1. Serve as a physical lining of heart and blood vessels.
2. Secrete paracrine agents that act on adjacent vascular smooth muscle; these include the vasodilators prostacyclin and endothelium-derived relaxing factor (EDRF), and the vasoconstrictor endothelin-1.
3. Mediate angiogenesis (new capillary growth). Play a central role in vascular remodeling by detecting signals and releasing paracrine agents that act on adjacent cells in the blood vessel wall.
4. Serve as a permeability barrier for the exchange of nutrients, metabolic end-products, and bluid between plasma and interstitial fluid; regulate transport of macromolecules and other substances between plasma and interstitial fluid.
5. Undergo contractile activity, which regulates capillary permeability.
6. Influence vascular smooth-muscle proliferation in the disease atherosclerosis.
7. Secrete substances that regulate platelet clumping, clotting, and anticlotting.
8. Synthesize active hormones from inactive precursors.
9. Extract or degrade hormones and other mediators.
10. Function similarly to macrophages during immune responses.
11. Produce growth factors in response to damage.
12. Secrete cytokines during immune response.
13. Contribute to the formation and maintenance of extracellular matrix.