Right now im learning about Prana and Apana. . . . The body’s pathways for nutrients and waste are not as simple as those of a cell, but they are not so complex that you can’t grasp the concepts as easily. a simplified version of the nutritional and waste pathways is the picture above. It shows how the human system is open at the top and at the bottom. You take in prana, nourishment, in solid and liquid form at the top of the system: It enters the alimentary canal, goes through the digestive process, and after a lot of twists and turns, the resulting waste moves down and out. It has to go down to get out because the exit is at the bottom. So, the force of apana, when it’s acting on solid and liquid waste, has to move down to get out. You also take in prana in gaseous form: The breath, like solid and liquid nutrition, enters at the top. But the inhaled air remains above the diaphragm in the lungs where it exchanges gases with the capillaries at the alveoli. The waste gases in the lungs need to get out—but they need to get back out the same way they came in. This is why it is said that apana must be able to operate freely both upward and downward, depending on what type of waste it’s acting on. That is also why any inability to reverse apana’s downward push will result in an incomplete exhalation. The ability to reverse apana’s downward action is a very basic and useful skill that can be acquired through yoga train- ing, but it is not something that most people are able to do right away. Pushing downward is the way that most people are accustomed to operating their apana because whenever there’s anything within the body that needs to be disposed, humans tend to squeeze in and push down. That is why most beginning yoga students, when asked to exhale completely, will squeeze in and push down their breathing muscles as if they’re urinating or defecating.