Lungs
Lungs
Anatomy of the Lungs — Study Notes
General Characteristics
Texture
The lungs are spongy in texture.
Colour
- In the young, the lungs are brown or grey in colour.
- Gradually, they become mottled black because of the deposition of inhaled carbon particles.
Weight
The right lung weighs about 700 g; it is about 50–100 g heavier than the left lung.
External Features of Lung
Each lung is conical in shape. It has:
Apex
Upper end.
Base
Resting on the diaphragm.
Three Borders
Anterior, posterior, and inferior.
Two Surfaces
Costal and medial.
The medial surface is divided into vertebral and mediastinal parts.
Fissures
Horizontal and oblique on the right and only oblique on the left.
Lobes
On the right: Superior, middle, and inferior.
On the left: Superior and inferior.
Anatomical Position and Side Determination
For anatomical position and side determination, hold the lung in such a way so that:
- Its pointed apex is directed upward and broad base is directed downward.
- Its thin anterior border should face anteriorly, and thick rounded posterior border should face posteriorly.
- Its convex costal surface is directed laterally (toward the side of the lung — for right lung on the right side and for left lung on the left side) and mediastinal surface with hilum is directed medially.
As number of lobes and fissures are not constant, do not determine the side of the lung using lobes and fissures.
Apex
- The apex is blunt and lies above the level of the anterior end of the 1st rib.
- It reaches nearly 2.5 cm above the medial 1/3rd of the clavicle, just medial to the supraclavicular fossa.
- It is covered by the cervical pleura, the suprapleural membrane.
- It is grooved by the subclavian artery on the medial side and anteriorly.
Base
The base/diaphragmatic surface is semilunar and concave.
Relation to the Diaphragm
It rests on the diaphragm which separates:
Right Lung
The right lung from the right lobe of the liver.
Left Lung
The left lung from the left lobe of the liver, the fundus of the stomach, and the spleen.
Borders
Anterior Border
- It is very thin.
- It is shorter than the posterior border.
- On the right side: It is vertical and corresponds to the anterior or costomediastinal line of pleural reflection.
- On the left side: Shows a wide cardiac notch below the level of the 4th costal cartilage.
Posterior Border
- It is thick and ill defined.
- Corresponds to the medial margins of the heads of the ribs.
- Extends from the level of the 7th cervical spine to the 10th thoracic spine.
Inferior Border
Separates the base from the costal and medial surfaces.
Surfaces
Costal Surface
Large and convex. It is in contact with the costal pleura and the overlying thoracic wall.
Medial Surface
Divided into:
Vertebral Part (Posterior)
Related to the vertebral bodies, intervertebral discs, the posterior intercostal vessels, and the splanchnic nerves.
Mediastinal Part (Anterior)
Related to the mediastinal septum and shows a cardiac impression, the hilum and a number of other impressions which differ on the two sides.
Fissures and Lobes of the Lungs
Right Lung
Divided into three lobes (upper, middle, and lower) by two fissures (oblique and horizontal).
Left Lung
Divided into two lobes by the oblique fissure.
Oblique Fissure
- Cuts into the whole thickness of the lung, except at the hilum.
- Passes obliquely downwards and forwards, crossing the posterior border about 6 cm below the apex and the inferior border about 5 cm from the median plane.
- Due to the oblique plane of the fissure, the lower lobe is more posterior and the upper and middle lobes are more anterior.
Horizontal Fissure
- Present in the right lung.
- Passes from the anterior border up to the oblique fissure and separates a wedge-shaped middle lobe from the upper lobe.
- Runs horizontally at the level of the 4th costal cartilage and meets the oblique fissure in the midaxillary line.
Lingula
- The tongue-shaped projection of the left lung below the cardiac notch.
- Corresponds to the middle lobe of the right lung.
The lungs expand maximally in the inferior direction because movements of the thoracic wall and diaphragm are maximal towards the base of the lung. The presence of the oblique fissure of each lung allows a more uniform expansion of the whole lung.
Root of the Lung
Short, broad pedicle which connects the medial surface of the lung to the mediastinum.
Formation
Formed by structures which either enter or come out of the lung at the hilum (Latin depression).
Level
Roots of the lungs lie opposite the bodies of the 5th–7th thoracic vertebrae.
Contents
Bronchus: Principal bronchus on the left side, and eparterial and hyparterial bronchi on the right.
Pulmonary artery
Two pulmonary veins: Superior and inferior.
Bronchial arteries: One on the right side and two on the left.
Bronchial veins
Anterior and posterior pulmonary plexuses of nerves
Lymphatics of the lung
Bronchopulmonary lymph nodes
Areolar tissue
Arrangement of Structures in the Root
Right Side (From posterior to anterior side)
- Eparterial bronchus, hyparterial bronchus with bronchial vessels and posterior pulmonary plexus along their posterior walls.
- Pulmonary artery in midplane between the two bronchi.
- Superior and inferior pulmonary veins in anterior part.
- Anterior pulmonary plexus, lymph nodes, and lymph vessels in the anterior and inferior parts.
Left Side (From posterior to anterior side)
- Single bronchus with bronchial vessels and posterior pulmonary plexus along its posterior wall.
- Pulmonary artery in middle area placed above the bronchus.
- Superior and inferior pulmonary veins in anterior part.
- Anterior pulmonary plexus, lymph nodes, and lymph vessels in the anterior and inferior parts.
Relations of the Root
Anterior
Common on the two sides: Phrenic nerve, pericardiacophrenic vessels, anterior pulmonary plexus.
On the right side: Superior vena cava, a part of the right atrium.
Posterior
Common on the two sides: Vagus nerve, posterior pulmonary plexus.
On left side: Descending thoracic aorta.
Superior
On right side: Terminal part of azygos vein.
On left side: Arch of the aorta.
Inferior
Pulmonary ligament.
Blood Supply of Lungs
Arterial Supply
Bronchial Arteries
- Supply nutrition to the bronchial tree and to the pulmonary tissue.
- Small arteries that vary in number, size, and origin.
- On the right side: One bronchial artery arising from the third right posterior intercostal artery.
- On the left side: Two bronchial arteries, both arising from the descending thoracic aorta (upper opposite fifth thoracic vertebra and lower just below the left bronchus).
Pulmonary Arteries
- Deoxygenated blood is brought to the lungs by two pulmonary arteries.
- Precapillary anastomoses exist between bronchial and pulmonary arteries.
- Connections enlarge when any one of them is obstructed in disease.
Venous Drainage
Bronchial Veins
- Venous blood from first and second divisions of bronchi is carried by bronchial veins.
- Usually two bronchial veins on each side.
- Right bronchial vein: Drains into azygos vein.
- Left bronchial veins: Drain into accessory hemiazygos vein.
Pulmonary Veins
Oxygenated blood from each lung is drained by two pulmonary veins (superior and inferior) that open into the left atrium.
Lymphatic Drainage
There are two sets of lymphatics, both of which drain into the bronchopulmonary nodes:
1. Superficial Vessels
Drain the peripheral lung tissue lying beneath the pulmonary pleura. Vessels pass round the borders of the lung and margins of the fissures to reach the hilum.
2. Deep Lymphatics
Drain the bronchial tree, the pulmonary vessels, and the connective tissue septa. Run towards the hilum where they drain into the bronchopulmonary nodes.
Nerve Supply
1. Parasympathetic Nerves
- Derived from the vagus.
- Motor: To bronchial muscles, and on stimulation cause bronchospasm.
- Secretomotor: To mucous glands of the bronchial tree.
- Sensory fibres: Responsible for the stretch reflex of the lungs and cough reflex.
2. Sympathetic Nerves
- Derived from second to fifth sympathetic ganglia.
- Inhibitory to smooth muscle and glands of bronchial tree.
- Sympathomimetic drugs (like adrenaline) cause bronchodilatation and relieve symptoms of bronchial asthma.
Both parasympathetic and sympathetic nerves first form anterior and posterior pulmonary plexuses situated in front of and behind the lung roots. From the plexuses, nerves are distributed to the lungs along blood vessels and bronchi.
Clinical Anatomy
Pancoast Tumour
- Tumour of apex of the lung which typically spreads and compresses adjacent structures.
- Involvement of T1 nerve: Horner’s syndrome, pain and muscle weakness of forearm and hand.
- Involvement of recurrent laryngeal nerve: Hoarseness of voice.
- Compression of superior vena cava: Cyanosis and dilatation of veins of head and neck.
Carina
- Hook-shaped process projecting backwards from lower margin of lowest tracheal ring.
- Helps to divide trachea into two primary bronchi.
Foreign Body Aspiration
- Foreign bodies mostly descend into right bronchus as it is wider and more vertical than the left bronchus.
- Right bronchus makes an angle of 25°, while left one makes an angle of 45°.
- Enlarged lymph nodes in this area may distort the carina.
Bronchial Asthma
- Common disease of respiratory system occurring due to bronchospasm of smooth muscles in the wall of bronchioles.
- Patient has difficulty especially during expiration, accompanied by wheezing.
- Epinephrine (a sympathomimetic drug) relieves the symptoms.
Bronchogenic Carcinoma (Type of Lung Cancer)
- Most common cancer in men, mainly caused by cigarette smoking.
- Spreads to bronchopulmonary lymph nodes and supraclavicular nodes.
- Spreads (metastasize) via blood (hematogenous route) to brain, bone, suprarenal glands, and another lung.