The Role Of Angiogenesis In Life And Diseases

Angiogenesis is the natural process of growing new blood vessels, a process that occurs in all higher forms of animals especially the mammals. This process plays a crucial role in the development of an embryo into a fetus and repairing of wounds. But when this process goes wrong the development of diseases such as tumors and cancer can occur. Fortunately, researchers have found a treatment to stop some cancer and tumor growth by reversing this process to stop the growth of blood vessels in areas around cancer cells and tumors thus killing the abnormal cells.

William Harvey discovered blood vessels in 1628 when he realized that the heart pump blood through the body in arteries and the blood return to the heart through veins. He performed a simple experiment by placing his fingers at two points on a vein and noticed that vein disappear between the two points. About 30 years later in 1161, Marcello Malphighi discovered the smallest vessels called capillaries that closed the circulatory system loop by connecting arteries to veins and around the same time Caspar Aselius discovered another vessel called lymphatic vessels. The purpose of the lymphatic vessels is to return blood plasma back to the blood circulatory system since blood plasma continuously leaks from the capillaries. This leakage occurs because blood is pushed through the circulatory system under pressure and the capillaries are porous.

Although the circulatory system developed early during evolution because the organs in higher organisms grew further apart as the organisms became more complex, the lymphatic system is only present in amphibians and animals further up the tree of life. Animals below amphibians such as fishes for instance do not have a lymphatic system.

Angiogenesis is a very important process in life especially during the embryonic development stage. This is the process that creates the first vessels of life in the embryo. The moment the heart starts beating in the embryo the process of angiogenesis is already generating blood vessels to the developing organs as the embryo develops into a fetus. Also during this time the blood vessels are sending signals to promote formation of the major organs in the body. For example, before the lungs can form the blood vessels will form first a lung shape network of vessels before the specialized tissues for the lungs form around them. This process is called organ morphogenesis.

Another very interesting event that occurs at this time is a process called vasculogenesis, the formation of small capillaries, where the fate of cells that make up these vessels have already been determined to function as arterial or venous vessels. This is an indication that the fate of these cells are genetically pre-programmed and are not determined by the direction of the blood flowing (hemodynamic force) through them.

As we grow into adults the process of angiogenesis stops generating new blood vessels in the body. But angiogenesis continues to occur in cycling ovary and during pregnancy when the placenta is growing for the developing fetus. Also when the body is subjected to a stressful physiological situation such as hypoxia, lack of or insufficient oxygen, for prolong period angiogenesis will produce more blood vessels in the lungs to increase the uptake of oxygen in the lungs. This generally occurs in people who live at high altitude in the Himalayans Mountains.

 Angiogenesis is reactivated during wound repair and during inflammation. But in many diseases the stimulus that turn on angiogenesis sometimes overwhelms the inhibitors that turn it off thus causing an excessive growth of blood vessels. Some of the disorders that develop when this happens are obesity, asthma, diabetes, cirrhosis, multiple sclerosis, endometriosis, AIDS, bacterial infections and some autoimmune diseases.

 There are diseases that occur when the inhibitors overwhelm the stimulus to produce blood vessels thus producing insufficient amount of blood vessels for the organ to function properly. Disorders such as respiratory distress (difficulty breathing) or cardiac failure are caused by insufficient blood vessel growth in these organs. Angiogenesis is also responsible for where the nerves grow in the body since they travel along the blood vessels to the various points in the body so these same organs have nerve transmission problem because a nerve or some nerves are missing for the organ to function properly. Irregular heat beats is a good example of transmission problem in the heart muscles due to improper placement of nerves.

Scientists are able to turn the process of angiogenesis on or off since they have discovered most of the chemical triggers that control this process.  For instance, there is a group of chemicals that promote the growth of tumors called necrosis growth factors. Scientists have produced anti-angiogenic drugs that stop the growth of blood vessels to tumors thus depriving the tumor of life sustaining blood and the tumor eventually dies. Since cancer cells require a lot of blood vessels just like tumors to survive, these same drugs have been used in the same way in the treatment of cancers along with other chemotherapy treatments. But keep in mind this treatment does not work on all forms of cancers. It does work well for patients with colorectal, breast or lung cancers when combined with chemotherapy treatments.

Angiogenesis or the administration of anti-angiogenic drugs to patients sounds like a promising treatment for cancer and other disorders caused by the malfunctioning of the process of angiogenesis. However, scientists must overcome another hurdle before this becomes a mainstream treatment for cancer and some of the other disorders mentioned. Some of these disorders are beginning to develop resistance to some of these anti-angiogenic drugs currently in clinical studies. Finally, scientists have to develop anti-angiogenic drugs that will only affect the blood vessels in the disease area and leave the normal vessels alone.

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