Phrenic Nerve It arise from the neck from the anterior rami of the 3rd; 4th and 5th cervical nerves. The right phrenic nerve: It descends in the thorax along the right side of the right brachiocephalic vein and the SVC. It passes in front of the root of the right lung and runs along the right side of the pericardium, which separates the nerve from the right atrium. Then, it descends on the right side of the IVC to the diaphragm. Its terminal branches pass through the caval opening in the diaphragm to supply the central part of the peritoneum on its underaspect.

Left phrenic nerve: It descends in the thorax along the left side of the subcalvian artery. It crosses the left side of the aortic arch and here crosses the left side of the left vagus. It passes in front of the root of the left lung, then descends over the left surface of the pericardium which separates the nerve from the left ventricle. The left lung and pleura are lateral to it. On reaching the diaphragm, the terminal branches pierce the muscle ( left copula ) and supply the central part of the peritoneum on the under aspect.

Branches: The efferent fibers are the sole nerve to supply to the muscle of the diaphragm. The afferent fibers carry sensation To the central nervous system from: 1-The peritoneum covering the central region of the undersurface of the diaphragm. 2- Diaphragmatic parietal pleura, covering the central region of the upper surface of the diaphragm and mediastinal parietal pleura. 3- Fibrous and to the parietal layer of the serous pericardium.

Vagus Nerve Right Vagus: It enters the thorax in front of the subclavian artery. It lies posterolateral to the brachiocephalic artery, then lateral to the trachea and medial to the terminal part of the azygos vein. It passes behind the root of the right lung and assists in the formation of the pulmonary plexus. On leaving the plexus, it passes onto the posterior surface of the esophagus and takes part in the formation of the esophageal plexus. It then passes through the esophageal opening of the diaphragm behind the esophagus to reach the posterior surface of the stomach.

Left Vagus: It descends in the thorax between the left common carotid and the left subcalvian arteries. Then crosses the left side of the aortic arch. It is crossed by the left phrenic nerve. It then turns backward behind the root of the left lung and assists in the formation of the pulmonary plexus. On leaving the plexus, it passes onto the anterior surface of the esophagus and shares in the formation of the esophageal plexus. It passes through the esophageal opening in the diaphragm in front of the esophagus to reach the anterior surface of the stomach.

Branches: both vagi supply the lungs and esophagus. A. The right vagus: it gives off 1- Cardiac branches. 2- The right recurrent laryngeal nerve which arises from it in the neck and hooks around the subclavian artery and ascends between the trachea and esophagus. B. The left vagus: it gives the left recurrent laryngeal nerve which arises from it as it crosses the arch of aorta. It hooks around the ligamentum arteriosum & arch of aorta and ascends in the groove between the trachea and the esophagus on the left side. It supplies the muscles acting on the left vocal cord ( except the cricothyroid which is supplied by the external laryngeal branch of the vagus in the neck ).

Pleurae They with lungs lie on either side of the mediastinum within the chest cavity. Each pleura has 2 parts: The visceral layer which completely covers the outer surfaces of the lungs and extends into the depths of the interlobar fissures ( pulmonary pleura ). The 2 layers are separated from one another by a slitlike space ( pleural cavity or space) which is filled with pleural fluid

The parietal layer which lines the thoracic wall; covers the thoracic surface of the diaphragm and the lateral aspect of the mediastinum and extends into the root of the neck to line the undersurface of the suprapleural membrane at the thoracic inlet ( outlet, clinically). The parietal pleura is divided into: 1- Mediastinal pleura It covers and forms the lateral boundary of the mediastinum. At the hilum of the lung, it is reflected as a cuff around the vessels and bronchi and here becomes continuous with the visceral pleura. It is thus seen that each lung lies free except at its hilum, where it is attached to the blood vessels and bronchi that constitute the lung root. During full inspiration the lungs expands and fill the pleural cavities.

However, during quiet inspiration the lungs do not fully occupy the pleural cavities at 4 sites : 1 & 2 are the right & left costodiaphragmatic recesses which are slitlike spaces between the costal & diaphragmatic parietal pleurae that are separated only by a capillary layer of pleural fluid. During inspiration, the lower margins of the lungs descend into the recesses. During expiration, the lower margins of the lungs ascends so that the costal & diaphragmatic pleurae come together again. 3 & 4 are the right & left costomediastinal recesses which are situated along the anterior margins of the pleura. They are slitlike spaces between the costal & the mediastinal parietal pleurae, which are separated by a capillary layer of the pleural fluid. During inspiration & expiration, the anterior borders of the lungs slide in&out of recesses.

2- Cervical pleura: It extends up into the neck, lining the undersurface of the dome suprapleural membrane ( It is a part of the deep fascia of the neck which is attached posteriorly to the transverse process of the C7 vertebra and anteriorly to the inner aspect of the 1st rib ). It reaches a level 1-1.5 inch ( 2.5- 4 cm) above the medial third of the clavicle. 3- Costal pleura: lines the inner surface of the ribs, the costal cartilage; the intercostal spaces; the sides of the vertebral bodies and the back of the sterum. 3- Diaphragmatic pleura: Covers the thoracic surface of the diaphragm. In quite respiration, it & costal pleura are in apposition to each other below the lower border of the lung. In deep inspiration, the margins of the base of the lung descends and the costal & diaphragmatic pleurae separate.

The original coelomic cavity is reduced to pleural cavity. The 2 layers become continuous with one another by means of a Cuff of pleura that surrounds structures entering and leaving the hila of the lungs. To allow for movement of the pulmonary vessels and large bronchi during respiration, the pleural cuff on the lower surface of the root hangs down as a loose fold called the pulmonary ligament.

Nerve supply of the Pleura The patietal pleura: It is sensitive to pain, temperature, touch and pressure. The costal pleura is supplied by the intercostal nerve segmentally. The mediastinal pleura is supplied by the phrenic nerve. The diaphragmatic pleura is supplied is supplied over the domes ( central ) by the phrenic nerve and around the periphery by the lower 6 intercostal nerves. The visceral pleura covering the lungs is sensitive to stretch and receives an autonomic supply from the pulmonary plexus.

The costodiaphragmatic recess is 2in. ( 5cm) deep in the scapular line posteriorly and 3- 3.5 in. ( 8- 9 cm ) in the midaxillary line and 1- 1.5 in. ( 2.5 – 4 cm ) in the midclavicular line.

Lungs The lungs are situated so that one lies on each side of the mediastinum. So, they are separated by the heart and great vessels and other structures in the mediastinum. Each lung is conical covered with visceral pleura and suspended free in its own pleural cavity, being attached to the mediastinum only by its root.

Each lung has a blunt apex which projects upward into the neck for about 1 in. ( 2.5 cm) above the clavicle. It has a concave base that sits on the diaphragm and a convex costal surface which corresponds to the concave chest wall. Its mediastinal surface is concave and is molded to the pericardium and other mediastinal structures. At about the middle of this surface is the hilum, a depression in which the bronchi; vessels and nerves that form the root enter and leave the lung. Its anterior border is thin and overlaps the heart . On the left lung the cardiac notch is found. The posterior border is thick and lies beside the vertebral column.

Lobes and Fissures Right Lung: It is larger than the left and is divided by the oblique and horizontal fissures into 3 lobes, the upper ;middle and lower lobes. The oblique fissure runs from the inferior border upward and backward across the medial and costal surfaces until it cuts the posterior border about 2.5 in. ( 6.25 cm) below the apex. The horizontal fissure runs horizontally across the costal surface at the level of the 4th 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.

Root of the lung Left lung It is divided by a similar oblique fissure into 2 lobes. The upper and lower . There are no horizontal fissure in the left lung. 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 & 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.

Innervation of the lungs The sympathetic postganglionic fibers arise from the 2nd to 5th thoracic ganglia of the sympathetic trunk. The fibers pass through the pulmonary plexuses and enter the lung where they form networks around the bronchi and blood vessels. The efferent sympathetic fibers produce bronchodilatation ( inhibitor to the bronchial tree ) and vasoconstriction ( motor to pulmonary vessels ) and inhibitor to the glands of the bronchial tree. Afferent sympathetic fibers ( impulses ) are also present ( derived ) in the bronchial mucous membrane and from stretch receptors in the alveolar walls pass to the central nervous system but their function is unknown.

The parasympathetic preganglionic fibers arise from the dorsal nucleus of the vagus and descend to the thorax within the vagus nerve. The fibers terminate by synapsing with postganglionic neurons in the pulmonary plexuses and along the branches of the bronchial tree. The postganglionic fibers enter the lung where they form networks around the bronchi and blood vessels. The parasympathetic fibers ( efferent fibers of the vagus ) are motor to the smooth muscles of the bronchial tree (bronchconstriction ) & inhibitor to pulmonary vessels ( vasodilatation ) and increase glandular secretion ( secretomotor ). Afferent fibers of the vagus nerve are sensory to the respiratory epithelium ( touch & pain ) and to the branches of the bronchial tree ( stretch receptors in the alveolar walls ).

Blood supply of the Lungs The bronchi; the connective tissue of the lung and the visceral pleura receive their blood supply from the bronchial arteries which are branches of the descending aorta. The bronchial veins which communicate with the pulmonary veins drain into the azygos and hemiazygos veins. The alveoli receive deoxygenated blood from the terminal branches of the pulmonary arteries. The oxygenated blood leaving the alveolar capillaries drains into the tributaries of the pulmonary veins which follow the intersegmental connective tissue septa to the lung root. 2 pulmonary veins leave each lung root to empty into the left atrium of the heart.

Lymph drainage of the Lungs The lymph vessels originate in superficial and deep plexuses. They are not present in the alveolar walls. The superficial ( subpleural ) plexus lies beneath the visceral pleura and drains over the surface of the lung toward the hilum, where the lymph vessels enter the bronchopulmonary nodes. The deep plexus travels along the bronchi and pulmonary vessels toward the hilum of the lung, passing through pulmonary nodes located within the lung substance; the lymph then enters the bronchopulmonary nodes in the hilum of the lung. All the lymph from the lung leaves the hilum and drains into the tracheobronchial nodes and into the bronchomediastinal lymph trunks.

Surface anatomy of theLungs 1- Apex of the lung: it lies 2.5 cm above the medial third of the clavicle. 2- Anterior border: It begins at the apex of the lung and descends downward and medially behind the sternoclavicular joint to reach a point on the median plane behind the sternal angle where the right and left borders meet. The anterior border of the right lung continues vertically downward in the median plane till it reaches the xiphisternal junction. The anterior border of the left lung passes vertically downwards in the median plane till it reaches the 4th costal cartilage then it turns to the left side to descend behind the 5th and 6th costal cartilages 0.5 inch lateral to the left border of the sternum and ends at the xiphisternal junction. This leaves part of the pericardium uncovered by lung tissue but covered by pleura only and it is called the bare area of the pericardium.

3- Inferior border of the Lung: It is similar on the 2 sides It is represented by a line convex downward It begins at the xiphisternal junction and passes downward and backward to cross the 6th rib in the midclavicular line and the 8th rib in the midaxillary line. It ends at the level of 10th thoracic vertebra 2.5 cm lateral to the median plane. 4- Posterior border of the Lung: It similar on the 2 sides It begins 2.5 cm lateral to the 10th thoracic spine and passes upward along the vertebral column to meet the apex of the lung 2.5 cm above the medial third of the clavicle ( at the level of C7 spine 2.5 cm lateral to the median plane ).

5- Oblique fissure of the lung: it is similar on the 2sides It begins at the posterior wall of the thorax opposite the 3rd thoracic spine, 2.5 cm. from the median plane. Then it passes downward and forward around the chest wall until it meets the inferior border of the lung at the 6th chostochondral junction ( 7.5 cm. from the median plane ). 6- Root (hilum ) of the Lung: Draw a vertical line parallel to the medial border of the scapula, opposite the 5th ; 6th and 7th thoracic V. 7- transverse fissure of the right Lung: It begins on the anterior wall of the thorax opposite the 4th right costal cartilage. Then, it passes transversely backward along the 4th right rib until it meets the oblique fissure near the midaxillary line.

Surface anatomy of the Pleurae 1- Apex of the pleura It is similar to the apex of the lung. 2- Anterior border of the pleura - of the right is similar to the right lung - of the left is similar to the left lung except that when it reaches the 4th costal cartilage it turns to the left side and then descends along the left border of the sternum until it reaches the xiphisternal junction. 3- Inferior border of the pleura it is similar on the 2 sides and is represented by a line convex downward. It begins at the xiphisternal junction and passes downward and backward to cross the 8th rib in the midclavicular line and the10thrib in the midaxillary line. It ends at the level of the 12th thoracic spine 2.5 cm. lateral to the median plane. 4- Posterior border of the pleura It is similar on the 2 sides. It begins at the level of the 12th thoracic spine and then is similar to that of the lung.