Final answer:
Platelets do not adhere to healthy blood vessels due to a coating of prostacyclin, which prevents thrombosis by inhibiting platelet aggregation and promoting vasodilation.
Step-by-step explanation:
In healthy blood vessels, platelets do not adhere to the endothelium because it is coated with prostacyclin. Prostacyclin is a potent vasodilator and inhibitor of platelet aggregation, which helps to maintain a smooth, non-thrombogenic endothelial surface. If platelets were to adhere to normal vessel walls, it could lead to thrombosis, an undesirable clot formation within a blood vessel. The production of prostacyclin by the endothelial cells is a critical mechanism in preventing clot formation under normal conditions.
Plasma anticoagulants like antithrombin and heparin play a role in limiting coagulation to the region of injury and restoring a normal, clot-free condition of blood. They ensure that clotting does not extend beyond the site of injury, which is essential for preventing excessive thrombus formation that could impair blood circulation.