Final answer:
C3a and C5a are critical components of the complement system that contribute to the inflammatory response by inducing vasodilation and increasing vascular permeability to attract immune cells to the site of infection.
Step-by-step explanation:
The purpose of C3a and C5a, the split-products of the complement cascade, is to induce vasodilation and increase vascular permeability. While C3b, a larger fragment, binds to the surface of the pathogen for opsonization (labeling for phagocytosis), C3a and C5a have other vital roles in the immune response. These smaller complement fragments act as chemotactic agents that attract phagocytic cells, like macrophages and neutrophils, to the site of inflammation and infection. Moreover, they contribute to the inflammatory response by causing vasodilation, which increases blood flow and leads to the redness and warmth associated with inflammation. This process also increases the permeability of blood vessels, allowing more immune cells to reach the affected area.