Anatomy chapters
Lungs and pleura
The lobes, fissures, surfaces and hilum of each lung, the bronchial tree and bronchopulmonary segments, and the pleura with its surface markings and recesses.
- The right lung has 3 lobes and 2 fissures; the left has 2 lobes, 1 fissure, a cardiac notch and a lingula.
- The right main bronchus is shorter, wider and more vertical, so inhaled objects usually go right.
- The parietal pleura is pain-sensitive and extends lower than the lungs, leaving the costodiaphragmatic recess where fluid collects.
On this page
Overview
The lungs are the organs of gas exchange. Each lung lies in its own pleural cavity, on either side of the mediastinum.
The pleura is a thin serous membrane. Its two layers slide over each other as the lungs expand and recoil.
External features of the lungs
Each lung has:
- An apex that rises about 2.5 cm above the medial third of the clavicle into the root of the neck.
- A base resting on the diaphragm.
- A costal surface against the ribs and a mediastinal surface with the hilum.
Right and left lungs compared
| Feature | Right lung | Left lung |
|---|---|---|
| Lobes | 3 (upper, middle, lower) | 2 (upper, lower) |
| Fissures | Oblique and horizontal | Oblique only |
| Size | Larger and heavier; shorter because the liver pushes the diaphragm up | Smaller; has the cardiac notch and lingula |
| Main bronchus | Shorter, wider, more vertical | Longer, narrower, more horizontal |
The oblique fissure runs from about the level of the T3/T4 spine behind to the 6th costal cartilage in front. The horizontal fissure (right only) runs along the 4th costal cartilage.
The lingula of the left lung matches the middle lobe of the right lung.
The hilum
The hilum is where structures enter and leave the lung. Together they form the root of the lung.
Each root contains a main bronchus, a pulmonary artery, two pulmonary veins, bronchial vessels, lymph nodes and nerves.
| Right hilum | Left hilum |
|---|---|
| Eparterial bronchus (upper lobe bronchus) lies above the pulmonary artery | The pulmonary artery is the highest structure |
| Two bronchi (eparterial and hyparterial) | One bronchus |
The pulmonary veins lie lowest and most anterior at both hila.
The pleura around the root hangs down as a fold called the pulmonary ligament.
Only the right lung has an eparterial bronchus. On the left, the artery is the highest structure.
Bronchial tree and segments
The trachea divides at the carina, at the level of the sternal angle (T4/T5), into the right and left main bronchi.
- Main bronchi divide into lobar bronchi.
- Lobar bronchi divide into segmental bronchi, each supplying one bronchopulmonary segment.
A bronchopulmonary segment is a pyramid-shaped unit of lung with its own segmental bronchus and segmental artery. Each lung has about 10 segments. Veins run between segments.
Each segment can be removed surgically on its own because it has its own bronchus and artery, and the veins mark the planes between segments.
The right main bronchus is shorter, wider and more vertical, so inhaled foreign bodies usually enter the right lung.
When a person aspirates while lying on their back, material usually enters the apical (superior) segment of the right lower lobe, which is the most posterior branch.
Blood supply
- Pulmonary arteries: bring deoxygenated blood for gas exchange.
- Bronchial arteries: bring oxygenated blood to supply the lung tissue itself. The left ones come from the aorta; the right usually from a posterior intercostal artery.
- Pulmonary veins: carry oxygenated blood to the left atrium.
Nerve supply
The pulmonary plexus at the hilum contains:
- Vagus (parasympathetic): narrows the bronchi and increases mucus.
- Sympathetic fibres: widen the bronchi.
The pleura
- Visceral pleura covers the lungs and dips into the fissures. It has no pain fibres (autonomic supply only).
- Parietal pleura lines the inside of the chest wall, diaphragm and mediastinum. It is pain-sensitive: the costal part is supplied by the intercostal nerves, the central diaphragmatic and mediastinal parts by the phrenic nerve.
Irritation of the diaphragmatic pleura can cause pain at the tip of the shoulder (phrenic nerve, C3–C5). Irritation of the costal pleura causes sharp chest wall pain that can spread to the abdomen.
Surface markings
| Line | Lower border of lung | Lower border of pleura |
|---|---|---|
| Midclavicular | 6th rib | 8th rib |
| Midaxillary | 8th rib | 10th rib |
| Beside the vertebral column | 10th rib | 12th rib |
A widely taught memory aid: "6, 8, 10 for the lung; 8, 10, 12 for the pleura."
Recesses
Where the lung does not fill the pleural cavity, the parietal layers touch:
- Costodiaphragmatic recess: between the chest wall and the diaphragm. It is the lowest part of the pleural cavity.
- Costomediastinal recess: behind the sternum, larger on the left because of the cardiac notch.
Pleural fluid collects first in the costodiaphragmatic recess when the patient is upright.
Clinical relevance
Pleural effusion
How it happens: fluid gathers in the pleural cavity, from heart failure, infection or cancer.
What you see: breathlessness, dullness to percussion at the base and blunting of the costophrenic angle on an X-ray.
Pneumothorax
How it happens: air enters the pleural cavity, from a chest wound or a burst lung bleb.
What you see: breathlessness, reduced breath sounds and hyper-resonance on that side. In a tension pneumothorax, the mediastinum is pushed to the other side.
Chest drain and pleural tap
The usual site is the "safe triangle": the 4th or 5th intercostal space in the mid-axillary line, bounded by latissimus dorsi, pectoralis major and a horizontal line at the level of the nipple.
The needle or drain is passed just above the upper border of the rib below, because the intercostal vein, artery and nerve run along the lower border of each rib.
Do not insert a needle under the lower border of a rib: the neurovascular bundle runs there.
Inhaled foreign body
How it happens: a child inhales a nut or toy.
What you see: sudden coughing and wheeze; the object usually lies in the right main bronchus or its lower lobe branches.
Questions test the differences between the right and left lungs, the arrangement at the hilum, why foreign bodies go right, surface markings of the lung and pleura, the costodiaphragmatic recess, the nerve supply of the pleura and the safe site for a chest drain.
Quick revision
- Right lung: 3 lobes, 2 fissures. Left lung: 2 lobes, 1 fissure, cardiac notch, lingula.
- Horizontal fissure: 4th costal cartilage. Oblique: T3/T4 to 6th costal cartilage.
- Right main bronchus: shorter, wider, more vertical.
- Carina: sternal angle (T4/T5).
- Lung lower border 6, 8, 10; pleura 8, 10, 12.
- Fluid collects first in the costodiaphragmatic recess.
- Chest drain: 4th/5th space, mid-axillary line, above the rib below.
Written by The House Job from standard anatomy references (Snell's Clinical Anatomy by Regions is the book named in the UHS PGET syllabus).
FAQ
How many lobes does each lung have?
The right lung has three lobes and the left lung has two.
Why do inhaled objects usually go into the right lung?
The right main bronchus is shorter, wider and more vertical than the left.
What is a bronchopulmonary segment?
A pyramid-shaped part of a lung with its own segmental bronchus and artery, which can be removed surgically on its own.
Where is a chest drain inserted?
In the 4th or 5th intercostal space in the mid-axillary line, just above the upper border of the rib below.