Published by Australian Academy of Science
Activity 1 | The rise and rise of asthma

Structure and function of the human breathing system

Asthma involves changes to both the structure and function of various parts of the breathing system.

1. List the main organs or components that make up the human breathing system.

2. Describe the function of each organ or component.

3. Name a structural feature of each organ or component that helps it carry out its functions.

4. During an asthma attack, which components of the respiratory system are affected? How do these changes alter the function of the breathing system?

Teachers notes

1. The main components of the breathing system are:
   
   • nasal passages;
     
   • pharynx;
     
   • larynx (voice box);
     
   • trachea (wind pipe);
     
   • bronchi;
     
   • bronchioles (lungs);
     
   • alveoli (airsacs);
     
   • capillaries with red blood cells;
     
   • thoracic cavity (including diaphragm, ribs and intercostal muscles).

2. The functions of each component are:
   • nasal passages: warm, moisten and filter air;
     
   • pharynx: channels air to lungs and food and water to the stomach;
     
   • larynx: formation of sounds;
     
   • trachea: passage-way for air (windpipe from throat to lungs);
     
   • bronchi and bronchioles: air passages;
     
   • alveoli: gas exchange (especially carbon dioxide and oxygen);
     
   • capillaries with red blood cells: gas exchange;
     
   • thoracic cavity and diaphragm: ventilation (altering the volume of the chest cavity which changes the air pressure in the lungs).

3. Structural features of components that aid them in functioning effectively:
   • Nasal passages: hairs filter large particles; an abundance of capillaries in the nasal passages help to warm the incoming air.

   • Pharynx: gland cells produce mucus to trap particles.

   • Larynx: vocal cords (elastic ligaments) vibrate when air is directed against them and make sounds. The pitch of the sound is controlled by muscles changing the tension of the cords.

   • Trachea: has reinforcing rings of cartilage to protect the airway in the neck.

   • Bronchi, bronchioles: smooth muscle in the walls of these tubes can relax and contract. Relaxation dilates the lumen of bronchioles producing a larger air passage.

   • Alveoli: these sacs have a lining of thin flattened cells and are surrounded by capillaries facilitating gas exchange between the breathing system and the blood stream.

   • Capillaries and red blood cells: capillaries have thin walls to enable gas exchange. Red blood cells contain haemoglobin that picks up oxygen.

   • Thoracic cavity and diaphragm: the muscle fibres of the diaphragm, and those connected to the ribs, expand and contract to change the volume of the chest cavity.

1. During an asthma attack the smooth muscle of the bronchioles contract. This constricts the air passage and causes breathing difficulties.