Ventilation

• The flow of air in and out of the alveoli is referred to as ventilation and is composed of two stages; inspiration and expiration. This process occurs with the help of two sets of muscles, the intercostal muscles and diaphragm
• 1. During inspiration, the external intercostal muscles contract whereas the internal ones relax, as a result cause the ribs to raise upwards.
• 2) The diaphragm contracts and flattens
• 3) In combination, the intercostal muscles and diaphragm cause the volume inside the thorax to increase, thus lowering the pressure
• 4) The difference between the pressure inside the lungs and atmospheric pressure creates a gradient, thus causing the air to enter the lungs
• 5) During expiration, the internal intercostal muscles contract whereas the external ones relax therefore lowering the rig cage
• 6) The diaphragm relaxes and rises upwards
• 7) These actions in combination decrease the volume inside the thorax, therefore increasing the pressure, forcing the air out of the lungs