Anatomy of the Human Lung

The anatomy of the human lung shows a complex network of airways and alveoli which is crucial for respiratory function and gas exchange. The human lung anatomy shows paired organs that are located in the thoracic cavity of the upper body. The lungs are the primary organ of the respiratory system.

It is the organ where the exchange of gases i.e. oxygen in and carbon dioxide out takes place. Lungs are also found in other vertebrates except fishes as they have gills to perform the exchange of gases. In this article, we will study in detail about anatomy of human lungs and its diagram.

Human Lungs

Human lungs are a muscular structure that is supported by the diaphragm and the intercostal muscles that drives the process of breathing. They are present in pairs; one on the left and one on the right side of the thoracic cavity. It along with the trachea comprises the lower respiratory tract and the duct system consisting of the nasal region, pharynx, and the larynx comprises the upper respiratory tract.

Inside the lungs, there are 300 to 500 million alveolar sacs that form the surface of the exchange of gases. When we breathe air in the lungs get filled up with atmospheric air and swell up or inflate (inspiration) and when we breathe out the air gets released out into the atmosphere and the lungs swell down or deflate (expiration).

Human Lung Diagram

The labelled diagram of human lung is given below:

Structure of the Lungs

The lungs are conical-shaped with an apex, three surfaces, three borders, and a base.

• Apex: It is a blunt end at the top (superior end), located above the level of the first rib.
• Three surfaces: The coastal surface is towards the sternum and ribs, the medial surface is towards the sternum and the vertebrae, and the diaphragmatic surface is towards the diaphragm.
• Three borders: The anterior border is thin and sharp, and in the left lungs consists of the cardiac notch, the posterior border is smooth and round, and the inferior border is sharp separating the base of the lungs from the surface of the diaphragm.
• Base: It is the bottom (inferior end) of the lungs that is placed above the diaphragm.

Anatomy of Lungs

• The lungs are cone-shaped organs that are separated from each other by the heart and other structures present in the mediastinal region of the thoracic cavity.
• The right lung is slightly bigger and heavier than the left lung and it also provides space for the heart. Together both lungs weigh around 1.3 kg and the right one is slightly heavier than the left one.
• The trachea or the windpipe branches form the right and left bronchi that enter the lungs along with the blood vessels, lymphatic vessels, and nerves through the hilum region.
• Inside the lung are the branches of bronchi called the bronchioles that end into the alveoli in which the exchange of gases takes place.
• The lungs are covered by two layers of protective covering called the pleura which have fluid in between them.
• The left lung has the cardiac notch in which the heart is placed.

Now let’s discuss anatomy of human lungs in detail.

Pleura

The lungs are covered by a protective covering of the pleura that consists of:

• The parietal pleura is located on the outer side connecting to the inner surface of the thoracic cavity.
• The pleural cavity consists of the serous pleural fluid that helps in the lubrication of the two layers of the pleura.
• The visceral pleura is located on the inner side connecting to the outer surface of the lungs.

Pleural Cavity

The pleural cavity is a thin, fluid-filled space located between the two layers of pleura. Its primary function is to provide lubrication and reduce friction during breathing movements. This cavity plays a crucial role in maintaining the shape and position of the lungs within the thoracic cavity. Additionally, it creates a pressure gradient that allows the lungs to expand and contract efficiently during respiration. Any disruption or accumulation of fluid in the pleural cavity can lead to conditions such as pleural effusion or pneumothorax, affecting breathing and lung function.

Lobes and Fissures of the Lungs

Both lungs do not have an equal number of lobes. The right lung has three lobes namely superior, middle, and inferior lobes that are separated from each other by an oblique fissure and a horizontal fissure. The left lungs have only two lobes namely superior and inferior lobes separated by the oblique fissure.

Root and Hilum

The root of the lungs is the collection of the bronchi, arteries, veins, lymphatic vessels, etc. that enters or leaves the lungs through the opening called the hilum.

Bronchial Tree

The bronchial tree is a branching network of airways within the human lungs responsible for transporting air to and from the alveoli. It begins with the trachea, which divides into two primary bronchi, one entering each lung. These bronchi then divide further into smaller bronchi and bronchioles, ultimately leading to the alveoli where gas exchange occurs. The bronchial tree is lined with ciliated epithelial cells and mucus-producing glands, which help to trap and remove foreign particles and pathogens from the airways. This intricate structure ensures efficient oxygen intake and carbon dioxide removal during respiration.

Alveoli

Alveoli also called the air sac that is the region for the exchange of gases.

• Present in millions of numbers per lung.
• The alveoli are hollow cup-shaped structures.
• Forms the functional lungs parenchyma that comprises around 90% of the total lung space.
• The alveoli are made of two types of alveolar cells or pneumocytes type I (squamous epithelium) and type II (cuboidal epithelium) cells, and an alveolar macrophage.

Diagram of Alveoli

Difference Between Right and Left Lungs

Following is the table for the differences between the right and the left lungs

Characteristics	Right Lungs	Left Lungs
No. of lobes	3	2
No. of fissures	2	1
No. of bronchus	2	1
Weight	Heavy (around 700 grams)	Light (around 600 grams)
Structure	Short and wide	Long and narrow
Cardiac notches	Absent	Present

Blood Circulation of Lungs

Blood travels in and out of the lungs through pulmonary and bronchial circulation.

• Pulmonary circulation consists of a pair of pulmonary arteries that supplies deoxygenated blood and a pair of lungs i.e. four pulmonary veins that carries the oxygenated blood from the lungs.
• Bronchial circulation consists of the bronchial arteries that bring in nutritive blood to the lungs and the bronchial veins that drain the waste-containing blood from the lungs.

Diseases of Lungs

Some of the diseases that affect the lungs are mentioned below:

• Bronchitis: Inflammation of the bronchioles.
• Asthma: Inflammation of the respiratory pathway especially the windpipe.
• COPD: Chronic obstructive pulmonary disease is caused by the destruction of the alveoli due to any possible factors.
• Cystic Fibrosis: Genetic disorder that leads to damaged lungs causing difficulty breathing.

Conclusion – Anatomy of Human Lung

In conclusion, the anatomy of the human lung is vital for understanding respiratory function and gas exchange. Lungs, located in the thoracic cavity, serve as the primary organs of the respiratory system, facilitating the exchange of oxygen and carbon dioxide. This system includes alveoli for gas exchange and pleura for protection. Additionally, the bronchial tree ensures efficient air transportation, while differences between the right and left lungs contribute to their unique functions. Exploring lung anatomy provides insights into respiratory health and diseases, highlighting the importance of proper lung function for overall well-being.

FAQs on Human Lung Anatomy

What is the Anatomy of the Lungs?

The anatomy of the lungs involves a complex structure comprising airways, alveoli, and pleura which are crucial for respiratory function and gas exchange.

What are the Main Parts of the Lungs and their Functions?

The main parts of the lungs include bronchi, bronchioles, alveoli, and pleura. Bronchi and bronchioles conduct air, while alveoli facilitate gas exchange, and pleura provides protection.

What are the Structures that are Collectively called the Root of the Lungs?

The structures that are collectively called the root of the lungs are; a bronchus per lung, a pulmonary artery per lung, two pulmonary veins per lung, bronchial vessels per lung, nerves per lung, and lymphatic vessels per lung.

What are the Functions of Type I Pneumocytes and Type II Pneumocytes?

The function of type I pneumocyte is to form the surface for gaseous exchange and the function of type II pneumocyte is to secrete surfactant to decrease the alveolar tension during the exchange of gases.

List Some of the Microbial Species that are Found in the Lungs.

The lungs house a number of microbes like Streptococcus, Staphylococcus, Pseudomonas, Aspergillus, Candida, etc.