Final answer:
When released by platelets, ADP helps additional platelets adhere to the injury site, reinforcing and expanding the platelet plug. Serotonin, released by platelets, maintains vasoconstriction.
Step-by-step explanation:
When released by platelets, ADP (adenosine diphosphate) serves to help additional platelets adhere to the injury site, reinforcing and expanding the platelet plug. This process is important for hemostasis, as the platelet plug helps prevent excessive bleeding. ADP plays a role in platelet activation and aggregation, leading to the formation of a stable plug at the site of injury.
To further enhance hemostasis, platelets also release serotonin, which maintains vasoconstriction. Vasoconstriction helps narrow the blood vessels, reducing blood flow to the injured area and aiding in the formation of a clot.