VMBO Year 2 · HAVO/VWO Years 2–3 · Cellular respiration and breathing · Section 1.3
The respiratory system
The respiratory system
The respiratory system allows air to enter through the nose or mouth. Air passes through the pharynx, or throat, the larynx, or voice box, and the trachea, or windpipe, towards the lungs.
The trachea divides into two bronchi, which branch into smaller airways called bronchioles. Clusters of alveoli, or air sacs, lie at the ends of the smallest airways.
Below the lungs is the diaphragm, a sheet of muscle involved in breathing in and out.
The nasal and oral cavities
Breathing through the nose helps filter, warm and moisten the air. The nasal lining produces mucus that traps dust and microorganisms.
Nasal hairs catch larger particles. Cilia, tiny hair-like structures on cells, move mucus towards the throat, where it is swallowed. Smell receptors high in the nasal cavity detect odours in the air.
When you breathe through your mouth, the air is filtered, warmed and moistened less effectively.
The throat
The throat is a passage for both air and food. During breathing, the route to the airways remains open.
During swallowing, the soft palate and uvula help close the passage towards the nose, while the epiglottis and other protective movements help prevent food entering the airway.
If food or drink goes down the wrong way, it may enter the airway or pass towards the nose. Coughing can help clear material from the airway.
The trachea and lungs
The trachea is supported by C-shaped cartilage rings that keep it open. The bronchi also contain cartilage, while the smallest bronchioles have smooth muscle in their walls and no cartilage.
Mucus and cilia help keep the conducting airways clean. Alveoli are surrounded by networks of pulmonary capillaries.
The thin walls of the alveoli and capillaries allow oxygen and carbon dioxide to pass between air and blood. Together, the alveoli provide a very large exchange surface, often estimated at roughly 70–100 m² in adults, depending on measurement and lung inflation.
Glossary
- Bronchi
- The two main branches of the trachea carrying air into the lungs, supported by cartilage.
- Uvula
- The small projection at the back of the soft palate; the soft palate helps close the nasal passage during swallowing.
- Trachea
- The cartilage-supported tube carrying air from the larynx towards the bronchi.
- Alveoli
- Tiny lung air sacs where oxygen enters the blood and carbon dioxide leaves it.
- Pulmonary capillaries
- Tiny blood vessels surrounding the alveoli, where gas exchange occurs.
- Diaphragm
- A sheet of muscle separating the chest and abdominal cavities that moves during breathing.
- Nasal lining
- The mucus-producing lining that helps moisten, warm and filter inhaled air.
- Epiglottis
- A flap involved in protecting the entrance to the airway during swallowing.
- Cilia
- Tiny moving cell structures that carry mucus and trapped particles towards the throat.