The digestive system comprises several primary organs: the mouth, esophagus, stomach, small and large intestines, and anus. Some of these are necessary parts of a functioning digestive system, so I don't know that it is possible to call one of them the most important.

For example, the mouth is obviously important because it is the entrance for food into the body, a process without which the other organs would not have purpose. The mouth is also where the first processes of digestion take place, both through chewing and chemical processes from saliva. Toward the other end of the system, the nutrients of the food are absorbed in the intestines. Others can be removed, and can therefore be considered less important. For example, the esophagus is essentially just a tube connecting the mouth to the stomach. It is possible to remove an esophagus and essentially connect the mouth directly to the stomach (though some muscles are removed as well, so this is not an exact replacement). Perhaps counter-intuitively, the stomach is not a necessary organ.

Removal of the entire stomach is one (extreme) treatment for stomach cancer, but is survivable because food can be moved in very small quantities directly to the small intestine. There are also several accessory organs which help with digestion, but are not considered part of the digestive tract. Of these, the pancreas and gallbladder are not necessary, so they can probably be considered less important as well. Life without them tends to be complicated and unpleasant though. The pancreas produces insulin, necessary for regulating blood sugar. It is possible to survive by taking insulin injections though. The gallbladder stores bile that helps to digest food. Without it, bile continuously enters into the digestive system. This can make digestion of some foods more difficult, but is quite survivable.

All of the organs in the digestive system are very important but if I had to choose one, it would probably be the small intestine.

After food gets broken down in the stomach, it travels to the small intestine, which is about 20 feet long and helps with the body’s absorption of nutrients. Without it, many of the nutrients we eat in our food wouldn’t get absorbed into our cells, which is a process we need to survive!

There’s not just one organ that is really important in the digestive system - it’s really composed of the mouth, oesophagus, stomach, your small and large intestine, and the anus. All of these organs are necessary for us to digest food! If you have to pick one though, I would say your stomach! Learn more here:

There isn't really a most important organ. The stomach and intestines have different roles in digestion, and without both, digestion doesn't happen.

It’s hard to say, since they all work together to break down food so your body can use it as fuel! For example, without the stomach there would be nothing to dissolve the solid food into something your intestines can process, but without your intestines you would not be able to absorb any nutrients. I think you would have to say they are all equally important. It is sort of like how all the parts of a car work together to make it move!