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,
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
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
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.
How Do the Lungs and Respiratory System Work?
The cells in our bodies need oxygen to stay alive. Carbon dioxide is made in our
bodies as cells do their jobs.
The lungs and respiratory system allow oxygen in the air to be taken into the body,
while also letting the body get rid of carbon dioxide in the air breathed out.
When you breathe in, the diaphragm moves downward toward the abdomen, and the rib
muscles pull the ribs upward and outward. This makes the chest cavity bigger and pulls
air through the nose or mouth into the lungs.
In exhalation, the diaphragm moves upward and the chest wall muscles relax, causing
the chest cavity to get smaller and push air out of respiratory system through the
nose or mouth.
Every few seconds, with each inhalation, air fills
a large portion of the millions of alveoli. In a process called diffusion, oxygen
moves from the alveoli to the blood through the capillaries (tiny blood vessels) lining
the alveolar walls. Once in the bloodstream, oxygen gets picked up by the in red blood cells. This oxygen-rich blood
then flows back to the heart, which pumps it through the arteries to oxygen-hungry
tissues throughout the body.
In the tiny capillaries of the body tissues, oxygen is freed from the hemoglobin
and moves into the cells. Carbon dioxide, made by the cells as they do their work,
moves out of the cells into the capillaries, where most of it dissolves in the plasma
of the blood. Blood rich in carbon dioxide then returns to the heart via the veins.
From the heart, this blood is pumped to the lungs, where carbon dioxide passes into
the alveoli to be exhaled.