Respiratory system: Structure and function

Definitions & Key takeaways

The respiratory system consists of the lungs and the structures that make up the airway. Air enters through either the nose or the mouth, making its way to the pharynx and then the larynx, followed by the trachea, where it branches off to the left and right bronchi, which divide off in the lungs into smaller bronchioles that end in clusters of alveoli.

The respiratory system specifically functions in respiration, which involves two processes: ventilation, which is the mechanical process of moving air into and out of the lungs, and gas exchange, which is the process by which inhaled oxygen enters the blood from the alveoli, and carbon dioxide exits the blood into the alveoli to be exhaled.

There are some important muscles involved in ventilation. The first is the diaphragm, which is the dome-shaped muscle at the base of the chest that separates the chest and abdominal cavities. There are also intercostal muscles, the muscles between our ribs, which aid in the expansion and retraction of the chest walls, supporting the diaphragm during ventilation.

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Intro0:00–0:41

The respiratory system consists of the structures in our bodies that allow us to breathe. It is made up of the lungs and a collection of tubes and passages called the “airway.” It’s often thought of as consisting of two regions: the upper respiratory tract and lower respiratory tract.
The upper respiratory tract includes the nose, nasal cavity, the oral cavity, pharynx, larynx, and the upper part of the trachea; the lower respiratory tract includes the lower part of trachea, bronchi, bronchioles, and the lungs.The tubes and passages that make up the airway serve to move air into and out of the lungs.

Main Parts of the Respiratory System: The Airway0:41–1:43

Air enters the body either through the nostrils of the nose and into the nasal cavity, which is the air-filled space behind the nose, or through the mouth, also known as the oral cavity.
Both entryways lead air to the pharynx: the cavity behind the nose and mouth, more commonly known as the throat. From there, air travels down into and through the larynx, otherwise known as the “voice box” because it contains the vocal cords necessary for producing speech.
After passing through the larynx, air begins to move into the trachea, the tube known as the “windpipe” that branches off at its base into two tubes: the left and right bronchi, which lead to the left and right lung.
Each of the bronchi branches off further and further within the lungs into many smaller and smaller tubes, called bronchioles, at the end of which are bunches of tiny air sacs, called alveoli, which are surrounded by tiny blood vessels, called capillaries.Now, healthy lungs are pink, spongy, and elastic.

Main Parts of the Respiratory System: The Lungs1:43–2:19

The right lung is divided into 3 lobes, while the left lung is divided into only 2 lobes and is a bit smaller than the right lung because of the space taken up by the heart in the left side of the chest cavity.
Each of the lungs is covered by the pleura: a 2-layered sac with a fluid-filled space between the two layers. One of the layers is attached to the lung, and the other is attached to the chest wall.The fluid between the two layers acts like a lubricant and decreases the friction between the layers as the lungs expand when we breathe.
Now, the respiratory system’s function is respiration, which actually includes two distinct processes: ventilation and gas exchange.

Respiratory System Functions: Ventilation2:19–3:27

Ventilation is the mechanical process of getting air into and out of the lungs. This involves inspiration, which is breathing air in, and expiration, which is breathing air out.
There are some important muscles involved in ventilation. The first is the diaphragm, which is the dome-shaped muscle at the base of the chest that separates the chest and abdominal cavities.
During inhalation, the diaphragm contracts and moves downward, increasing the size of the chest cavity. This creates negative pressure inside the lungs that sucks air in.
During exhalation, the diaphragm relaxes and moves upward, decreasing the size of the chest cavity and allowing air to flow out of the lungs, back up the airway, and out of our nose or mouth.
The intercostal muscles, the muscles between our ribs, aid in the expansion and retraction of the chest walls, supporting the diaphragm during ventilation.Now, the second component of respiration, gas exchange, involves getting oxygen into and carbon dioxide out of the blood!

Respiratory System Functions: Gas Exchange3:27–4:09

This happens at the level of the alveoli, which are the functional units of the lungs. Alveoli have very thin walls, and they are lined with a bunch of tiny blood vessels, called capillaries, which also have very thin walls.
The thinness of these walls allows gases, like oxygen and carbon dioxide, to easily diffuse across. During gas exchange, the oxygen in the alveoli diffuses into the oxygen poor blood, while the carbon dioxide abundant in the blood moves into the alveoli and gets breathed out.

Effects of Aging on the Respiratory System4:09–5:11

As we age, we lose tissue elasticity and muscle mass. In the respiratory system, both of these changes reduce the efficiency of ventilation.
Decreased tissue elasticity renders the lungs less capable of expanding during inhalation and less capable of bouncing back during exhalation.
Decreased muscle mass will make the diaphragm and intercostal muscles weaker and less capable of expanding and contracting the chest cavity.
Combined, these changes increase the work of breathing, meaning it takes more effort to breathe, and this is especially true during physical activity.
Another effect of aging is an increased risk of respiratory infections. This is due to the decreased ventilatory efficiency along with a decreased ability to cough forcefully enough to clear lung secretions.
Immobility that often occurs with aging also adds to the respiratory infection risk. Finally, the immune system becomes less effective in fighting off infections.All right, as a quick recap… The respiratory system consists of the lungs and the structures that make up the “airway.” Air enters through either the nose or the mouth, making its way to the pharynx and then the larynx, followed by the trachea, where it branches off to the left and right bronchi, which divide off in the lungs into smaller bronchioles that end in clusters of alveoli.

Recap5:11–6:10

The respiratory system specifically functions in respiration, which involves two processes: ventilation, which is the mechanical process of moving air into and out of the lungs, and gas exchange, which is the process by which inhaled oxygen enters the blood from the alveoli, and carbon dioxide exits the blood into the alveoli to be exhaled.
Decreased tissue elasticity, muscle mass, and immune system effectiveness associated with aging all contribute to decreased efficiency of ventilation and increased risk of respiratory infections.