Pleurae Anatomy and Function

Pleurae

• The pleurae are serous membranes that line the lungs and thoracic cavity, allowing for efficient and effortless respiration.
• There are two pleurae in the body, one associated with each lung.
• Each pleura consists of a serous membrane, a layer of simple squamous cells supported by connective tissue, also known as the mesothelium.
• The pleura can be divided into two parts: visceral pleura (covers the lungs) and parietal pleura (covers the internal surface of the thoracic cavity).
• The two parts are continuous with each other at the hilum of each lung.

Costodiaphragmatic Recess

• The margins of the base of the lung decline, and the costal and diaphragmatic pleurae split up in deep inspiration.
• The lower zone of the pleural cavity into which the lung enlarges is called the costodiaphragmatic recess.

Mediastinal Pleura

• The mediastinal pleura lines the corresponding outermost layer of the mediastinum and creates its lateral boundary.
• It is represented as a cuff over the root of the lung and becomes continuous with the visceral pleura.

Cervical Pleura

• The cervical pleura is the dome of parietal pleura, which extends into the root of the neck about 1 inch (2.5 cm) above the medial end of the clavicle and 2 inches (5 cm) above the 1st costal cartilage.
• It is termed the cupola and covers the apex of the lung.
• It is covered by the suprapleural membrane.

Relations of the Cervical Pleura

• Anteriorly: subclavian artery and scalenus anterior muscle
• Posteriorly: neck of 1st rib and structures passing in front of it
• Laterally: scalenus medius muscle
• Medially: great vessels of the neck

Clinical Application: Pneumothorax

• A pneumothorax occurs when air or gas is present within the pleural space, removing the surface tension of the serous fluid and reducing lung extension.
• Clinical features: chest pain, shortness of breath, and asymmetrical chest expansion.
• Upon percussion, the affected side may be hyper-resonant due to excess air within the chest.
• Treatment: decompression to remove extra air/gas via the insertion of a chest drain.

Mediastinum

• The mediastinum is the median septum of the thorax between the two lungs.
• The ascending aorta begins at the aortic orifice and is approximately 2.5 cm in diameter.
• The arch of the aorta (aortic arch) is the curved continuation of the ascending aorta, beginning posterior to the 2nd right sternocostal joint at the level of the sternal angle.

Great Vessels

• The arch of the aorta ascends anterior to the right pulmonary artery and the bifurcation of the trachea, reaching its apex at the left side of the trachea and esophagus.
• The arch of the aorta ends by becoming the thoracic aorta posterior to the 2nd left sternocostal joint.
• The usual branches of the arch of the aorta are the brachiocephalic trunk, left common carotid artery, and left subclavian artery.

Pulmonary Fissures

• The left lung is separated into upper lobe and lower lobe by the oblique or major fissure.
• An additional transverse or minor fissure produces the middle lobe of the right lung.
• The right oblique fissure starts opposite the fourth thoracic spinous process and follows the line of the fifth rib, or a line just below, to end near the right sixth costochondral junction or just above in the fifth intercostal space.

Learn about the structure and function of the pleurae, serous membranes that facilitate respiration. Understand the visceral and parietal pleura and their roles in the thoracic cavity.