The Respiratory System

Aerobic respiration requires gaseous exchange and we can break this down into two parts. Gaseous is related to gases and exchange is related to giving and taking (a transfer).

The two gases exchanged in the respiratory system are oxygen and carbon dioxide. It contains organs that allow us to get the oxygen we need and It removes carbon dioxide as waste 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
  • Different structures in the chest allow air to move 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 which prevent it from collapsing when we inhale

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

  • There is one bronchus in each lung

4. The bronchi split into smaller tubes called bronchioles, which the air passes into

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 – The bones protecting the respiratory system
  • Intercostal muscles – Muscles between the ribs
  • The diaphragm – Smooth muscle at the bottom of the ribcage

Inhalation (Breathing in)

When we inhale air, the diaphragm and intercostal muscles contract. So, the ribcage moves outwards and upwards. The volume of the thorax increases, which decreases the pressure of the thorax.

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 air, the diaphragm and intercostal muscles relax. So, the ribcage moves downwards and inwards. The volume of the thorax decreases, which increases the pressure of the thorax.

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.