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Quite a simple thing when you think of it. Our bodies are only so large, and can only store so much waste. Whatever we eat undergoes mechanical digestion in the mouth with the teeth and saliva. It then travels to the stomach where enzymes break it down further in mechanical digestion. Once in reaches the small intestines, it goes through chemical digestion, where polymers are broken down into monomers. At this point, the kidney takes whatever it thinks the body needs and dumps everything it doesn't need or has already used. All this excess waste travels to the large intestine, where it turns into feces and urine. The urine contains all of the used liquids we no longer can use for benefit, and the feces is, well... the waste that is simply solid material unable to be converted into energy or has already gone through the process. All the waste lies in the rectum, and the rectum is only so large, and will eventually fill up. When this time comes, your body sends a signal to your brain to empty your rectum, and you excrete feces. On the other hand, the urine fills up in the bladder, and sits there for quite a while until your bladder fills up as well. Your excretory system has both voluntary and involuntary reactions. You don't always have to think to keep your rectum closed, but you can choose to open it in a time of need. That is why you have to excrete body wastes; to remove excess material consuming the body's capacity.

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15y ago

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