Respiratory System Glossary

What Does This Respiratory Glossary Cover?

This glossary covers the structures of the airway and lungs, the muscles that move air, and the key words used to describe how gas exchange works. Terms are grouped from A to Z, and each one links to the page of our site that explains it in full, starting from the overview of the respiratory system.

Terms with their own in-depth pages

• Lung lobes are the separate sections of each lung, divided by deep grooves called fissures: three in the right lung and two in the left.
• Nostrils, or external nares, are the two outer openings of the nose, where air first enters the airway.
• Choanae, or internal nares, are the two back openings of the nasal passages, where the nasal cavity opens into the throat.
• The nasopharynx is the upper part of the pharynx, behind the nasal cavity, and the only part of the throat that carries air alone.
• The oral cavity, or mouth, is the secondary entrance to the respiratory tract, used when the nose is blocked or more air is needed.
• The intercostal muscles are the layers of muscle between the ribs that move the rib cage and are vital to breathing.

Respiratory System Terms A to F

Terms from A to F name the deepest parts of the airway, the reflex guards at its entrance and the main breathing muscle.

Alveoli

Tiny, thin-walled air sacs at the ends of the smallest airways, about 300 to 500 million in an adult, where oxygen enters the blood and carbon dioxide leaves it.

Bronchi

The two main airways that branch from the trachea into the right and left lungs, then divide into smaller lobar and segmental bronchi to form the bronchial tree.

Bronchioles

Small airways about 1 mm wide or less, with no cartilage in their walls, that carry air from the bronchi toward the alveoli.

Carina

The ridge of cartilage at the lower end of the trachea where it splits into the two main bronchi; its lining is very sensitive and triggers coughing.

Cilia

Microscopic hair-like projections on the cells lining the nasal cavity and airways that beat in waves to sweep mucus and trapped particles toward the throat.

Diaphragm

The dome-shaped sheet of muscle under the lungs that separates the chest from the abdomen; it contracts and flattens to draw air in and is the main muscle of breathing.

Epiglottis

A leaf-shaped flap of elastic cartilage at the top of the larynx that folds back during swallowing to keep food and drink out of the airway.

Respiratory System Terms G to N

Terms from G to N cover gas exchange itself, the voice box, the cleaning system of the airways and the parts of the nose.

Gas exchange

The movement of oxygen from the alveoli into the blood and of carbon dioxide from the blood into the alveoli by diffusion; it is the most important of the respiratory system functions.

Glottis

The vocal folds of the larynx together with the gap between them, called the rima glottidis; it opens for breathing and closes for swallowing and speaking.

Goblet cells

Cup-shaped cells in the lining of the nose, trachea and bronchi that release mucus to trap dust and microbes.

Hilum

The wedge-shaped doorway on the inner surface of each lung where the main bronchus, pulmonary vessels, nerves and lymph vessels enter and leave.

Larynx

The voice box: a tube of cartilages in the front of the neck that connects the pharynx to the trachea, protects the airway and holds the vocal folds.

Lungs

The two spongy organs in the chest where breathing ends in gas exchange; the right lung has three lobes and the left lung has two.

Mucociliary escalator

The cleaning system of the airways, in which mucus traps particles and cilia carry it up to the throat to be swallowed or coughed out.

Nasal cavity

The air-filled space behind the nose, divided in two by the nasal septum, that filters, warms and moistens inhaled air and holds the receptors for smell.

Nasal conchae

Three curled shelves of bone on each side wall of the nasal cavity, also called turbinates (superior, middle and inferior), that make inhaled air swirl over the moist lining.

Nasal meatus

Each of the air channels under a concha, the superior, middle and inferior meatus, into which the sinuses and the tear duct drain.

Nose

The external organ of the face made of bone and cartilage that houses the nostrils and forms the main entrance to the airway.

Respiratory System Terms P to Z

Terms from P to Z describe the air-filled spaces around the nose, the throat and windpipe, the lining of the lungs and how much air one breath moves.

Paranasal sinuses

Four pairs of air-filled spaces in the frontal, maxillary, ethmoid and sphenoid bones that open into the nasal cavity, lighten the skull and add resonance to the voice.

Pharynx

The throat: a muscular tube behind the nose and mouth, divided into the nasopharynx, oropharynx and laryngopharynx, that carries air to the larynx and food to the esophagus.

Pleura

The two-layered membrane around each lung; the visceral pleura covers the lung, the parietal pleura lines the chest wall, and a thin film of fluid between them lets the lung glide.

Surfactant

A mix of phospholipids and proteins made by type II pneumocytes that lowers surface tension inside the alveoli so they do not collapse when we breathe out.

Tidal volume

The amount of air moved in or out with one normal, quiet breath, about half a liter in an adult.

Trachea

The windpipe: a tube about 10 to 12 cm long, held open by 16 to 20 C-shaped rings of cartilage, that runs from the larynx to the main bronchi.

Vocal folds

Two bands of muscle and tissue inside the larynx, also called vocal cords, that vibrate as air passes between them to produce the voice.

How Does Air Move Through the Respiratory System?

Air moves through the respiratory system in one line, from the nostrils to the alveoli, and the glossary terms follow that path in order. Every structure from the nostrils down to the larynx belongs to the upper respiratory tract, and every structure from the trachea down belongs to the lower respiratory tract.

1. Air enters through the nostrils, or through the oral cavity when the nose is blocked.
2. It flows through the nasal cavity, where the conchae and meatuses warm, moisten and filter it.
3. It leaves the nasal cavity through the choanae and passes down the nasopharynx and the rest of the pharynx.
4. It passes the epiglottis and the glottis of the larynx and enters the trachea.
5. At the carina it divides into the two main bronchi, which branch into ever smaller bronchioles inside the lung lobes.
6. It reaches the alveoli, where gas exchange takes place, while the diaphragm and intercostal muscles power each breath.

Explained simply

Picture a busy highway that starts at two front doors, the nostrils, and ends in millions of tiny parking spaces, the alveoli. Along the way, air is cleaned at checkpoints, warmed in the nasal cavity and sorted at junctions such as the carina. Most of the words in this glossary are simply names for the stops along that road.