Ouch!
Here's how platelets form clots. This small artery has a cut.
Blood flowing past the cut includes
red blood cells that carry oxygen,
platelets that come from
white blood cell fragments,
and clotting factors that help blood clot.
When a blood vessel is damaged, blood cells
and plasma ooze into surrounding tissue.
Platelets immediately stick to the edges of the
cut and release
chemicals that attract more platelets.
Eventually, a platelet plug is formed,
and the outside bleeding stops.
On the inside,
clotting factors cause a cascade of activity
that includes strands of blood-borne material
called fibrin
sticking together to seal the inside of the wound.
Eventually, the blood vessel heals,
and several days later, the blood clot dissolves.