Blood Vessel Growth: How It Helps and Harms the Body
Understand the dual nature of blood vessel formation, a critical biological process that supports life and repair but can also fuel disease.
The creation of new blood vessels is a biological process that allows the body to grow, repair itself, and adapt to changing demands. This expansion of the circulatory system ensures that tissues and organs receive the oxygen and nutrients needed to function. The process is tightly regulated, occurring at specific times and locations to support the body’s needs throughout life.
The Mechanisms of Vessel Formation
The body forms blood vessels through two primary methods: vasculogenesis and angiogenesis. Vasculogenesis is the formation of the first vascular network, occurring during embryonic development. In this process, precursor cells called angioblasts differentiate into endothelial cells, which line all blood vessels, and assemble into new arteries and veins from scratch.
Following this initial phase, the vascular network expands through angiogenesis, the sprouting of new vessels from pre-existing ones. This process is responsible for most blood vessel growth after the embryonic stage. Angiogenesis begins when endothelial cells in an existing vessel receive chemical signals that prompt them to break down the surrounding tissue, migrate, and multiply to form a new vessel sprout.
A signaling molecule orchestrating this process is the Vascular Endothelial Growth Factor (VEGF). When tissues require more oxygen, they release VEGF, which acts as a chemical attractant. This protein binds to receptors on nearby endothelial cells, stimulating them to differentiate into specialized “tip” cells that guide the new sprout and “stalk” cells that proliferate to elongate the new vessel.
The endothelial cells must first degrade the basement membrane, a thin layer surrounding the vessel. The migrating cells then organize into a tube, which develops a central opening, or lumen, to allow blood flow. This controlled formation ensures new vessels are created only where needed.
Beneficial Roles in the Body
Blood vessel formation is necessary for growth and development, beginning in the embryo. Vasculogenesis establishes the first arteries and veins, a framework later expanded by angiogenesis to support growing organs. This ensures the developing fetus receives oxygen and nutrients from the placenta.
In adults, angiogenesis is part of tissue repair and maintenance. When an injury occurs, the growth of new blood vessels into the damaged area is a step in healing. These new capillaries deliver oxygen, nutrients, and immune cells to clear debris and rebuild tissue, allowing wounds to heal.
The body also uses angiogenesis to adapt to physiological demands like physical exercise. Endurance training prompts the growth of new capillaries within muscles, increasing their oxygen capacity and improving performance. A similar process occurs during the female reproductive cycle, as the uterine lining develops new blood vessels each month in preparation for pregnancy.
Connection to Disease Development
The same mechanisms that support life can contribute to disease when dysregulated, a process known as tumor angiogenesis in cancer. Solid tumors require a dedicated blood supply to grow beyond a small size. To achieve this, cancer cells release large quantities of signaling molecules like VEGF, hijacking the body’s vessel-forming machinery.
These new tumor blood vessels are often abnormal and leaky, which facilitates metastasis. Cancer cells can enter these poorly formed vessels and travel through the bloodstream to establish new tumors in distant parts of the body. A tumor’s ability to induce angiogenesis is a characteristic of its transition from a benign to a malignant state.
Beyond cancer, abnormal blood vessel growth is a feature of certain eye diseases. In wet age-related macular degeneration, uncontrolled angiogenesis occurs beneath the retina, where new, fragile vessels leak blood and fluid, damaging light-sensitive cells and causing vision loss. In diabetic retinopathy, high blood sugar damages retinal vessels and triggers the growth of new, unstable ones that can bleed and cause scarring.
Therapeutic Control of Blood Vessel Growth
Medical science has developed strategies to manipulate blood vessel formation for therapeutic benefit. These interventions are categorized into two opposing approaches: those that inhibit vessel growth and those that stimulate it.
Anti-angiogenic therapies are designed to block the growth of new blood vessels and are used in oncology to starve tumors of their blood supply. Drugs like bevacizumab work by neutralizing VEGF, the signaling molecule tumors use to recruit new vessels. Similar anti-VEGF agents are injected into the eye to treat conditions like wet age-related macular degeneration, preventing the vessel growth that damages vision.
Conversely, pro-angiogenic therapies aim to stimulate new blood vessel formation where needed. This approach may treat conditions caused by insufficient blood flow, like coronary and peripheral artery disease. The goal is to encourage new collateral vessels to bypass blocked arteries, restoring circulation. While often experimental, these therapies may involve delivering growth factors like VEGF to the affected area.