system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is it that after getting blood drawn, and the needle gets pulled out of our arm, the hole left in our veins doesn't continuously leak blood into our bodies?

Does it just seal really quickly? Does some blood escape out of our veins and into our bodies?
gpt
The blood clots, or becomes hard at the site of an injury with the help of what are called platelets. This creates a temporary seal. Once this is complete, the platelets secrete what is called platelet-derived growth factor. This causes nearly connective tissue to undergo cell division and growth to permanently patch the hole.