The human lungs contain between 274 and 790 million alveoli, small air sacs where oxygen from inhaled air is transferred to the bloodstream, according to Encyclopédie Universalis and Kenhub. These alveoli create a gas exchange surface area larger than 70 square meters, which is comparable to the size of an official badminton court—just over 81 square meters. This immense surface area is made possible by the alveolar-capillary membrane, a structure only about one micrometer thick, allowing for a nearly instant transfer of gases between air and blood. Each alveolus is coated with a substance called surfactant, produced by specialized cells known as type 2 pneumocytes. This surfactant prevents the alveoli from collapsing and occupies a volume of about 35 milliliters. The number of alveoli varies between individuals, with estimates ranging from 274 to 790 million, depending on factors such as age and health. A theoretical calculation suggests that with around 600 million alveoli in total and each having a surface area of 0.125 square millimeters, the total exchange surface area approaches 75 square meters. The alveoli are not randomly distributed but are organized into structures called acini, each containing approximately 1,200 alveoli. These acini are connected by microscopic openings known as Kohn pores, which are about 3 micrometers in diameter. These tiny passages help maintain pressure balance within the lung tissue, ensuring efficient gas exchange. The amount of blood flowing through the capillaries surrounding the alveoli is relatively small, not exceeding 75 to 100 milliliters at any given time. The human body constantly requires oxygen to sustain all its cells, organs, and muscles, even when at rest. This massive exchange of oxygen and carbon dioxide is only possible thanks to the vast surface area provided by the alveoli. Without this intricate system, it would be impossible to absorb enough oxygen to support the body's vital functions.