Respiratory system: Structure and function

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. 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. 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.

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.