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.
Most connective tissues are vascularized (except cartilage). The extracellular spaces (space outside of cells) in connective tissue are referred to as the extracellular matrix. Connective tissue, therefore, is made up of cells and extracellular matrix. The extracellular matrix is composed of glycosaminoglycans and proteoglycans. It is variations in the composition of the extracellular matrix that determine properties of the connective tissue. Connective tissue is made up of: Fibrous components (collagen and elastin)