Humans have a right and a left lung positioned in the chest cavity. Jointly, the lungs inhabit most of the intrathoracic space. Lungs are responsible for adding oxygen and removing carbon dioxide from the blood, thus serving as a gas-exchanging structure for respiration. Each of the lungs in humans is encased in pleura – a thin membranous sac, and each is linked with the trachea by its main bronchus, with that of the heart by pulmonary arteries.
Respiratory system in Humans
The different parts of the respiratory system in humans are –
- Nasal cavity (nose)
- Pharynx
- Larynx
- Trachea
- Bronchi
- Lungs
- Alveoli
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The anatomy of the human respiratory system begins where the air enters the body first – the nose. In addition to olfaction, the nose warms, filters and moistens in the inhaled air.
Respiratory pathway
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Nose/mouth → Pharynx → Larynx → Trachea → Bronchi → Bronchioles → Alveoli |
- Air from the nose passes to the throat or the pharynx, the cone-shaped passageway from the mouth and nose to the larynx or voice box
- Larynx is a hollow tube linked with the apex of the windpipe
- This air canal enables in speaking and prevents food from entering the lowering the respiratory tract
- From the larynx, air travels through the windpipe or trachea
- The air in the trachea is moistened and cleansed before it enters the lungs
- Clean air passes deep into the tissues of the lungs, where exchange of gasses occur
Respiration or the act of breathing, is an automatic process, regulated by the brain.
In this article, we shall discuss lungs in detail.
Simple Lungs diagram
The lung, the human gas-exchanging structure, resides in the chest (thorax) wherein its intricate tissues are protected by the muscular and bony thoracic cage.
Structure of the Lungs
The lungs are seen in the intrathoracic space, which is filled by the mediastinum. It corresponds to the connective tissue space which has the heart, vital blood vessels, the trachea with the bronchi, the esophagus and the thymus gland.
The right lung comprises three lobes – inferior, middle and superior lobe that are distinguished by an oblique and deep horizontal fissure. The left lung has two lobes separated by an oblique fissure. The apexes of the lungs expand above the first rib, while both lungs in the thorax rest with their bases on the diaphragm.
They are medially linked with the mediastinum at the hilum. The hilum is a circumscribed region wherein airways, blood and lymphatic vessels and the nerves leave or enter the lungs.
Trachea
The windpipe or trachea is present below the larynx and is lined with mucous membranes. It constitutes the main airway for the body and comprises hard cartilage which stiffens and prevents the pipe from collapsing in on itself. The oesophagus is behind the trachea.
The mucus in the trachea traps any foreign substances. This phlegm or mucus is moved to the throat where it is swallowed or expelled out by coughing.
Pulmonary segments
The lung lobes are further divided into smaller units called the pulmonary segments. There are 10 of these segments in the right lung and 8 to 10 segments in the left lung based on the classification.
Bronchi and Bronchioles
The trachea at its lower end splits in an inverted Y into the two main (stem) bronchi, one each for the right and left lung. The cartilage rings of the stem bronchi in the intrapulmonary bronchi are substituted by irregular cartilage plates. Bronchi are ensheathed by a layer of connective tissue which is continuous with the other components of the connective tissue of the lungs.
Each bronchus is divided into smaller branches that further divide into smaller branches that in turn split into tunnels called the bronchioles. The bronchioles repeatedly branch before it concludes as small air pockets which contain the alveoli.
Bronchioles are conducting airways (diameter ranges from 3 to less than a millimetre). Its walls are devoid of cartilage and seromucous glands, while its lumen has a lining of simple cuboidal epithelium with ciliated and clara cells.
Alveoli
Each bronchiole ends in spongy, tiny sacs – alveoli; each of the individual sacs is referred to as alveolus. Each alveolus fills with air when a person inhales. Together, the bronchi, bronchioles and alveoli constitute the bronchial tree.
The alveoli are surrounded by tiny blood vessels referred to as capillaries. Oxygen in the inhaled air moves through the fine alveolar walls into the capillaries. The blood vessels then distribute the oxygen to the body.
Diaphragm
At the base of the pleural cavity is the diaphragm, a sheet of strong muscles. They separate the chest cavity from that of the abdominal cavity.
The diaphragm contracts during inhalation and pulls down. At the time of exhalation, the diaphragm and the intercostals relax. The diaphragm moves upward and the ribs move in and down, forcing air out of the lungs. One full cycle of inhalation and exhalation is one breath.
This was a brief on lungs and different structures that aid the process of respiration. Visit BYJU’S for more information on the human respiratory system.
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Frequently Asked Questions on Human Lungs
Why is the right lung slightly larger than the left lung?
The right lung is somewhat larger compared to the left lung as a result of the asymmetrical position of the heart. While the right lung has 10 airway segments, the left lung comprises 8 to 10.
How many alveoli are present in lungs?
The newborn lung has only about 20 million to 50 million alveoli, while the average adult lung has approximately 300 million alveoli. Hence, an average adult has more than 600 million alveoli.
