Volume & Pressure Changes in the Lungs | Biology for GCSE/IGCSE - Year 11 PDF Download

Volume & Pressure Changes in the Lungs

• The diaphragm is a thin muscle separating the chest cavity from the abdomen and is crucial for controlling lung ventilation.
• When the diaphragm contracts, it flattens, increasing the chest cavity (thorax) volume, which lowers air pressure inside the lungs relative to outside the body, drawing air in.
• When the diaphragm relaxes, it returns to its domed shape, decreasing the chest cavity (thorax) volume, which raises air pressure inside the lungs relative to outside the body, forcing air out.
• The external and internal intercostal muscles function as antagonistic pairs, working in opposite directions to each other.
• During inhalation, the external intercostal muscles contract to pull the ribs up and out:
  • This action increases the volume of the chest cavity (thorax), decreasing air pressure and drawing air in.
• During exhalation, the external intercostal muscles relax, allowing the ribs to drop down and in:
  • This action decreases the volume of the chest cavity (thorax), increasing air pressure and forcing air out.
• When there is a need to increase the rate of gas exchange, such as during strenuous activity, the internal intercostal muscles also work to pull the ribs down and in, decreasing the volume of the thorax more significantly, thus forcing air out more forcefully and quickly. This process is known as forced exhalation.
  • This action is crucial because there is a greater need to expel the increased levels of carbon dioxide produced during strenuous activity.
• This mechanism allows a greater volume of gases to be exchanged, meeting the increased oxygen demand and carbon dioxide removal requirements of the body during intense physical activity.