system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How long does it take to our cells (like blood cells, muscles, etc...) to "understand" that we are dead after we made our last breath? Are white blood cells fighting against external agents minutes after we've died?
gpt
It depends on the tissues. Some tissues require a lot of oxygen and will expire relatively quickly, in a few minutes. Other tissues, like bones or skin, might last for hours, perhaps even a day.

Still other material, like sperm cells, could last longer than a day. 

You mentioned white blood cells, a fraction of these may actually live for days. 

However, you are unrecoverably dead after only a few minutes, and after a few days most of your tissues are going to be likewise unrecoverably dead.