Lungs and Respiratory System
What Are the Lungs and Respiratory System?
The lungs and respiratory system allow us to breathe. They bring oxygen into our bodies (called inspiration, or
inhalation) and send carbon dioxide out (called expiration, or exhalation).
This exchange of oxygen and carbon dioxide is called respiration.
What Are the Parts of the Respiratory System?
The respiratory system includes the nose, mouth, throat, voice box, windpipe, and lungs.
Air enters the respiratory system through the nose or the mouth. If it goes in the nostrils (also called nares), the
air is warmed and humidified. Tiny hairs called cilia (pronounced: SIL-ee-uh) protect the nasal passageways
and other parts of the respiratory tract, filtering out dust and other particles that enter the nose through the
breathed air.
The two openings of the airway (the nasal cavity and the mouth) meet at the pharynx (pronounced: FAR-inks),
or throat, at the back of the nose and mouth. The pharynx is part of the digestive system as well as the
respiratory system because it carries both food and air.
At the bottom of the pharynx, this pathway divides in two, one for food — the esophagus (pronounced:
ih-SAH-fuh-gus), which leads to the stomach — and the other for air. The epiglottis (pronounced:
eh-pih-GLAH-tus), a small flap of tissue, covers the air-only passage when we swallow, keeping food and liquid
from going into the lungs.
The larynx, or voice box, is the top part of the air-only pipe. This short tube contains a pair of vocal cords,
which vibrate to make sounds.
The trachea, or windpipe, is the continuation of the airway below the larynx. The walls of the trachea
(pronounced: TRAY-kee-uh) are strengthened by stiff rings of cartilage to keep it open. The trachea is also
lined with cilia, which sweep fluids and foreign particles out of the airway so that they stay out of the lungs.
At its bottom end, the trachea divides into left and right air tubes called bronchi (pronounced: BRAHN-kye),
which connect to the lungs. Within the lungs, the bronchi branch into smaller bronchi and even smaller tubes
called bronchioles (pronounced: BRAHN-kee-olz). Bronchioles end in tiny air sacs called alveoli, where the
exchange of oxygen and carbon dioxide actually takes place. Each person has hundreds of millions of alveoli
in their lungs. This network of alveoli, bronchioles, and bronchi is known as the bronchial tree.
The lungs also contain elastic tissues that allow them to inflate and deflate without losing shape. They're
covered by a thin lining called the pleura (pronounced: PLUR-uh).
The chest cavity, or thorax (pronounced: THOR-aks), is the airtight box that houses the bronchial tree, lungs,
heart, and other structures. The top and sides of the thorax are formed by the ribs and attached muscles, and
the bottom is formed by a large muscle called the diaphragm (pronounced: DYE-uh-fram). The chest walls
form a protective cage around the lungs and other contents of the chest cavity.