A net, cast in seconds
How Does a Cut Stop Bleeding?
Bleeding stops because your blood builds a mesh across the hole and catches its own cells in it.
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Step 1 of 5
The vessel squeezes itself shut first.
Within seconds of being cut, muscle in the vessel wall clamps down, narrowing the pipe and slowing the flow before anything else can happen.
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Step 2 of 5
Sticky fragments pile into the gap.
Platelets are cell fragments that normally slide past smooth vessel walls. Torn edges are not smooth, so they stick, then call more platelets to join them.
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Step 3 of 5
Then a mesh is spun across the hole.
A chain of chemical steps ends with soluble protein turning into long insoluble threads. They criss-cross the gap into a net in about five minutes.
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Step 4 of 5
Blood cells get caught, and it dries.
Red cells snag in the net and the whole thing contracts, squeezing fluid out and pulling the wound edges together. Dried, that is a scab.
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Step 5 of 5
The real repair happens underneath.
The scab is only a lid. Beneath it new skin creeps in from the edges, and when it meets in the middle the scab has nothing left to hold on to and falls off.
The clotting cascade has more than a dozen steps, and each one activates many copies of the next — so a tiny trigger becomes a full net in minutes.
The short version
Bleeding stops when the vessel clamps, platelets plug the tear, and a protein mesh catches blood cells into a clot that dries into a scab.
Try it yourself
Watch a small cut over a few minutes. It stops looking wet before it looks solid — the net forms before it dries.
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