The Respiratory System

Aerobic respiration requires gaseous exchange. The term ‘gaseous‘ relates to gases, while ‘exchange‘ signifies a transfer or the act of giving and taking.

The two gases exchanged in the respiratory system are oxygen and carbon dioxide. The respiratory system contains organs that allow us to get the oxygen we need, and it removes carbon dioxide, a waste product that we don’t need.

The respiratory system contains:

  • Two lungs, located in the chest (thorax) and protected by 12 pairs of ribs
  • Tubes that lead from the entrance (mouth and nose) to the lungs
  • Various structures in the chest facilitate the movement of air in and out of the lungs.

Air Travelling Through the Respiratory System

1. We take air in through our nose and mouth.

2. This air goes down the trachea (also known as the windpipe), towards the lungs.

  • The trachea contains rings of cartilage that prevent it from collapsing when we inhale

3. Once the air reaches the lungs, it moves into two smaller tubes called bronchi.

  • Each lung has one bronchus

4. The bronchi split into smaller tubes called bronchioles through which the air travels.

5. At the end of each bronchiole, the air ends up in microscopic air sacs called alveoli.

  • Each lung contains hundreds of millions of alveoli

Ventilation

The process of ventilation (breathing), involves the movement of:

  • Ribs – Bones that protect the respiratory system
  • Intercostal muscles – Muscles between the ribs
  • The diaphragm – A smooth, dome-shaped muscle located at the bottom of the ribcage

Inhalation (Breathing in)

When we inhale, the diaphragm and intercostal muscles contract, causing the ribcage to move outwards and upwards. This action increases the volume of the thorax, therefore decreasing its pressure.

At this point, the pressure in the lungs is lower than outside the body. To equalise this pressure, air is drawn into the lungs.

Exhalation (Breathing out)

When we exhale, the diaphragm and intercostal muscles relax, causing the ribcage to move downwards and inwards. This action decreases the volume of the thorax, therefore increasing its pressure.

At this point, the pressure in the lungs is greater than outside the body. To equalise this pressure, the air is forced out of the lungs.

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