Lungs (Pulmones)

The lungs or pulmones are the primary organs of respiration. The 2 lungs (left and right) are situated in the thoracic cavity, 1 on either side of the mediastinum enclosed in the pleural sac. The primary function of lungs would be to oxygenate the blood, i.e., exchange of O2 and CO2 between divine air and blood. Every lung is large conical/pyramidal shaped with its base resting on the diaphragm and its apex extending into the root of the neck. The right lung is bigger and heavier in relation to the left lung. The right lung weighs about 700 grams and left lung 650 grams. The right lung has 3 lobes and the left lung has 2 lobes. The lobes are divided by deep notable fissures on the surface of the lung and are supplied by 2 lobar bronchi.

The lungs are connected to the trachea and heart by primary bronchi and pulmonary vessels, respectively.

In newborn baby and individuals dwelling in clean environment, the lungs are rosy pink in color, but in individuals dwelling in polluted regions or those that are smokers, have the lungs are brownish or black in color, and mottled in appearance because of inhaled carbon particles.

In the grownups, the lungs are spongy in texture and crepitate on touch because of the presence of air inside their alveoli. They float in water. In fetus and stillborn children, the lungs are sturdy and don’t crepitate on contact as a result of absence of air in their own alveoli. They sink in water.

External Features

Every lung presents these features:

• Apex
• Base
• 3 edges (anterior, posterior, and inferior)
• 2 surfaces (costal and medial)

Anatomical Position And Side Decision

The side of lung can be decided by holding the lung in this manner that:.

• Its conical end (apex) is pointed upwards and its wider end (base) is pointed downwards,.
• Its convex surface (costal surface) is directed outwards and its flat medial surface presenting hilum is directed inwards,.
• Its thin margin (anterior margin) should face forwards and its rounded border (posterior border) should face backwards.

The side shouldn’t be established by number of fissures and lobes as they can be changeable.

The external features are discussed in detail in the subsequent text.

Apex

The apex is rounded/ dull superior end of the lung. It extends into the root of the neck about 3 cm above the anterior end of the 1st rib and 2.5 cm above the medial 1 – third of the clavicle. It’s covered by cervical pleura and suprapleural membrane.

Connections

Anterior

• Subclavian artery
• Internal thoracic artery
• Scalenus anterior

Posterior

Neck of 1st rib and structures in front of it, example, (a) ventral ramus of first thoracic nerve, (b) first posterior intercostal artery, (c) first posterior intercostal vein, and (d) sympathetic chain.

All the structures associated with the apex are divided from it by suprapleural membrane. Apex is grooved by subclavian artery on the medial side and on the front.

Clinical Significance

Pancoast Syndrome

It takes place because of engagement of structures associated with the posterior aspect of the apex of lung by the cancer of the lung apex.

Clinical Features

• Pain along the medial side of forearm and hand, and wasting of small muscles of the hand because of engagement of ventral ramus of T1.
• Horner’s syndrome, because of engagement of sympathetic chain.
• Erosion of first rib.

Cancer of lung apex may spread to include abutting structures, like subclavian or brachiocephalic vein, subclavian artery, phrenic nerve causing subsequent signs and symptoms.

• Venous engorgement and edema in neck, face, and arm due participation of subclavian and brachiocephalic veins.
• Reduced brachial and/or radial pulse because of compaction on subclavian artery.
• Paralysis of hemidiaphragm because of infiltration of phrenic nerve.
  

Base

The base is lower semilunar concave surface, which rests on the dome of the diaphragm, for this reason it’s also occasionally termed diaphragmatic surface.

Connections

On the right side, the lung is divided from the liver by the right dome of the diaphragm, and on the left side, the left lung is divided from the spleen and fundus of stomach by the left dome of the diaphragm.

The base of the right lung is deeper (i.e., more concave) because right dome of diaphragm increases to the more superior level because of the presence of liver underneath it.

Edges

The edges of the lungs are as follows:.

Anterior Border

It’s thin and shorter in relation to the posterior border. The anterior border of right lung is vertical. The anterior border of left lung presents a wide cardiac notch, that is inhabited by the heart and pericardium. In this region, the heart and pericardium is uncovered by the lung. For this reason this region is liable for an area of superficial cardiac dullness. Below the cardiac notch, it presents a tongue shaped projection named lingula.

Posterior Border

It’s thick and rounded. It stretches from spine of C7 vertebra to the spine of T10 vertebra.

Inferior Border

It’s semilunar in shape and divides the costal and medial surfaces.

Surfaces

The surfaces of the lungs are costal and medial.

Costal Surface

It’s large, smooth, and convex. It’s covered by the costal pleura and endothoracic fascia.

Connections

It’s related to the lateral thoracic wall. (In embalmed and tempered lung, the costal surface presents impressions of the ribs.).

The number of ribs related to this surface is as follows:.

• Upper 6 ribs in midclavicular line
• Upper 8 ribs in midaxillary line
• Upper 10 ribs in scapular line

Medial Surface

It’s split into 2 parts (a) small posterior vertebral part, and (b) large anterior mediastinal part.

Connections

The vertebral part is associated with the vertebral column, posterior intercostal vessels, and lesser and greater splanchnic nerves.

The mediastinal part presents a hilum, and it’s related to mediastinal structures like heart, great blood vessels, and nerves. Since the left and right surfaces of mediastinum is composed of distinct structures. The connections of the mediastinal surface of both lungs differ because structures creating left and right surfaces of mediastinum differ. To understand the connections of the mediastinal surfaces of the lungs, the pupils are counseled to know the structures creating the left and right surfaces of the mediastinum.

Structures Creating Right Surface Of Mediastinum:

• The right mediastinal surface primarily includes right atrium.
• Above the right atrium are present superior vena cava and right brachiocephalic vein.
• Behind these structures are present the trachea and esophagus.
• The azygos vein, a large venous channel, runs upwards along the side of vertebral column and arches over the root of the right lung to terminate into the superior vena cava.
• 3 neural structures, viz. (a) right phrenic nerve, (b) right vagus nerve, and (c) right sympathetic chain.

1. The phrenic nerve runs to diaphragm passing superficial to 3 venous structures from above downwards–(i) superior vena cava, (ii) right atrium, and (iii) inferior vena cava. This course is in front of the root of the lung.

2. The vagus nerve is located against the right side of the trachea and goes on the other side of the lung root. Here it breaks up into branches to take part in the formation of posterior pulmonary plexus and esophageal plexus.

3. The sympathetic trunk runs in the paravertebral gutter. The splanchnic nerves leave its lower half, run medially, and pierce the crura of diaphragm to make it to the abdomen.

Structures Creating Left Surface Of The Mediastinum:

• The left ventricle and aorta are the key structures creating the left outermost layer of the mediastinum.
• Aorta ascends at first, arches over the left lung root, and after that descends behind the lung root.
• 3 greet vessels (brachiocephalic trunk, left common carotid artery, and left subclavian vein) originate from the aortic arch and ascend up to reach the root of the neck.
• The esophagus as it descends via thorax shifts to the left behind the heart and gradually crosses the line of the descending aorta.
• 3 neural structures, viz. (a) left phrenic nerve, left vagus nerve, and (c) left sympathetic chain.

1. The left phrenic nerve crosses the aortic (left) side, enters in front of the lung root, and runs down superficial to left ventricle to get to the diaphragm.

2. The left vagus nerve is held far from the trachea by the aortic arch. Here it supplies recurrent laryngeal branch, which hooks under the aortic arch, ascends upward into the tracheoesophageal groove. Below the aortic arch, the vagus nerve runs on the other side of the lung root and breaks up into posterior pulmonary and esophageal branches.

3. The position of sympathetic trunk and splanchnic nerves is quite similar to those of the right side.

Connections Of The Mediastinal Surfaces Of The Left And Right Lungs