2. The Lung

3. Objectives Explain pleura. Define mediastinum.
Discuss the anatomical structure of lungs.
Enlist the relations of right and left lungs.
Give the blood and nerve supply of the lungs.

4. The pleura:
Has two parts:
A parietal layer, which lines the thoracic wall, covers the diaphragm, the lateral aspect of the mediastinum, & line the suprapleural membrane.
A visceral layer, which covers the outer surfaces of the lungs and extends into the interlobar fissures.
The parietal and visceral pleura are separated by the pleural cavity.

5. The parietal pleura is divided into:
Cervical pleura.
Costal pleura.
Mediastinal pleura.
Diaphragmatic pleura.
The pulmonary ligament is a pleural fold surrounding structures entering and leaving the lung.

6. Nerve Supply of the Pleura:
The parietal pleura is sensitive to pain, temperature, touch, and pressure and is supplied as follows:
The costal pleura by the intercostal nerves.
The mediastinal pleura by the phrenic nerve.
The diaphragmatic pleura over the domes by the phrenic nerve and around the periphery by the lower six intercostal nerves.
The visceral pleura covering the lungs is sensitive to stretch but is insensitive to common sensations such as pain and touch. It receives an autonomic nerve supply from the pulmonary plexus.

7. The mediastinam is the space between the two pleural cavities.
The mediastinum is divided into superior and inferior mediastina by an imaginary plane passing from the sternal angle anteriorly to the lower border of the body of the fourth thoracic vertebra posteriorly.
The superior mediastinum is bounded in front by the manubrium sterni and behind by the first four thoracic vertebrae.
Superior mediastinum contains thymus, large veins, large arteries, trachea, esophagus , thoracic duct, and sympathetic trunks.

8. The inferior mediastinum is bounded in front by the body of the sternum and behind by the lower eight thoracic vertebrae.It is divided into:
Anterior mediastinum contains the thymus.
Middle mediastinum contains the pericardium, heart & phrenic nerves .
Posterior mediastinum contains esophagus, thoracic duct, descending aorta, and sympathetic trunks.

9. The lungs are situated one on each side of the mediastinum.
Each lung has:
An apex.
A concave base.
A convex costal surface.
A concave mediastinal surface.
At about the middle of mediastinal surface is the hilum, a depression in which the bronchi, vessels, and nerves that form the root of the lung enter and leave the lung.

10. Each lung has:
An anterior thin border that overlaps the heart.
A posterior thick border that lies beside the vertebral column.
The right lung is slightly larger than the left and is divided by the oblique and horizontal fissures into three lobes:
Upper, middle, and lower lobes.

11. The medial surface of the right lung related to:
Inferior vena cava.
Superior vena cava.
Azygos vein.
Esophagus.

12. The left lung is divided by an oblique fissure into two lobes:
The upper and lower lobes. There is no horizontal fissure in the left lung.

13. The medial surface of the left lung related to:
The heart.
Aortic arch.
Thoracic aorta.
Esophagus.

14. Bronchopulmonary Segments:
The bronchopulmonary segments are the anatomic, functional, and surgical units of the lungs.
Each lobar (secondary) bronchus gives off segmental (tertiary) bronchi.
Each segmental bronchus passes to a structurally and functionally independent unit of a lung lobe called a bronchopulmonary segment, .

15. The main bronchopulmonary segments are:
Right lung:
Superior lobe: Apical, posterior & anterior segments.
Middle lobe: Lateral, medial segments.
Inferior lobe: Superior (apical), medial basal, anterior basal, lateral basal, posterior basal segments.
Left lung:
Superior lobe: Apical, posterior, anterior, superior lingular, inferior lingular segments.

16. 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.
The bronchial veins drain into the azygos and hemiazygos veins.
The alveoli receive deoxygenated blood from the terminal branches of the pulmonary arteries.

17. Lymph from the lung drains into the tracheobronchial nodes and then into the bronchomediastinal lymph trunks.
Nerve supply of the lungs is by a pulmonary plexus which is formed from branches of the sympathetic trunk and receives parasympathetic fibers from the vagus nerve.