About Lungs & Breathing
The respiratory system brings oxygen into the body and removes carbon dioxide. Air travels through branching airways into millions of tiny air sacs called alveoli, where gases move between the air and nearby capillary blood.
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Airways
Air enters through the nose or mouth and travels down branching tubes.
Learn MoreAlveoli
Millions of tiny alveoli create a huge surface area for gas exchange.
Learn MoreDiaphragm
The diaphragm is the major muscle used for quiet breathing.
Learn MoreOxygen Transport
Oxygen entering blood attaches mostly to hemoglobin in red blood cells.
Learn MoreCarbon Dioxide
Carbon dioxide is a waste product of normal cellular metabolism.
Learn MoreBreathing Control
The brainstem automatically adjusts breathing.
Learn MoreBreathing and Voice
Exhaled air provides the energy for speech and singing.
Learn MoreSeeing the Lungs
X-rays, CT scans, and other imaging methods let doctors examine lungs without surgery.
Learn MoreAirways
The trachea divides into two main bronchi, one for each lung. The bronchi repeatedly branch into smaller bronchioles. Cilia and mucus help trap particles and move them upward toward the throat.
Alveoli
Their walls are extremely thin and lie beside tiny capillaries. Oxygen moves from inhaled air into blood, while carbon dioxide moves from blood into the alveoli to be exhaled.
Diaphragm
When it contracts, it moves downward and increases the volume of the chest. Air flows into the lungs. When it relaxes, elastic tissues help the lungs recoil and air moves outward.
Oxygen Transport
The heart then pumps oxygen-rich blood throughout the body. Cells use oxygen during many energy-producing reactions, though cells can also perform some processes without oxygen.
Carbon Dioxide
Blood transports carbon dioxide back toward the lungs in several chemical forms. Exhaling removes it from the body and helps keep blood acidity within a narrow range.
Breathing Control
Sensors in the body monitor carbon dioxide, acidity, oxygen, and stretch. The nervous system changes breathing rate and depth during exercise, sleep, speaking, emotion, and changes in altitude.
Breathing and Voice
Air passing through the larynx can vibrate the vocal folds. The throat, mouth, tongue, lips, and nasal passages then shape the sound into speech.
Seeing the Lungs
A chest X-ray can show the lungs, heart, ribs, diaphragm, and large airways. CT provides much more detailed cross-sectional images when needed.