When does your blood know when its the right time to form a clot?
Its supposed to happen only when blood leaves the body. If it happens in the vessels its a pretty bad idea to clot.
My first thought was it must be the contact to oxygen that triggers the clotting process. But thats nonsense since blood tranaports oxygen, right?
So how does your blood “know” its leaving the body?
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It doesn’t “know” there are platelets bonding with fibrin to create a barrier forming the clot. https://youtu.be/6taZMcj8co0
The default state of blood is clotting. Blood vessels secrete a chemical that inhibits clotting. Once the blood leaves the vessel the chemical is no longer present and the clotting process starts.
When you donate blood there is an anti-coagulant in the bag because even though there is no exposure to oxygen (vein -> needle -> tube -> bag) the blood will still clot if left on its own. Found that out when I had a blood donation fail partway through and it rendered what had been taken unusable because there was too much anti-coagulant in the bag for the volume of blood.
Your blood is a mix of a bunch of stuff pumped through tubes. Surrounding the tubes there’s other different stuff. Some of the stuff in your blood called platelets makes lumps when it touches the stuff called collagen just outside the tube. So if you make a hole in the tube, inside stuff and outside stuff makes lumps until the hole is blocked.
It pretty much clots when it touches anything besides these two things:
1) Other blood
2) Endothelial cells, which are special cells that line the inside of your blood vessels.
Touching basically anything else, including any other cells in your body, will kick off the clotting cascade. Blood really really likes to clot.
Whenever there is damage to the blood vessels, either vein or artery, a substance called tissue factor is released. That triggers platelets to start clotting.
Believe it or not, everyone has microscopic injuries to blood vessels everyday. The body forms small clots around the injuries and start to heal the vessels.
When blood exits the body, it will coagulate. Adding salt will keep it in liquid form. It’s not exactly an ELI5, but I learned this from butchering pigs. When I want to keep the pig blood in liquid form, I just add salt to it. If I don’t add salt to it, the blood I collect just becomes a solid clump. Later on, when I dilute the salty blood with water and bring the salt concentration down, the blood will coagulate and clump up.
There are 2 clotting pathways, the intrinsic and extrinsic pathways that eventually converge. But the short simple version is this: when there is tissue damage, it releases a chemical signal to recruit platelets and other clotting factors to area where they can eventually form a clot. Your blood in your body is in a constant state of both trying to clot and prevent clots from forming. Things liked deep vein thrombosis and blocked coronaries are examples of that balance going wrong, and things like scabs forming over a wound or microvasculature repair are examples of it going right.
If you want more detail try googling intrinsic clotting cascade, extrinsic clotting cascade and cell based model clotting cascade. There’s a lot that goes into it but there are some simple models/pictures of what’s going on
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