Gross anatomy of lungs There are a pair of lungs in the thoracic cavity. Each lung is covered by pleura. Protected by thoracic skeleton. Each lung has an apex, a broad base or inferior surface, sharp anterior border, and sharp inferior border. Each lung has sterno-costal surface, diaphragmatic surface and mediastinal surface. Right lung is shorter than the left due to right lobe of liver pushing the right lung superiorly. There are 3 lobes in right lung and 2 lobes on left lung. There are two fissures in right lung, oblique and horizontal fissures. Left lung has only one oblique fissure.

The pleura is a serous membrane over the lungs It has a parietal layer and a visceral layer. The space between them is the pleural cavity, containing a scanty amount of pleural fluid. The inflammation of pleura is called as pleurisy. The parietal pleura has somatic nerve supply and it is pain sensitive. Where as visceral pleura is pain insensitive. Due to injury pleural cavity may contain blood, it is hemothorax, pyothorax if it contains pus and pneumothorax if it contains air.

The right lung The right lung displaying its two main fissures the horizontal and the oblique one. They divide the right lung into three lobs "the upper lobe, the middle lobe, and the inferior lobe“.

The left lung displaying its fissure that separates it into two lobes upper and lower.

A Pancoast tumor, labelled 'P', in the right lung of a 47-year-old female smoker

Hilum is situated on the mediastinal surface allowing structures to enter and leave the lung

The bronchopulmonary segments are

A bronchopulmonary segment is an independent unit The trachea divides into the left and right principal bronchi and enter the lung substance and divide. Each principal bronchus divides into secondary bronchi, superior lobar, middle lobar and inferior lobar bronchi. Each lobar bronchus divides in to tertiary bronchi. The lung substance attached to each tertiary bronchus constitutes a BP segment. Each segment has its own pulmonary arterial branch and thus, the bronchopulmonary segment is a portion of lung supplied by its own bronchus and artery. Each segment is functionally and anatomically discrete meaning that a single segment can be surgically removed without affecting its neighbours.

Left lung Right lung A PALM Seed Makes Another Little Palm superior lobe apical posterior anterior middle lobe lateral medial inferior lobe superior medial-basal anterior-basal lateral-basal posterior-basal Left lung superior lobe apico-posterior (merger of "apical" and "posterior") anterior lingula of superior lobe inferior lingular superior lingular inferior lobe superior anteromedial basal (merger of "anterior basal" and "medial basal") posterior basal lateral basal

As the trachea divides into two principal bronchi, the right bronchus is wider and shorter and runs more vertically than the left. Because of the right bronchus is wider and shorter and runs vertically than the left bronchus, aspirated foreign bodies are more likely to enter and lodge in it or one of its branches.

References:- Essential Clinical Anatomy-4th edition-Keith Moore( pages 68-79) http://www.rvuanatomy.com/pleura-and-lungs-checklist.html http://www.rvuanatomy.com/pleura-lungs-and-posterior-thoracic- wall.html http://radiopaedia.org/articles/bronchopulmonary-segmental- anatomy-1