Arteries are muscular blood vessels that carry oxygenated blood away from the heart to the rest of the body. When a major artery is severely damaged or completely blocked, the vessel itself does not regenerate or “grow back.” The complex, multi-layered structure of a large artery cannot be reformed from scratch by the body’s natural processes. Instead of full regeneration, the body relies on two strategies: localized repair of minor damage and the creation of alternative blood supply routes. This combination of internal repair and natural bypass systems allows the circulatory system to maintain function despite injury or disease.
Repairing Existing Arterial Walls
The immediate response to minor wear and tear focuses on the innermost layer of the artery, known as the endothelium. This single-cell lining acts as a smooth surface that prevents blood clots from forming inside the vessel. When high blood pressure or disease causes small abrasions or micro-wounds in this lining, the body initiates a rapid repair sequence.
Nearby endothelial cells or specialized precursor cells, called endothelial progenitor cells, are activated to proliferate and migrate to the injury site. These cells fill the gap, effectively resurfacing the damaged area to restore the artery’s integrity. This localized cellular replacement maintains the existing structure of the artery and is highly effective for routine, microscopic damage.
However, the body’s self-repair capacity is limited to this surface-level restoration and cannot address major structural failure. Damage that extends deep into the muscular or connective tissue layers, such as a severe tear or long-term damage from atherosclerosis, requires medical intervention. The repair mechanisms are designed for maintenance, not for rebuilding a large section of a vessel that has burst or been surgically removed.
Forming New Blood Vessels to Compensate
When a major artery is blocked, the body’s primary long-term solution is to grow new pathways around the obstruction, a process known as collateral circulation. This involves two distinct methods of new blood vessel formation: angiogenesis and arteriogenesis. Angiogenesis is the creation of new, tiny capillaries that sprout from existing vessels in response to low oxygen levels in the surrounding tissue. This process is triggered by ischemia, which signals the need for more oxygen delivery.
The more significant natural bypass system is arteriogenesis, which is driven by mechanical forces rather than low oxygen. When a main artery is blocked, the blood pressure gradient shifts, causing increased flow velocity and fluid shear stress in the small, pre-existing side channels. This increased shear stress activates the endothelial cells in these tiny collateral arterioles.
The activated cells release growth factors and recruit immune cells, leading to the remodeling of the vessel wall. Over time, these small arterioles widen and mature, developing thicker, muscular walls to handle the increased blood flow. This transformation effectively creates a new, functional artery that bypasses the original blockage, restoring blood supply. While the collateral circulation may not achieve the full capacity of the original artery, it often provides enough blood flow to preserve tissue function.
Surgical Options for Arterial Replacement
Since the body cannot regenerate a large, complex artery, medical science has developed procedures to replace or bypass severely damaged segments. The most common solution for severe blockages, such as in the heart, is Coronary Artery Bypass Grafting (CABG). This surgery reroutes blood flow around the blocked section of the coronary artery by connecting a healthy vessel from a different part of the body.
These replacement vessels, called grafts, are typically harvested from the patient, making them autologous grafts. Common choices include the internal mammary artery from the chest or a segment of the saphenous vein from the leg. Surgeons sew one end of the graft onto the aorta and the other end onto the coronary artery beyond the blockage, creating a functional bypass.
For larger arteries or when a patient’s own vessels are unsuitable, synthetic grafts made of materials like PTFE or Dacron are used to replace or bridge the gap. Another common intervention involves the use of stents, which are mechanical supports rather than replacements. During angioplasty, a tiny metal mesh tube is expanded inside a narrowed artery to push the plaque against the wall and prop the vessel open. Some stents are coated with anti-proliferative drugs, known as drug-eluting stents, which help prevent the artery from narrowing again. Endovascular stent-grafts are also used for conditions like aneurysms to reinforce a weakened arterial wall and prevent rupture.