Glossary / Life sciences and medicine
Blood clotting
The mechanism by which blood solidifies to seal a damaged vessel. A clot that forms inside a blood vessel is called a thrombus.
Blood carries more than a dozen clotting factors in an inactive form. In 1964 Earl Davie and Oscar Ratnoff described how a single trigger sets one factor activating the next in sequence, amplifying the reaction like a waterfall[1]. At the end, fibres of a protein called fibrin form and set the blood.
The system does not mesh well across species. When a pig organ is placed in a person, the lining of the pig's vessels fails to restrain human clotting properly, and small clots tend to form in the organ's fine vessels. Pigs bred for xenotransplantation are therefore given human genes that hold clotting in check.
Related terms
- XenotransplantationTransplanting organs or tissues from animals into humans. Today the main candidates are kidneys and hearts from genetically modified pigs.
- Antibody-mediated rejectionRejection in which the recipient produces antibodies against a transplanted organ, and those antibodies attack the organ's blood vessels and gradually impair it.
- Genetic modificationDeliberately rewriting the genes of a living thing: switching particular genes off, or adding genes from another species.