An agent that is smaller than a virus causes scrapie. It is either a protein called a prion or it is another substance closely associated with the prion protein. Scientists still have a lot to learn about the scrapie agent and exactly how it works.
Tissue valves are made with tissues from porcine (pig) heart valves or bovine (cow) cardiac tissue because they function like human heart valves. Once the tissue is removed from the animal, it is chemically treated to preserve the tissue and prevent immulogic reactions once it is placed in a patient.
see cardiac valve laceration (above). cardiac valves. heart valves formed by evaginations of the cardiac and vascular endothelium supported by connective tissue; includes atrioventricular and semilunar valves on both sides of the heart.cardiac valvular disease. see valvular disease.ee cardiac valve laceration (above). cardiac valves. heart valves formed by evaginations of the cardiac and vascular endothelium supported by connective tissue; includes atrioventricular and semilunar valves on both sides of the heart. cardiac valvular disease. see valvular disease.