Lungs

The lungs (Latin: pulmones) are an essential organ of the respiratory system located in the thoracic cavity. They are the central organ of the respiratory system. At the same time, the lungs are the final organ of the lower respiratory tract providing the inner and outer respiration and gas exchange between the human blood and inhaled air.

Anatomy of lungs

The lungs are conical in shape with a rounded point directed upwards and a flat base directed downwards that rests on the convex surface of the diaphragm.

The lungs are extending anterior and laterally from the heart to the ribs and posterior to the thoracic spine.

The lung is an expandable organ with a spongy structure. Lungs in a newborn baby have a light pink appearance. Adults during life are exposed to various substances being inhaled, so the color of the lungs in a healthy adult is darker pink or greyish pink, and the appearance is mottled.

Lungs are surrounded by the serous membrane called the pleura

It is formed by two layers- the visceral and parietal. 

The visceral part is fused with the lungs, while the parietal pleura covers the inner surface of the thoracic wall. 

Between layers is a space called the pleural cavity filled with serous fluid, allowing breathing and reducing the impedance and friction.

Each lung has an apex, base, two borders, three surfaces, and hilum of lungs.

Apex of the lungs 

The apex is a rounded upper tip of the superior end of a lung

The apex is situated above the superior thoracic aperture (thoracic inlet). More precisely, it is located in the root of the neck, where it contacts the cervical pleura. 

The supra pleural membrane covers the apex of each lung.

The apex of the lungs is located posterior to the scalene muscles. Anteriorly it is located approximately 1-2 centimeters (0.4-0.8 inches) above the clavicle or 3-4 centimeters (1.2-1.6 inches) above the first rib. 

Posteriorly it projects at the level of the spinous process of the seventh cervical vertebra.

Base of the lungs

The base of each lung is broad, semilunar, and concave lying upon the thoracic (superior) surface of the domes of the diaphragm

The concavity is more profound on the right lung base because the diaphragm lies higher on the right side than on the left because of the liver. 

That is why the right lung is broader and shorter, but the left lung is longer and narrower.

Surfaces of the lungs

Each lung has three surfaces- costal, mediastinal, and diaphragmatic surfaces. 

Lungs also contain smaller inner surfaces called interlobar surfaces. These are the surfaces between the lobes located in the gaps.

Costal surface

The costal surface of the lung is curved and convex

It contacts with the costal pleura, and it lies against the internal surface of the ribs

This surface contains rib impressions forming costal grooves.

Mediastinal surface

The mediastinal surface of the lung is also known as the medial surface. It faces the mediastinum, and it is located in the sagittal plane

The mediastinal surface is divided into vertebral and anterior mediastinal parts

The vertebral part is connected with the sides of the thoracic column. The anterior mediastinal part is deeply concave because it has a cardiac impression which is more prominent on the left lung where the heart projects.

The mediastinal surface of the lungs has several contacts with organs of the mediastinum. Therefore there are several impressions on the surface.

Both lungs feature the following impressions:

  • cardiac impression - a depression that is produced by the presence of the heart and is more pronounced on the left lung;
  • subclavian groove - a groove for the subclavian artery located on the superior lobe and going from the pulmonary apex;
  • groove for the brachiocephalic vein - runs adjacent to the subclavian groove at the apex of the lung.

Additionally, the right lung presents the following impressions:

  • impression for the azygos vein - a groove for the azygos vein that passes over the root of the right lung;
  • impression for the esophagus - a groove for the esophagus. It is located next to the impression for the azygos vein. It ascends vertically to the apex of the right lung;
  • impression for the inferior vena cava - a groove for the inferior vena cava, located anteroinferior, descends vertically from the root.

Unlike the right lung, the left lung features an impression for the aortic arch that arises above the hilum and has a curved route.

Diaphragmatic surface

The diaphragmatic surface is located inferiorly

It is smooth, concave, and corresponds to the convex dome of the diaphragm

On the right side, the diaphragm separates the lungs from the liver, but it separates the lungs from the spleen and stomach on the left side.

Borders of the lungs

The lungs have three borders- inferior, anterior, and posterior.

Inferior border

The inferior border of the lung separates the diaphragmatic surface from the costal and medial surfaces

It is thin and pointed at the site where the inferior border divides the diaphragmatic surface from the costal surface. But it is more rounded medially where it separates the diaphragmatic surface from the medial surface. 

The inferior border of the lung goes from the lowest point of the anterior border to the sixth rib at the midclavicular line. Then it goes to the eighth rib at the midaxillary line. It further continues posteriorly to the spinous process of the eleventh thoracic.

Anterior border

The anterior border of the lung is thin and sharp. It corresponds to the anterior (costomediastinal) line of the pleural reflection on the right side. But on the left, it corresponds to the same line only above the fourth costal cartilage. 

On the anterior border of the left lung lies the cardiac notch, a deep notch created by the apex of the heart. 

Below the notch is situated the lingula of the left lung, a tongue-like projection of the superior lobe of the left lung.

Posterior border

The posterior border of the lung is thick, and it divides the costal surface from the mediastinal surface.

Hilum of the lung 

The hilum is a large triangular-like depressed area near the center of the mediastinal surface of each lung

It is located posterior to the cardiac impressions of both lungs between the 5th and 7th thoracic vertebrae. 

It is situated more in the posterior part of the mediastinal surface. 

The hilum is the site where various anatomical structures enter and leave the lung via the root of the lung.

The root of the lung

The root of the lung is a short and broad pedicle formed by a collection of structures that connect the lungs to the heart, trachea, and surrounding anatomical structures

The visceral pleura covers all surfaces of the lungs except the hilum. Instead, it forms a covering over the root of the lung, also known as the sleeve of the pleura

Parietal and visceral pleura are continuous at the hilum, and it is a site where both parts connect. 

The pleura extends inferiorly and forms a pulmonary ligament.

Structures in the root of the lungs

Structures included in the root are the principal and lobar bronchi, pulmonary artery, two pulmonary veins, bronchial branches from the thoracic aorta, bronchial veins, pulmonary nerve plexuses, lymphatic vessels, bronchopulmonary lymph nodes, and loose connective tissue

In the lung roots, the topography of these structures is different for both lungs. 

The sequence of structures in both lungs

From top to bottom, in the right lung, the most superior is located the right principal bronchus, then right pulmonary artery, and the lowest location has the right pulmonary veins.

In the left lung, the most superior is located the left pulmonary artery, in the middle is situated the left principal bronchus, the lowest location have the left pulmonary veins. 

Anteroinferior to the pulmonary artery and anterior to the principal bronchus is located upper pulmonary vein.

Anatomical relations

The root of the right lung is located behind the superior vena cava, part of the right atrium, and beneath the azygos vein. 

The root of the left lung is situated beneath the aortic arch and anteriorly to the descending thoracic aorta.

In front of each root are situated the phrenic nerves, anterior pulmonary plexus, and pericardiacophrenic artery and vein. 

Posterior to each root is located the vagus nerve and posterior pulmonary plexus.

The area that is situated next to the root is called the perihilar area.

Lobes and subdivisions of the lungs

Every lung by various fissures is divided into smaller parts called lobes. And every lobe splits into even smaller regions called segments

The bronchopulmonary segment is the anatomical, physiological and surgical unit of the lungs. 

Surgical removal of a segment does not affect the function of the other segments.

The segments have a conical shape. They are separated from each other by a layer of connective tissue. 

The bases of the segments face the outer surface of the lungs. But their apex faces the hilum of the lung. 

Along the center of the segment, go and give branches segmental bronchi and artery.  

Segmental veins are located in the connective tissues located between the segments. 

Segments are further divided into lobules. They are hexagonal divisions and the smallest subdivisions that are visible by the naked eye.

Every lung contains a different amount of fissures, lobes, and segments.

Right lung

The right lung is one of two lungs situated on the right side of the heart and mediastinum. 

As mentioned before, the right lung is shorter than the left due to the liver lying beneath, causing the right hemidiaphragm to be higher. 

The right lung is wider than the left lung due to the impression of the heart on the left lung. Therefore, it has a greater capacity and weight than the left lung. 

Another difference between the right and left lungs is that the right main bronchus is longer. It has a broader caliber and is more vertical than the left main bronchus.

The right lung is divided into three lobes by an oblique and horizontal fissure.

These lobes are:

  • superior,
  • middle (most minor),
  • inferior.

Fissures 

The oblique fissure, also known as the major or great fissure, divides the inferior lobe from the middle and superior lobes

The oblique fissure begins at the level of the spinous process of the third thoracic vertebra. It goes obliquely along the costal surface forward and downwards. It crosses the fifth intercostal space and then ends at the inferior border of the lung. It follows the contour of the sixth rib to the sixth costochondral junction.

The horizontal fissure, also known as the minor fissure, is a short fissure that divides the superior and middle lobes. It arises from the right oblique fissure starting from the right midaxillary line. It goes at the fourth rib level forward to the anterior border. 

It reaches the sternal end of the fourth costal cartilage; further, it passes the mediastinal surface and ends at the hilum.

Bronchopulmonary segments

The right lung has ten bronchopulmonary segments.

The superior lobe of the right lung consists of three bronchopulmonary segments:

  • apical segment,
  • posterior segment,
  • anterior segment.

The middle lobe has two bronchopulmonary segments:

  • lateral segment,
  • medial segment.

The inferior lobe of the right lung consists of five bronchopulmonary segments:

  • superior segment,
  • anterior basal segment,
  • medial segment,
  • lateral basal segment,
  • posterior basal segment.

Left lung

The left lung is situated in the left part of the mediastinum and on the left side of the heart.

The left lung is divided into two lobes by an oblique fissure:

  • superior lobe,
  • inferior lobe.

The inferior lobe is larger than the superior one.

Fissure

The left oblique fissure, also known as the major or great fissure, is more vertical than the right oblique fissure. 

The left oblique fissure arises from the mediastinal surface of the hilum, ascends obliquely backward, crossing the posterior border of the lung. Further, the left oblique fissure passes anteriorly downwards across the costal surface, and in the end, it ascends on the medial surface to the hilum.

Bronchopulmonary segments

The left lung has eight bronchopulmonary segments.

The superior lobe of the left lung consists of four bronchopulmonary segments:

  • apicoposterior segment,
  • anterior segment,
  • superior lingular segment,
  • inferior lingular segment.

The inferior lobe of the left lung has four bronchopulmonary segments:

  • superior segment,
  • anteromedial basal segment,
  • lateral basal segment,
  • posterior basal segment.

Position of the lungs

Both lungs are located in the thoracic cavity on both sides of the mediastinum. 

Both lungs have similar positions and boundary lines, although each slightly differs.

Common anterior boundary line

The anterior border of the lungs passes from the apex obliquely downwards and anterior, projecting behind the sternoclavicular joint. Further, the anterior border of the lungs runs behind the sternum. Then it goes medially. 

The level around the second and fourth rib is the closest point between the right and left lungs. 

Reaching the level of the fourth rib, the anterior border of the lungs is different on each side. 

Anterior boundary line of the right lung

On the right lung, the anterior border further descends obliquely and reaches the upper margin of the sixth rib on the right parasternal line. After that, the anterior border continues as the inferior border. 

Anterior boundary line of the left lung

On the left lung, the anterior border at the fourth rib turns horizontally and passes along the fourth rib reaching the left parasternal line. 

Then the anterior border of the left lung descends and, on the left midclavicular line, reaches the inferior margin of the sixth rib. 

Further, the anterior border of the left lung continues as the inferior border that has a similar course as on the right lung. 

Common inferior boundary line

The inferior border of the right lung crosses the following lines:

  • right midclavicular line at the level of the upper margin of the sixth rib,
  • right anterior axillary line at the level of the seventh rib.
  • right midaxillary line at the level of the eighth rib,
  • right posterior axillary line at the level of the ninth rib,
  • right scapular line at the level of the tenth rib,
  • right paravertebral line at the level of the spinous process of the eleventh thoracic vertebrae.

Common posterior boundary line

The posterior border of the right and left lungs passes upwards along the spine to reach the level of the second rib, where it continues as the apex of the lungs.

Microanatomy of lungs

The lungs bear a strong resemblance to the structure of a composed alveolar gland as each lobe of the lungs is divided by the connective tissue into segments.

Lungs contain the bronchial and alveolar parts, also known as the trees. 

The alveolar part is the respiratory part of the lungs.

Bronchial tree

The bronchial tree starts with the principal bronchus that branches into lobar bronchi and further into segmental bronchi. 

Segmental bronchi divide into intrasegmental or lobular bronchi

Finally, the intrasegmental bronchi divide into terminal bronchioliwith whom ends the bronchial tree

Bronchi with a diameter of 2-5 millimeters are the medium bronchi. The small bronchi have a diameter of 1- 2 millimeters. 

Small bronchi with a diameter of 0,5-1 centimeters are called the bronchioles.

Terminal bronchiole is approximately 0,5 millimeters wide.

Types of bronchi

There are two types of bronchi according to the structure of the wall- the cartilaginous and muscular bronchi

Large bronchi contain a significant amount of cartilages, but as they branch further and divide into smaller bronchi, the amount of cartilages decreases, but the number of smooth muscle cells increases.

Cartilaginous bronchi are large and medium, but the muscular bronchi are the small ones.

Wall of the bronchi

The wall of the cartilaginous bronchi is composed of mucosa, submucosa, and fibrous cartilaginous layer, muscular layer, and adventitia. 

But the wall of the muscular bronchi contains the mucosa, submucosa, muscular layer, and adventitia

All bronchi have well developed muscular layer. 

Bronchi are lined by pseudostratified ciliated columnar epithelium. As the bronchial caliber decreases, the rows in epithelium become lower.

The epithelium contains ciliated cells, goblet cells, cylindric and endocrine cells.

The connective tissue of the mucosa is composed of many elastic fibers and small lymphatic follicles.

The fibrous cartilaginous layer is made of fibrous tissue and individual cartilage plates. Large bronchi contain hyaline cartilages, but as the diameter of the bronchi decreases, hyaline cartilages transform into elastic cartilages. Middle bronchi have only elastic cartilages.

The fibrous cartilaginous part also contains bronchial glands

The muscular layer is formed by longitudinal and circular bundles of smooth muscle cells.

Wall of the bronchioles

The composition of the wall of the bronchioles is very similar to small bronchi. It also has only the mucosa, submucosa, muscular layer, and adventitia.

Bronchioles are lined by simple columnar ciliated epithelium. It contains goblet cells and Clara cells, also known as the club cells, with short microvilli. These cells secrete the glycosaminoglycans and enzymes. 

Bronchioles do not have glands.

Under the epithelium is a skinny connective tissue layer, and under it is located a network of smooth muscle cell bundles.

Adventitia is related to the surrounding interlobar connective tissue.

Alveolar tree

Terminal bronchiole is the origin of the morphofunctional unit of the lobules located distally to bronchioles and to which the alveoli give the appearance of a bunch of grapes. It is called the pulmonary acinus. 

It contains respiratory bronchioles dividing into alveolar ducts that end with two alveolar sacs containing alveoli. 

The walls of the alveolar sacs and ducts are composed of the alveoli. Every lung contains approximately 300-400 million alveoli.

Respiratory bronchioles are divided into three subdivisions. 

Wall of respiratory bronchioles

Respiratory bronchioles are lined with simple ciliated cuboidal epithelium proximally, but distally there are no cilia as they gradually disappear. The respiratory bronchioles under the epithelium contain connective tissue and bundles of smooth muscle cells and adventitia. 

The smooth muscle layer is thin.

Wall of alveoli

Alveoli are lined with very thin, simple squamous epithelium.

Between the alveoli is a very thin layer of connective tissue containing capillaries and nerve fibers.

Alveoli form the respiratory membrane together with capillaries. Through the membrane happens the gas exchange.

The membrane is formed by the squamous cells of an alveolus, the basement membrane of an alveolus and the capillary, and also the endothelium of the capillary.

Cells of the alveolar wall are called the pneumocytes. There are two types of pneumocytes- type I and type II. 

Mainly the wall of alveoli contains the type I pneumocytes, which provide the gas exchange.

Type II pneumocytes secrete surfactant preventing the lungs from collapse and repairing the alveolar epithelium.

Connective tissue contains many macrophages, called dust cells, phagocyting dust, viruses, microbes, and dead cells.

Lung functions

The primary function of the lungs is to provide the outer and inner respiration processes.

During external respiration, the lungs fill up with the air by inhalation, and the air is released to the atmosphere by exhalation

But during internal respiration, the lungs provide the gas exchange between the inhaled air and the blood. Oxygen and carbon dioxide are exchanged between the tissue, but it is not the only function lungs provide.

  • The lungs participate in thermoregulation.
  • They participate in the metabolism of biologically active substances
  • Lungs participate in the regulation of homeostatic functions and blood clotting as they produce thromboplastin and heparin.
  • Lungs maintenance the water balance.
  • They provide the regulation of acid-base balance and pH balance.
  • In the capillaries of the lungs, angiotensin I is converted to angiotensin II, which is involved in the regulation of blood pressure.
  • Various substances are excreted through the lungs. For example, in the case of uremia, urea is excreted.
  • The lungs play a role in the defenses against various antigens with immunoglobulin A, complement activation, lymphocytes, leucocyte recruitment, cytokines, and growth factors.
  • Lungs provide the mucociliary clearance with which the particles of dust and bacteria are moved upward out of the lungs.
  • Lungs also can work as a blood reservoir as they can store a massive amount of it. Lungs interact with the heart and provide to function it more efficiently.
  • Lungs work as a filter for tiny gas bubbles that can occur in the bloodstream.

A person can live with only one lung as it can provide all the mentioned functions.

Respiration process

The main function of the lungs is to provide inner and outer respiration by removing carbon dioxide from the blood and uptaking oxygen into the blood. 

Inspiration

Inspiration is an active process

When the diaphragm and muscles of inspiration contract, the diaphragm pulls the diaphragmatic surfaces of the lungs downward. But the muscles of inspiration raise the rib cage. It increases intrathoracic volume creating a negative pressure within the pleural space, and sucks in air through the upper respiratory tract into the trachea, airways, and then into the alveoli, where the gas exchange occurs. 

During peaceful breathing, the muscles of the inspiration are the diaphragm and external intercostal, interchondral part of internal intercostal muscles.

But during intensive breathing also participate the accessory muscles of the inspiration- sternocleidomastoid, scalene muscle group, serratus anterior, pectoralis minor and major, trapezius, lattisimus dorsi, quadratus lumborum.

Expiration

The expiration is mostly a passive process

During expiration, the diaphragm relaxes, and the elastic recoil of the lungs, chest wall, and abdominal structures compresses the lungs and expels the air.

During peaceful and quiet breathing, the expiration results from passive recoil of lungs and rib cage.

The muscles of the expiration participate during forced expiration. 

They are the rectus abdominis, the internal intercostals except for the interchondral part, transverse abdominis, external oblique, and internal oblique muscles.

Neurovascular supply

Arterial blood supply

The arterial blood supply of the lungs includes bronchial circulation and pulmonary circulation

The bronchial circulation is a part of the systemic circulation and includes the bronchial arteries, but the pulmonary circulation consists of the pulmonary arteries.

The bronchial arteries supply oxygenated blood to the lungs. But the pulmonary arteries contain deoxygenated blood pumped from the right ventricle via the pulmonary trunk. 

In the lungs happens the gas exchange as deoxygenated blood becomes oxygenated and reaches the left atrium via four pulmonary veins.

Pulmonary arteries

The pulmonary trunk arises from the infundibulum of the right ventricle. It passes posteriorly and slightly upwards and below the aortic arch divides into left and right pulmonary arteries. 

The right pulmonary artery passes posteriorly and near the hilum divides into superior, middle, and inferior branches, supplying the upper, middle, and lower pulmonary lobes. 

The left pulmonary artery passes posterosuperior, enters the hilum of the left lung, and divides into superior and inferior branches, which supply the upper and lower lobes. 

The left pulmonary artery also has a singular branch supplying the lingula.

Further, these branches divide into pulmonary capillaries that form a network around the alveoli.

Bronchial arteries

Usually left side contains two bronchial arteries, while the right lung only one.

Bronchial arteries primarily provide the blood supply for bronchi, lung roots, visceral pleura, pulmonary vessels and aorta, vagus nerve, connective, and supporting lung tissue.

The left bronchial arteries (superior and inferior) arise from the thoracic aorta

The superior left bronchial artery supplies part of the aortic arch, but the inferior left bronchial artery supplies the bronchi and connective tissue in the hilum.

The origin of the right bronchial artery is variable. It may arise from one of the following: the thoracic aorta, the superior bronchial artery on the left side, or the right intercostal arteries. 

In a word, it arises from the intercostobronchial trunk.

The bronchial arteries run with and branch along with the bronchi, ending at the level of the respiratory bronchioles. 

Venous drainage

Bronchial and pulmonary veins provide venous drainage of the lungs.

Bronchial veins

The bronchial veins are usually one on each side formed by the superficial and deep bronchial veins

The bronchial veins drain into the pulmonary veins.

Bronchial veins drain the hilum of the lungs, bronchi, and lung tissue.

Lungs contain intra- bronchial venous plexuses forming the deep bronchial veins. 

The subpleural venous plexuses are the tributaries of the superficial bronchial veins. 

Superficial bronchial veins drain into accessory hemiazygos, brachiocephalic, left superior intercostal veins (left lung), and azygos vein (right lung).

Pulmonary veins

The pulmonary veins are two on each side, and they carry oxygenated blood from the lungs to the heart

The pulmonary veins arise from the pulmonary capillary network that joins together and forms a single trunk. 

Capillaries form intrasegmental veins unite and form segmental veins. Segmental veins merge, forming intersegmental veins, which combine in lobar veins. 

The right lung has three lobar veins, and the left lung two.

Lobar veins merge, forming pulmonary veins, which drain the parenchyma of the lungs. 

The pulmonary veins emerge from each lung at the hilum and drain into the left atrium. 

On its course, the pulmonary veins also receive the bronchial veins.

Lymphatic drainage

The lymphatic drainage is provided by the subpleural or superficial plexus located below the pleura and the deep plexus

The superficial division lies under the visceral pleura. It drains the parenchyma of the lungs to the ipsilateral bronchopulmonary lymph nodes at the hilum.

The deep plexus lies along the bronchial tree and pulmonary blood vessels. It drains deeper structures

Plexus drains into pulmonary nodes within the lung parenchyma and next to bronchopulmonary nodes.

The lower lobes of the lungs are drained via the inferior tracheobronchial nodes, but the superior lobes via superior tracheobronchial nodes

Lungs also contain deep intrapulmonary lymph nodes.

From tracheobronchial nodes, lymph drains next to paratracheal lymph nodes and then to the right and left bronchomediastinal trunks

From bronchomediastinal trunks, lymph drains into the thoracic duct on the left side and to the right lymphatic duct on the right side.

Innervation

The lungs receive nerve supply through the vagus nerve (CN X) and the sympathetic trunk. 

Nerves form the pulmonary plexuses lying anterior and posterior to the structures going through the hilum.

The anterior pulmonary plexus is a continuation posteriorly from the superficial cardiac plexus. It includes cardiac branches of superior cervical ganglia from the sympathetic trunk and superior cardiac branches from the vagus nerve.

The posterior pulmonary plexus is a continuation laterally from the deep cardiac plexus. It contains cardiac branches of cervical ganglia, cardiac branches of thoracic ganglia (T1-T5) from the sympathetic trunk and cardiac branches, and recurrent laryngeal nerves from the vagus nerve and its branches.

Plexuses also include bronchial branches of the vagus nerve

Sympathetic efferent impulses are realized through the thoracic sympathetic and cervical sympathetic ganglia.

The parasympathetic system provides the stimulation of secretion from bronchial glands, bronchial smooth muscle contractions, and the vasodilatation of the pulmonary vessels.

The sympathetic system provides opposite effects. It causes the relaxation of the bronchial smooth muscles and vasoconstriction.

Visceral afferent nerve fibers from the vagus nerve provide the pain sensation, although lungs don’t have a significant amount of pain receptors. Usually, when a person has and feels pain in the lungs, it comes from other structures or the pleura. 

Summary on lungs

What is a lung?

The lungs are an essential and central organ of the respiratory system located in the thoracic cavity. At the same time, the lungs are the final organ of the lower respiratory tract providing the inner and outer respiration and gas exchange between the human blood and inhaled air.

Where are the lungs in the human body?

The lungs are located in the thoracic cavity.

Are both lungs the same?

No, they are not. The right lung is shorter than the left due to the liver lying beneath, causing the right hemidiaphragm to be higher. The right lung is wider than the left lung due to the impression of the heart on the left lung. Therefore, it has a greater capacity and weight than the left lung. Another difference between the right and left lungs is that the right main bronchus is longer. It has a broader caliber and is more vertical than the left main bronchus.

What are the parts of the lungs?

The lungs contain the apex and base. Every lung has three borders and surfaces.

What is the function of the lungs?

The primary function of the lungs is to provide the outer and inner respiration processes. During external respiration, the lungs fill up with the air by inhalation, and the air is released to the atmosphere by exhalation. But during internal respiration, the lungs provide the gas exchange between the inhaled air and the blood. 

Are lungs muscular?

Although lungs contain muscle fibers, it is not a very muscular organ.

Are lungs a muscle or organ?

Lungs are the central organ of the respiratory system.

Do the lungs hurt?

Lungs don’t have a significant amount of pain receptors. Usually, when a person has and feels pain in the lungs, it comes from other structures or the pleura. 

How do lungs look?

The lungs are conical in shape with a rounded point directed upwards and a flat base directed downwards that rests on the convex surface of the diaphragm. The lungs have a spongy structure. Lungs in a newborn baby and healthy individuals have a light pink appearance. Adults during life are exposed to various substances being inhaled, so the color of the lungs in a healthy adult is darker pink or greyish pink, and the appearance is mottled.

Can you live without lungs?

A person can live with only one lung as it can provide all the mentioned functions.

Why is lung health important?

The lungs are a central organ of the respiratory system. It is vital to have healthy lungs as they provide the gas exchange between the human body and the blood. 

In a word, they provide the human body with oxygen. Therefore, the human can live.