Bleeding, or hemorrhage, is the process of blood escaping from the circulatory system, typically through a wound or rupture in a blood vessel. The immediate biological response to blood loss is a complex cascade designed to limit further fluid escape and initiate clotting. When a vessel wall is breached, specialized platelets and clotting factors become activated, forming a mesh of fibrin and other proteins to create a stable clot. The rate of blood loss and the underlying vascular structure determine the severity of bleeding. Clinically, excessive or prolonged bleeding can lead to hypovolemic shock due to the resulting decrease in circulating blood volume and oxygen-carrying capacity.