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About the Lung

The lungs are vital organs of the respiratory system, responsible for exchanging oxygen and carbon dioxide with the bloodstream. They are paired organs located in the thoracic cavity on either side of the heart. 

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Lung Components

Here's a breakdown of the structure of the lung:

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  • Lobes: Each lung is divided into lobes. The right lung has three lobes – upper, middle, and lower lobes – while the left lung has two lobes – upper and lower lobes. These lobes are further divided into smaller segments.

  • Bronchial Tree:​

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Overall, the structure of the lung is highly specialized for efficient gas exchange, with a branching system of airways that lead to millions of tiny alveoli where oxygen and carbon dioxide are exchanged between the air and the bloodstream.

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  • Trachea: The trachea, also known as the windpipe, bifurcates into the left and right main bronchi at the level of the fifth thoracic vertebra.

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  • Main Bronchi: These are the primary airways that enter each lung. The right main bronchus is wider, shorter, and more vertical than the left main bronchus.

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  • Lobar Bronchi: Each main bronchus further divides into lobar bronchi, which supply air to each lobe of the lung.

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  • Segmental Bronchi: These bronchi branch into smaller segmental bronchi, which supply air to specific segments of each lobe.

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  • Bronchioles: Segmental bronchi further divide into smaller bronchioles, which lack cartilage in their walls. They continue branching into terminal bronchioles.

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  • Alveoli: Terminal bronchioles lead to clusters of tiny air sacs called alveoli. Alveoli are the site of gas exchange in the lungs. Oxygen from the air diffuses through the walls of the alveoli into the bloodstream, while carbon dioxide diffuses from the bloodstream into the alveoli to be exhaled.

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  • Respiratory Membrane: This is the interface where gas exchange occurs. It consists of the walls of the alveoli, the capillary walls, and their basement membranes.

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  • Pleura: The lungs are covered by a double-layered serous membrane called the pleura. The visceral pleura adheres to the lung surface, while the parietal pleura lines the thoracic cavity. The space between the two layers is the pleural cavity, which contains a small amount of pleural fluid, allowing the lungs to move smoothly during respiration.

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  • Blood Supply: The lungs receive blood supply from the pulmonary arteries, which carry deoxygenated blood from the heart to the lungs for oxygenation, and pulmonary veins, which carry oxygenated blood back to the heart.

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Photo Credit: Yale University

Test your Knowledge

1) How many lobes does the right lung have?

    A) One

    B) Two

    C) Three

    D) Four

 

2) What is the main function of alveoli in the lungs?

    A) Pump blood to the heart

    B) Filter out dust particles

    C) Exchange oxygen and carbon dioxide with the bloodstream

    D) Produce mucus for airway protection

 

3) What structures lack cartilage in their walls?

    A) Lobar bronchi

    B) Segmental bronchi

    C) Trachea

    D) Alveoli

 

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4) What is the function of the pleural cavity?

    A) Store excess oxygen

    B) Prevent infection in the lungs

    C) Hold the lungs in place

    D) Allow smooth movement of the lungs during respiration

 

5) What type of blood vessels carry deoxygenated blood from the heart to the lungs for oxygenation?

    A) Pulmonary arteries

    B) Pulmonary veins

    C) Aorta

    D) Coronary arteries

 

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