Because at some point our organs get tired and weak from all the years of pumping and circulation etc. so at some point our bodies just can't do that forever...
To begin, when a human chewing it's food, it's called mechanical digestion. Thousands of receptors on you're tongue react correspondingly to what chemicals are present. For instance foods that are very savory or sweet produce more saliva. These impulses tell your brain to over active salivary glands. This also can start cravings. Such as foods artificially produced with chemicals that will make your brain act the same way.
Once the food is chewed, it may be swallowed. The food then travels down the pharynx. The pharynx is tube that connects the oral cavity to either the esophagus or larynx. The Epiglottis is a flap that can cover either hole. If you are breathing air, it will cover the esophagus. If you are swallowing food, it will cover the larynx.
Once the food has been swallowed, passing through the pharynx it enters the esophagus. It has specials muscles that help plunge the food down the throat, which prevents choking. The food will then enter the stomach.
The stomach is special because it contains gastric acid. The stomach uses it for a process known as chemical digestion. It breaks down macromolecules, which can be used as energy. The stomach is lined with muscles so it can churn, evenly breaking down the food.
The stomach may then open its pyloric sphincter. This sphincter connect to the small intestine. At this point, the "food" can now be called feces. Through the journey of the small intestine, it will mostly be getting nutrients sucked out of it. This intestine does alot of the work. It has muscles around it to push the feces thought out it. The feces may then enter the large intestine, aka the colon. At this stage, the person may voluntary force the bowl muscles to contact. This will push the feces out. It will then meet the sphincter, which will open and close once the process is completed. This is a basic understanding of how the digestive system works.
Hope this could help!
