Breathing Mechanics
Muscles change lung volume to move air.
About this topic
Breathing works by changing the volume and pressure in the chest. On inhaling, the intercostal muscles contract to lift the ribs and the diaphragm contracts and flattens, increasing chest volume and decreasing pressure so air flows in. On exhaling, they relax, volume decreases, pressure rises and air flows out.
Breathing rate is controlled by the brain, which monitors CO₂ levels in the blood. Exercise increases both rate and depth. Lung capacity can be measured by spirometry.
Think of a bell jar model: pull down the rubber sheet at the base, volume rises, pressure drops and air rushes in to the balloons. In the body, when the diaphragm flattens and ribs move up and out, air pressure inside falls below atmospheric pressure and air flows in. Exhaling at rest is largely passive, as the muscles relax and the elastic lungs recoil.
During exercise, extra muscles in the abdomen and between the ribs help force air out. Mouth-to-mouth resuscitation works by pushing air in, the opposite way to normal breathing. Breathing rate is controlled by the brain, which detects rising carbon dioxide, not low oxygen, in the blood. This is why holding your breath becomes uncomfortable. Students often say the lungs suck air in; actually air is pushed in by higher outside pressure.
Key ideas
- Inhale: diaphragm contracts and moves down
- Exhale: it relaxes
- Pressure follows Boyle's law
Quick check
Use cases: where Breathing Mechanics helps
- Homework: review the key idea behind Breathing Mechanics before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Breathing Mechanics without notes.
- Visual learning: play with the interactive lab to see how Breathing Mechanics changes when you adjust its inputs.
- Teaching a friend: explain Breathing Mechanics in your own words, then compare your version with the key ideas.
Biology underpins medicine, farming, conservation and biotechnology.
Frequently asked questions
What is Breathing Mechanics?
Muscles change lung volume to move air.
What will I learn in Breathing Mechanics?
Inhale: diaphragm contracts and moves down. Exhale: it relaxes. Pressure follows Boyle's law.
Is Breathing Mechanics part of Biology?
Yes. It is one of 150 Biology topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the Breathing Mechanics lab work on a phone or tablet?
Yes. The animation resizes to fit your screen and supports touch, so you can drag, tap and slide with your finger.
How should I study Breathing Mechanics?
Read the summary and key ideas first, play with the interactive lab to see the idea in motion, then answer the quick check. If you get a question wrong, go back to the key idea it tests.
Do I need an account, and is my progress saved?
No account is needed. Marking a topic as learned is saved in your own browser, so it stays on that device and is not sent to a server.