Hello :)
Why at the beginning at least tumors grow without vasculature ? When healthy tissues grow, the vasculature grows as well, so why are tumour cells different from healthy tissues ?
Thank you in advance
Hello Joseph Ackermann
The outgrowth of the carcinogenic cells releases the Vascular endothelial growth factor (VEGF) under hypoxic conditions, that promotes vasculature inside the cancerous tissue.
VEGF is essential for the directive vasculature inside the tissue.
Hello Joseph Ackermann
As tumor gets bigger, the central part of the tumor gets further and further away from the blood vessels in the area where it is growing. So, the central part of the tumor gets less oxygen and nutrient supply. Like healthy cells, the cancer cells also require oxygen and nutrients for survival. So, to survive they send out signals termed as angiogenic factors like vascular endothelial growth factor (VEGF) produced by tumor cells in the primary tumor microenvironment, which bind to endothelial cell receptors like VEGFR2 and initiate the sequence of angiogenesis.
When the endothelial cells are stimulated to grow, they secrete proteases, heparanase, and other digestive enzymes that digest the basement membrane surrounding the vessel. Thus, these factors encourage new blood vessels to grow into the tumor. Once a cancer can stimulate blood vessel growth it can grow bigger, and then it can stimulate the growth of hundreds of new small blood vessels (capillaries) to bring in nutrients and oxygen. Without blood supply, the tumor cannot grow much bigger than a pin head.
Hope this helps.
Best.
Hello Dinesh Raj Pant and Malcolm Nobre thank you for your answers !
But I was wondering whether for healthy tissues also angiogenesis was triggered by hypoxia. I mean when an organ grows (let's say somebody is getting fatter, or a kid is growing, even though I don't know if those are good examples), do tissues grow, and then become hypoxic, and then produce blood vessels or is there a mechanism that triggers angiogenesis without getting through hypoxia ?
Hello Joseph Ackermann
I don't know much much angiogenesis mechanism in healthy tissue. Although I infer that under normal physiological conditions, the tissue growth is well coordinated by the influence of growth hormone or other factors that influence growth of particular tissue. Probably thereby, both tissue and vascular growth get synchronized and hypoxic condition may not appear.
This is all I can infer, however other reason may get involved in it.
I think it's a good question. Actually, I can't answer this well. I will share my opinion with you.
First, angiogensis is quiescent in phsiological condition in adults and emergency like tissue damage would start angiogensis However, angiogenesis with the development of human body is related to blood vessel branching and elongation. It's a complex question. Besides,the oxygen level and nutrient supply is different among different tissue microenvironment. For example, the oxygen content of lung is 3~5 times to central nervous system. Thus, the angiogenesis pattern，trigger and stopper, maybe different among tissues.