The Respiratory System

The Respiratory System

• Responsible for exchanging oxygen and carbon dioxide between the body and the environment
• Each alveolus is thin-walled and lies in contact with blood capillaries
• Millions of alveoli are present in each lung
• The respiratory membrane is the barrier across which gases are exchanged between air in alveoli and blood in pulmonary capillaries
• The respiratory membrane consists of the alveolar epithelium, capillary endothelium, and their joined basement membrane

Lungs

• Soft, spongy, cone-shaped organs located in the thoracic cavity
• Separated from each other by the heart and other structures in the mediastinum
• Each lung consists of four parts: apex, base, costal surface, and mediastinal (medial) surface

The Apex

• Rounded narrow superior portion that extends just slightly above the level of the middle third of the clavicle

The Base

• Broad inferior portion, concave and semilunar in shape, and fits over the convex thoracic surface of the diaphragm

The Costal Surface

• Convex surface that lies against the chest and matches the rounded curvature of the ribs

The Mediastinal (Medial) Surface

• Concave surface that contains a triangular-shaped area, the hilus, through which the bronchi, pulmonary blood vessels, lymph vessels, and nerves enter and leave
• The hilus is held together by the pleura and connective tissue and constitutes the root of the lung

The Pleural Membrane

• Two layers of serous membrane that enclose and protect each lung
• Outer layer: parietal pleura, lines the wall of the thoracic cavity
• Inner layer: visceral pleura, invests (covers) the lungs
• The space between the visceral and parietal pleura is the pleural cavity, which contains a small amount of serous fluid
• The serous fluid lubricates adjacent pleural surfaces, reducing friction during breathing, and helps the pleural membrane adhere to each other due to surface tension