VMBO Year 2 · HAVO/VWO Years 2–3 · Cellular respiration and breathing · Section 1.4

Breathing

Gas exchange

Inhaled and exhaled air have different compositions. Exhaled air normally contains less oxygen, more carbon dioxide and more water vapour than inhaled air.

Gas exchange occurs in the alveoli: oxygen moves from the air into the blood, while carbon dioxide moves from the blood into the air.

Exchange is efficient because alveoli have thin walls and a large total surface area. Blood arriving at the lungs has relatively little oxygen and more carbon dioxide; after gas exchange, it contains more oxygen and less carbon dioxide.

Chest breathing

During chest breathing, the intercostal muscles between the ribs move the ribs and sternum.

When breathing in, the ribs and sternum move upwards and outwards. The chest cavity becomes larger, pressure in the lungs falls, and air flows in.

During quiet breathing out, these muscles relax. Elastic recoil makes the chest and lungs smaller, and air flows out.

Diaphragmatic breathing

During diaphragmatic breathing, the diaphragm contracts and moves downwards. This enlarges the chest cavity and draws air into the lungs.

The abdominal organs are displaced slightly, causing the abdominal wall to move outwards. During breathing out, the diaphragm relaxes and moves upwards as the chest cavity becomes smaller.

Breathing muscles

The breathing muscles include the diaphragm and intercostal muscles. Abdominal muscles contribute to forced breathing out, while muscles near the collarbones and neck can assist deeper breathing in.

Chest and diaphragmatic movements work together during normal breathing.