Wednesday, October 7, 2009
angiogenesis-8th unit-btechbiotechnology-2-1 syllabus
Angiogenesis is a physiological process involving the growth of new blood vessels from pre-existing vessels. Though there has been some debate over this, vasculogenesis is the term used for spontaneous blood-vessel formation, and intussusception is the term for new blood vessel formation by splitting off existing ones.]
Vasculogenesis – Formation of vascular structures from circulating or tissue-resident endothelial stem cells (angioblasts), which proliferate into de novo endothelial cells. This form particularly relates to the embryonal development of the vascular system.
Angiogenesis – Formation of thin-walled endothelium-lined structures with/without muscular smooth muscle wall and pericytes (fibrocytes). This form plays an important role during the adult life span, also as "repair mechanism" of damaged tissues.
Arteriogenesis – Formation of medium-sized blood vessels possessing tunica media plus adventitia.
Because it turned out that even this differentiation is not a sharp one, today quite often the term “Angiogenesis” is used summarizing all different types and modifications of arterial vessel growth
Metastasis Requires Angiogenesis
Cancer researchers studying the conditions necessary for cancer metastasis have discovered that one of the critical events required is the growth of a new network of blood vessels. This process of forming new blood vessels is called angiogenesis.
Tumor angiogenesis is the proliferation of a network of blood vessels that penetrates into cancerous growths, supplying nutrients and oxygen and removing waste products. Tumor angiogenesis actually starts with cancerous tumor cells releasing molecules that send signals to surrounding normal host tissue. This signaling activates certain genes in the host tissue that, in turn, make proteins to encourage growth of new blood vessels.
cancer researchers believed that the blood supply reached tumors simply because pre-existing blood vessels dilated. But later experiments showed that angiogenesis--the growth of the new blood vessels--is necessary for cancerous tumors to keep growing and spreading.
What Prompts Angiogenesis?
In an experiment designed to find out whether molecules from the cancer cells or from the surrounding host tissues are responsible for starting angiogenesis, scientists implanted cancer cells in a chamber bounded by a membrane with pores too small for the cells to exit. Under these conditions, angiogenesis still began in the region surrounding the implant. Small activator molecules produced by the cancer cells must have passed out of the chamber and signaled angiogenesis in the surrounding tissue.
Among these molecules, two proteins appear to be the most important for sustaining tumor growth: vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF). VEGF and bFGF are produced by many kinds of cancer cells and by certain types of normal cells, too
Without Angiogenesis, Tumor Growth Stops previousnext
In early experiments, researchers asked whether cancer growth requires angiogenesis. Scientists removed a cancerous tumor from a laboratory animal and injected some of the cancer cells into a normal organ removed from the same strain of animal. The organ was then placed in a glass chamber and a nutrient solution was pumped into the organ to keep it alive for a week or two. Scientists found that the cancer cells grew into tiny tumors but failed to link up to the organ's blood vessels. As a result, tumor growth stopped at a diameter of about 1-2mm. Without angiogenesis, tumor growth stopped.