Atlant’s Column: Contact Adhesive in the Blood

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Welcome to the section on Micronaut.ch which explores, analyzes and explains fascinating microscopical structures.

The human body is basically a fluid-filled cavity. Thus its greatest enemies are sharp objects and knives. If they bore into the fine network of blood vessels under the skin, we literally run out. But not for long. Just ten seconds after an injury, an automatic process starts that seals the hole within a few minutes. We all know it as “blood clotting”.

Text by science writer Atlant Bieri
Photography by Martin Oeggerli

 The image shown at right shows the leak two minutes after a sharp object bore into the vessel. Coagulated blood has already formed a solid plug and closed the wound. It all started with the pink lump (see round section below). This is a thrombocyte. These cells belong to the most dangerous of our body, because in case of malfunction, they could turn our entire blood immediately into gelatine, which would mean certain death.

Nevertheless Mother Nature has furnished our body quite lavishly with them. Each person is equipped with up to 380’000 thrombocytes per micro litre of blood. But there is a reason that we carry this explosive charge around with us: It saves our life every single day. These cells are the equivalent of a contact adhesive that is activated as soon as the smallest vascular injury occurs and thus prevents us from bleeding to death because of a pinprick.

 

The Thrombocyte-Collagen Relationship

The substance that makes thrombocytes freeze is called collagen. It is the most abundant protein in our body and occurs almost everywhere. Even blood vessels are made of it, except the inner lining of the vessels and the blood itself are collagen-free area. This means that thrombocytes remain dissolved as long as nothing breaks.

This all changes abruptly in case of an injury. Thrombocytes flow out through the wound opening where they meet a lot of collagen. On its surface there are specific docking sites, where the thrombocytes can bind to and thus solidify into a plug. This plug, however, is not very stable and in danger of being swept away by the shear forces of the blood stream. But the thrombocytes know how to help themselves: they start to puke. Doing this they flood the surrounding blood with a whole cocktail of different proteins.

Some of these substances give them a better grip. They reinforce the connection to the collagen and thus prevent the plug being washed away. Others cause the crystallisation of certain proteins in the vicinity of the wound. Seemingly out of nowhere long poles start to emerge. This is the so-called fibrin. The poles form a fishing net (here coloured purple) that wraps the gaping wound. In this dense network the larger red blood cells (orange slices) get stuck. The resulting collision of cells plugs up the leak until the bleeding completely stops.

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Continue reading Atlant’s Column: Sperm in Concrete, March 2012, or go back to the archive