system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:What does our body do when we go to sleep. Does it enter some kind of maintenance mode?

Like does our heart slower down to a 'resting' peace
Our breathing pattern change from our every day pattern etc..etc..
gpt
**TL;DR- The primary reason we sleep is so our brains can clean themselves.**










The human brain weighs only 3lbs, but it uses 20% of its body's energy. Because it uses so much energy, it produces a lot of metabolic waste. Our body gets rid of metabolic waste through something known as the lymphatic system. It essentially just transports chemical waste to your urine. The brain is too special to use the lymphatic system. It has its own cleaning system known as the glymphatic system. While we sleep our brain cells clump together, losing 60% of the brain's volume. Then spinal fluid is pumped through the brain to get rid of toxins that accumulated throughout the day. These toxins are then moved into the lymphatic system and removed with the rest of the body's waste.






Failure to sleep will result in an accumulation of toxins in the brain, like beta amyloid ( the compound that causes Alzheimer ). Within the first few days with little sleep, your frontal cortex with begin to slow down processing, you will fly in and out of focus, and simple mental tasks will become strenuously difficult. By day 4 with little, to no sleep, you will begin hallucinating and your executive function will become severely impaired. 




There have been a limited number of experiments involving humans to stay up for unnaturally long periods of time. However, we do have a fair amount of experiments done on rats. In 1989, at Rochester University, researchers kept 10 rats awake to see what would happen. All the rats died with 32 days of sleep deprivation ( the first one died on day 11). The exact number of days it would take to kill a human is unknown, and is dependant on an individual's health before experiencing extended sleep deprivation, though it is known that eventually it will result in death. 









On the surface, sleep doesn't make sense. It makes us lose productivity, and makes us vulnerable to predators. Yet all mammals, birds, reptiles, and even fish sleep in some way or form. Evolution wouldn't sustain this trait unless it is absolutely necessary to a species's survival. It is. It prevents our brains from drowning in metabolic waste.