Summary
Diaphragm and intercostal muscles change thorax volume and pressure to move air in and out.
In depth
Inspiration: diaphragm contracts and flattens, external intercostals raise ribs, volume rises, pressure falls, air enters. Expiration at rest is passive recoil. Tidal volume is about 500 mL; vital capacity 4 to 5 L.
Pressure changes follow Boyle's law. Elastic recoil assists exhalation. Forced breathing uses internal intercostals and abdominal muscles.
Remember: air moves from high to low pressure.
Quiet inspiration is active, using the diaphragm (about 75 percent of the effort) and external intercostals, increasing thoracic volume and lowering intrapleural pressure (about minus 5 to minus 8 cm of water), which expands the lungs through pleural adhesion. Quiet expiration is passive due to elastic recoil, while forced breathing uses internal intercostals and abdominal muscles. Boyle's law links volume and pressure. A pneumothorax (air in the pleural space) causes lung collapse.
Lung volumes include tidal volume (500 mL), inspiratory and expiratory reserve volumes, residual volume (about 1.2 litres) that cannot be exhaled, and vital capacity (about 4 to 5 litres), measured by spirometry. Minute ventilation equals tidal volume times rate. Asthma and COPD reduce airflow, shown by lower FEV1.
Remember: air moves because of pressure differences made by changing chest volume.
Frequently asked questions
What is Breathing Mechanism?
Diaphragm and intercostal muscles change thorax volume and pressure to move air in and out.
Which area of biology covers Breathing Mechanism, and how advanced is it?
Breathing Mechanism is one of the 51 topics in Human Physiology. It is rated Intermediate, so it suits learners who already know the core vocabulary. Related topics in this area include Respiratory System, Circulatory System, Lung Compliance and Surfactant.
Can you give an example of Breathing Mechanism?
Asthma narrows airways.
What should I learn before Breathing Mechanism?
Work through the Beginner topics in Human Physiology first, such as Homeostasis, Tissues and Organs, Skeletal System, then return to Breathing Mechanism. Intermediate topics assume the Beginner vocabulary.
What topics are related to Breathing Mechanism?
The closest topics to Breathing Mechanism are Respiratory System, Circulatory System, Lung Compliance and Surfactant, Fluid Compartments. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand Breathing Mechanism?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for Breathing Mechanism. To practise the whole of Human Physiology, use the Human Physiology quiz.
How is Breathing Mechanism different from Respiratory System?
Breathing Mechanism: Diaphragm and intercostal muscles change thorax volume and pressure to move air in and out. Respiratory System: Airways and lungs that bring oxygen in and remove carbon dioxide. Read both side by side and note what each one explains.
How should I study Breathing Mechanism step by step?
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Respiratory System and explain the difference aloud. Finally, take the Human Physiology quiz and come back to this page for any question you miss.