Final answer:
Collagen is the by-product that can replace defective human heart valves due to its strength and flexibility. It's also important for coagulation, and defects in collagen, like in Ehlers-Danlos syndrome, can affect blood clotting.
Step-by-step explanation:
The by-product that can be used to replace defective human heart valves is collagen. Heart valves can be replaced with biological prostheses, often made from pig heart valves, that are rich in collagen. Collagen provides the necessary combination of strength and flexibility to function similarly to natural heart valves.
Regarding the descriptions provided:
- Collagen is a protein that provides structural support in connective tissues, such as tendons and ligaments, and is integral to the structural integrity of heart valves.
- Elastin is a protein that allows tissues to resume their shape after stretching or contracting, contributing to the elasticity of the skin and blood vessels.
- Keratin is a protein found in hair, nails, and the outer layer of skin.
- Chondroitin is not a protein but a component of cartilage that helps it retains water and maintain tissue flexibility.
Desmosomes can be found in tissues like muscle cells and skin cells (option b), where they provide mechanical strength and flexibility. As for collagen's role in coagulation, defective collagen, such as that in Ehlers-Danlos syndrome, may affect platelet adhesion and clot formation since collagen is involved in the initial stages of blood clotting.