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Portrait of Lung

Anatomy · Organs & viscera

Lung

Right lung three lobes, left lung two

Thorax · respiratory system

The lungs are the paired, cone-shaped organs of gas exchange that fill most of the chest, one on each side of the heart and mediastinum. Each sits in its own pleural cavity, with its apex rising just above the first rib and its base resting on the diaphragm. The right lung has three lobes and the left has two, because the left makes room for the heart.

How to spot them

  • ▸A pair of spongy, cone-shaped organs either side of the heart, apex above the collarbone and base on the diaphragm
  • ▸The right has three lobes (upper, middle, lower) split by horizontal and oblique fissures; the left has two, split by a single oblique fissure
  • ▸The left has a notch on its front edge, the cardiac notch, and a tongue of tissue called the lingula
  • ▸Each is entered at its hilum by a bronchus, a pulmonary artery and two pulmonary veins

What to know

The paired organs whose right member has three lobes and whose left has only two

Lung — the left is smaller because the heart bulges into its side.

A tongue-shaped projection of the upper part of one of them, sitting below the cardiac notch

The lingula of the left lung, the equivalent of the right middle lobe.

Each is wrapped in a double-layered serous membrane, and air entering the space between the layers makes it collapse

Lung — the pleura; air in the pleural cavity is a pneumothorax.

Together they have a surface area often quoted at 50 to 75 square metres, thanks to some 300 to 500 million tiny air sacs

Lungs — the huge alveolar surface for gas exchange.

Their tips, or apices, poke up into the root of the neck above the first rib

Lung — a stab wound at the base of the neck can puncture the apex.

A pair of organs whose medial surface has a hilum where the main airway and the pulmonary vessels enter

Lung — the hilum is the root of the lung.

Paired organs that lie in the thorax with the diaphragm beneath and the mediastinum between them

The lungs.

Key ideas

  • Air flows down the trachea, into the main bronchi and through about 23 generations of branching to the alveoli, where oxygen and carbon dioxide swap across a barrier only a fraction of a micrometre thick.
  • The lungs have no muscle of their own. Breathing in happens when the diaphragm and intercostal muscles enlarge the chest cavity and lower the pressure inside.

Quick-fire facts

  • •The right lung is larger and heavier than the left, and has three lobes; the left has two and carries the cardiac notch.
  • •The right has two fissures (oblique and horizontal); the left has one (oblique).
  • •Each lung is divided into bronchopulmonary segments: ten on the right and eight to ten on the left, depending on how they are counted.
  • •The pleura has two layers, visceral on the lung surface and parietal lining the chest wall, with a thin film of fluid between them.
  • •The pulmonary arteries are unusual in carrying deoxygenated blood, and the pulmonary veins in carrying oxygenated blood.
  • •Aerated lung tissue floats in water, and the old hydrostatic test used this to argue that a newborn had breathed before dying.
  • •The lung root (hilum) has the pulmonary artery above, the bronchus behind and the pulmonary veins in front and below, with slight differences between sides.
  • •The lungs sit on the diaphragm; their lower borders reach the 6th rib at the midclavicular line and the 8th rib at the midaxillary line in quiet breathing.

Drill it — 8 cards

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