Take a deep breath right now. Feel your chest expand, your ribs move outward, your diaphragm pull downward. 🫁 In this single moment, you just changed the pressure in your thoracic cavity, drew in 500 millilitres of air, and set up a gas exchange at millions of tiny air sacs in your lungs. The oxygen entering your blood and the carbon dioxide leaving it — this happens over 20,000 times a day. Avinto will walk you through every detail of Subtopic 6.2: Gas Exchange in Mammals — structures, mechanisms, and controlling factors. 🔬 Type START!