The structure of human lungs

The lungs occupying major portion of thoracic cavity, leave little space for the heart, which excavates more of the left lung the two lungs hold the heart tight between them, providing it, the protection it rightly deserves. There are 10 bronchopulmonary segments in each lung. Lungs are a pair of respiratory organ situated in the thoracic cavity. each lung invaginate the corresponding plural cavity. The right and left lungs are separated by mediastinum.

The lungs are spongy in texture. In the young, the lungs are brown or grey colour. Gradually, they become mottled black because of the deposition of inhaled carbon particles. The right lung weighs about 700 g, it is about 50 to 100 g heavier than the left lung. It lung is conical in shape. it has an apex at the upper end. A base resting on a diaphragm. Three borders, i. e. anterior posterior and inferior. two surfaces, i. e. costal and medial.

The medial surface is divided into vertebral and mediastinal parts. The apex is blunt and lies above the level of the anterior end of first rib. It reaches nearly 2. 5 cm above the medial one third of the clavicle, just medial to supraclavicular fossa. It is covered by cervical pleura, the suprapleural membrane, and is grooved by the subclavian artery on the medial side and anteriorly. The base is semilunar and concave. It rests on the diaphragm which separates the right lung from the right lobe of the liver, the fundus of the stomach, and this spleen. The anterior border is very thin. It is shorter than the posterior border.

On the right side, it is vertical and corresponds to the anterior or costomediastinal line of pleural reflection. the anterior border of the left lung shows a wide cardiac notch the level of 4th costal cartilage. the heart and pericardium are not covered by lung in the region of this notch. The posterior border is thick and ill defined. it corresponds to the medial margins of the head of the ribs. It extends from the level of 7th cervical spine to the 10th thoracic spine. The inferior border separates the base from the coastal and medial surfaces. The costal surface is large and convex. it is in contact with the costal pleura and overlying thoracic wall.

The medial surface is divided into posterior or vertebral part, and an anterior or mediastinal part. the vertebral part is related to the vertebral bodies, intervertebral discs, the posterior intercostal vessels and the splanchnic nerves. the mediastinal part is related to the mediastinal septum, and shows a cardiac impression, the hilum and a number of other Impressions which differ on the two sides.