Vascularisation

Vascularisation is the physiological process through which blood vessels form in tissues or organs. Vascularisation is crucial to supply the organs and tissues with an adequate supply of oxygen and nutrients and for removing waste products.

Blood vessels transport blood, water, and nutrients needed to support body systems. When blood vessels lose efficiency, it may lead to serious diseases such as cancer, heart disease, and diabetes. Scientists are currently working on ways to grow new blood vessels to help with tissue engineering and healing injuries.^{[citation needed]} This is why vascularisation is important in medicine.^[1]

Mechanisms

These are processes in which vascularisation happens and should not be confused with vascularisation itself:

Angiogenesis

Main article: Angiogenesis

It is the process where new blood vessels form from pre-existing ones. This happens naturally when the body needs to repair tissue or when a wound needs to heal. It is driven by signals from growth factors, such as Vascular Endothelial Growth Factor (VEGF), which prompts the formation of new vessels. However, this process can occasionally go wrong in tumour formation where it allows the tumours to create their own blood supply and grow larger, which can contribute to diseases like cancer.^[2]

Vasculogenesis

Main article: Vasculogenesis

This is the creation of blood vessels during early development particularly in embryos. Blood vessels start to form from special cells known as endothelial progenitor cells. While this process mostly happens during embryonic development, it can also occur in adults when the body needs to repair damaged blood vessels or grow new ones after an injury occurs.^[3]

Arteriogenesis

Main article: Arteriogenesis

This is a process where smaller and less efficient blood vessels become enlarged into fully functioning arteries. This usually happens in response to increased demand in the body such as during exercise or when blood vessels are blocked. This aids in ensuring that tissues are supplied with enough blood and oxygen.^[4]

Lymphangiogenesis

Main article: Lymphangiogenesis

This process is similar to angiogenesis but involves the creation of lymphatic vessels which are essential for draining excess fluid and fighting infections. This process is also key to conditions like inflammation and the spreading of cancer.^[5]

Applications in medicine

Cancer

In cancer, tumours take over the body’s vascularisation processes to supply themselves with blood, helping them grow and spread. Scientists are now developing therapies that block angiogenesis, cutting off the tumour blood supply.^[6][7][8][9] This has become a strategy in cancer treatments, with medications like bevacizumab that are being used to shrink tumours by preventing blood vessel growth.^[10]

Cardiovascular diseases

• In atherosclerosis, new blood vessels form within plaques, contributing to their growth and instability.^[11] These vessels are often fragile, allowing inflammatory cells and fats to enter, which can cause bleeding inside the plaque and increase the risk of rupture.^[12] Some studies in animal models suggest that blocking this vessel growth can reduce atherosclerotic progression.^[11]
• In a myocardial infarction, blocked blood flow deprives heart tissue of oxygen, leading to cell damage. Neovascularization in the surrounding area can help restore oxygen supply and limit further injury.^[13] Therapeutic angiogenesis, which encourages new blood vessel growth, is being explored as a potential treatment. Growth factors such as basic fibroblast growth factor (bFGF) and brain natriuretic peptide (BNP) have shown promise in promoting this process after a heart attack.^[14]
• Following a stroke, post-stroke angiogenesis occurs in the ischemic penumbra (the region surrounding the infarct core) which disrupts cerebral blood flow. This process helps restore perfusion and supports neurological recovery. Additionally, arteriogenesis, the enlargement of pre-existing collateral vessels, contributes to post-stroke blood flow restoration. Various immune cells and cytokines play a role in regulating angiogenesis after ischemic injury.^[15][16][17]

Wound healing

Vascularization is crucial for wound healing, as it provides oxygen and nutrients necessary for tissue repair.^[18] Angiogenesis temporarily increases vascular density around the wound, aiding the healing process.^[19]

Vascular endothelial growth factor (VEGF) is a key pro-angiogenic factor in this process, stimulating both vasculogenesis and angiogenesis in the skin.^[19] Impaired angiogenesis can result in delayed wound healing, as seen in conditions such as diabetes, where chronic wounds often exhibit reduced levels of active VEGF. Scientists are exploring ways to stimulate angiogenesis to help speed up healing, especially in persistent wounds.^[20][21][22]

Diabetic retinopathy

Main article: Diabetic retinopathy

Diabetic retinopathy is a complication of diabetes in which there is abnormal proliferation of microvessels in the retina, which can lead to vision loss^[23]