no horizontal fissure in the left lung.

Bronchopulmonary segments n Each main (primary) bronchus gives rise to lobar bronchi that supply the lobes of the lung. Each lobar (secondary) bronchus gives off branches called segmental (tertiary) bronchi

Each segmental bronchus passes to a structurally and functionally independent unit of a lung lobe called a bronchopulmonary segment

n A bronchopulmonary segment of lung tissue is pyramidal in shape, having its apex toward the root of the lung and its base toward the lung surface. Each bronchopulmonary segment is surrounded by connective tissue, and in addition to its own bronchus it receives an artery, a vein, lymph vessels, and autonomic nerves.

The bronchopulmonary segments are given the same names and numbers as the segmental bronchi. They are listed as follows:

Right lung Superior lobe 1 -Apical 2 -Posterior 3 -Anterior Middle lobe 4 - Lateral 5 -Medial Inferior lobe 6 -Superior (apical) 7 -Medial basal 8 -Anterior basal 9 -Lateral basal 10 -Posterior basal

left lung Superior lobe 1 -Apical 2 -Posterior 3 -Anterior 4 -Superior lingular 5 -Inferior lingular Inferior lobe 6 -Superior (apical) 7 -Medial basal (cardiac) 8 -Anterior basal 9 -Lateral basal 10 -Posterior basal

NB. On the right side the upper lobe bronchus arises high up from the main bronchus outside the hilum(eparterial bronchus). On the left side, the medial basal segment (7) is small because the pericardial excavation, supresses this part of the lung and its brochus usually, arises by a common stem with the anterior basal bronchus (8) thus sometimes giving rise to the erroneous impression that it is absent.

The root of the lung: It is formed of structures that are entering or leaving the lung. It is made up of the bronchi, pulmonary artery and veins, lymph vessels, bronchial vessels, and nerves. It is surrounded by a tubular sheath of pleura, which joins the mediastinal parietal pleura to the visceral pleura covering the lungs

n Bronchus: It occupies a posterior position in the hilum and can be identified by its thick cartilage wall. The right bronchus usually gives the superior lobar branch before entering into the right lung. The superior lobar bronchus may be called the eparterial bronchus because of its higher level than the pulmonary artery while the continuation of the right bronchus may be called the hyparterial bronchus because of its lower level than the pulmonary artery.

n The left bronchus usually divides after entering into the left lung so it appears as a single tube in the posterior part of the hilum.

n Pulmonary artery: It is a branch of the pulmonary trunk which carries non oxygenated blood from the right ventricle to the lung. In the right hilum, the right pulmonary artery occupies a position anterior to and in between the right bronchus and its superior lobar branch. In the left hilum, the pulmonary artery is more anterior and at a higher level than the left bronchus

n Pulmonary veins: They are two on each side, superior and inferior, that carry oxygenated blood from the lung to the left artium. The superior pulmonary vein is more anterior in position and at a lower level than the bronchus and pulmonary artery while the inferior pulmonary vein is the lowermost structure in the hilum of the lung.

n n Pulmonary (Hilar) lymph nodes: They are scattered between the main structures of the root. Bronchial vessels: They are small vessels posterior in position behind the bronchus and accompany the bronchial tree. On the right side, there is one bronchial artery while on the left side , there are two bronchial arteries (superior and inferior). The bronchial veins are usually two on each side.

n Anterior and posterior pulmonary plexuses: They are formed of sympathetic and parasympathetic fibers which lie in front of and behind the main structures of the root of the lung respectively

n Pleural sheath: It invests all structures in the root of the lung. It is the reflection between the parietal and visceral pleura with a downward extension in the form of fold called the pulmonary ligament.

Blood supply of lungs n The bronchial arteries supply the bronchi, the connective tissue of the lung, and the visceral pleura. The right bronchial artery is a branch from the right third posterior (first aortic) intercostal artery or from the superior left bronchial artery. It may arise from the descending thoracic aorta. The two left bronchial arteries are branches of the descending thoracic aorta.

n The bronchial veins forms two distinct systems. Deep bronchial veins start as intrapulmonary bronchiolar plexuses and ends in the main pulmonary vein or in the right atrium. Superficial bronchial veins drain extrapulmonary bronchi, visceral pleura and the hilar lymph nodes and drain on the right in the azygos vein while on the left, in the left superior intercostal or accessory hemiazygos veins.

Lymph drainage of lungs The lymph vessels originate in superficial and deep plexuses. The superficial plexus lies beneath the visceral pleura, the deep plexus is along the bronchi and pulmonary vessels toward the root of the lung. The vessels from the deep plexus drain into pulmonary nodes, which are located within the lung close to the hilum. All lymph from the, pulmonary nodes and from the superficial plexus drain into the bronchopulmonary nodes in the hilum. The lymph then drains into the bronchomediastinal lymph trunks

Nerve supply of lungs At the root of each lung is a pulmonary plexuses composed of efferent and afferent autonomic nerve fibres. The plexus is formed from branches of the sympathetic trunk and receives parasympathetic fibers from the vagus nerve. The sympathetic efferent fibres produce bronchodilatation and vasoconstriction. The parasympathetic - efferent fibers produce bronchoconstriction, vasodilatation, and increased glandular secretion.

Surface anatomy of the lungs The lung can be mapped out on the surface of the body as follows: The apex of the lung projects into the neck. It can be drawn on the anterior surface of the body by drawing a curved line, convex upward, from the sternoclavicular joint to a point 1 inch (2. 5 cm) above the junction of the medial and intermediate thirds of the clavicle

The anterior border of the right lung begins behind the sternoclavicular joint and runs downward and medially close to the midline behind the sternal angle (at the level of second costal cartilage). It then continues downward to the level of fourth then to the sixth costal cartilages close to the midline

The anterior border of the left lung has a similar course, but at the level of the fourth costal cartilage it deviates laterally to reach a point about 4 cm from the midline at the level of sixth costal cartilage forming the cardiac notch. This notch is produced by the heart displacing the lung to the left.

The lower border of the lung in midinspiration follows a curving line, which crosses the sixth rib in the midclavicular line and the eighth rib in the midaxillary line, and reaches the tenth thoracic spine 2 cm from midline posteriorly

The posterior border of the lung extends downward from the point of the apex (spinous process of the seventh cervical vertebra to the level of the tenth thoracic vertebra and lies about 11/2 inches (4 cm) from the midline

The oblique fissure of the lung can be indicated on the surface by a line drawn from the root(medial end) of the spine of the scapula(level of third thoracic spine) obliquely downward, laterally and anteriorly, reaching the fifth intercostal space (at the midaxillary line) and follows this to cut the inferior border at the sixth costochondral junction.

The left oblique fissure is more vertical than the right and it can be indicated by the medial border of the scapula when the arm is fully abducted above the shoulder. In the left lung the upper lobe lies above and anterior to this line; the lower lobe lies below and posterior to it. The right oblique fissure starts on the posterior border lower down than the left (level with the fourth thoracic spine).

n The horizontal fissure of the right lung may be represented by a line drawn horizontally along the right fourth costal cartilage to meet the oblique fissure in the midaxillary line and the anterior border at the level of the sternal end of the fourth costal cartilage. Above the horizontal fissure lies the upper lobe and below it, the middle lobe; below and posterior to the oblique fissure lies the lower lobe.

n N. B. The lower margins of the lungs cross the sixth, eighth, and tenth ribs at the midclavicular lines, the midaxillary lines, and the sides of the vertebral Column respectively, and the lower margins of the pleurae cross at the same points respectively, the eighth, tenth, and twelfth ribs. The distance between the two borders corresponds to the costodiaphragmatic recess.