The two lungs fill most of the chest on either side of the heart. Each is wrapped in a thin double membrane, the pleura, that lets it glide smoothly as you breathe.
Lobes
The right lung has three lobes: upper, middle and lower. The left lung has only two, upper and lower, because the heart takes up space on that side; the lingula of the left upper lobe matches the right middle lobe.
Pleura
The visceral pleura covers the lung, and the parietal pleura lines the chest wall. A thin film of fluid between them lets the layers slide and holds the lung against the chest wall.
Negative pressure
The pressure in the pleural space is slightly below atmospheric pressure. This suction keeps the lung expanded, and if air or fluid gets in, the lung collapses away from the chest wall.
Pneumothorax and effusion
Air in the pleural space is a pneumothorax, fluid is a pleural effusion and blood is a hemothorax. In a tension pneumothorax, air builds up with each breath and pushes on the heart and great vessels.
| Lobe | Best heard at | Note |
|---|---|---|
| Right upper lobe | Front of the chest, above the 4th rib | Also the top of the back |
| Right middle lobe | Front and side of the right chest, below the 4th rib | Easy to miss from the back |
| Left upper lobe and lingula | Front of the left chest | The lingula matches the right middle lobe |
| Lower lobes | Back of the chest, below the shoulder blades | Mostly heard from the back |
At the bedside
Listen over every lobe, front, sides and back, because a right middle lobe problem can be missed if you only listen from behind. Absent breath sounds on one side with low blood pressure and distended neck veins suggest a tension pneumothorax that needs immediate decompression.
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Written by Making Synapses. Topic reference: OpenStax, Anatomy and Physiology 2e (no text adapted).