The middle lobe is the smallest lobe of the right lung, wedge-shaped and lying between the horizontal and oblique fissures at the front. It has only two segments, lateral and medial. Its medial surface lies against the right atrium.
| Location | Anterior and lower part of the right lung, roughly between the 4th and 6th ribs in front. |
|---|---|
| Parts |
|
| Nerve Supply | Pulmonary plexus; Vagus nerve (parasympathetic, bronchoconstriction and mucus secretion); Sympathetic fibres from T2-T5 ganglia (bronchodilation) |
| Blood Supply | Right pulmonary artery (middle lobe branches); Bronchial arteries |
| Venous drainage |
|
| Lymphatic drainage |
|
Contributes a small share of gas exchange in the right lung.
The middle lobe bronchus is long and narrow and surrounded by lymph nodes, so it is prone to recurrent collapse and infection (middle lobe syndrome). Pneumonia here blurs the right border of the heart on a frontal chest X-ray (the silhouette sign). Sounds from this lobe are best heard over the front of the right chest.
Recurrent or chronic collapse of the middle lobe, from compression by lymph nodes or poor drainage of its narrow bronchus. It causes repeated infections.
Infection of the middle lobe that obscures the right heart border on X-ray. It is treated like other community pneumonia.
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