During angiogenesis how do new capillaries form by branching out from existing ones while maintaining a closed circulatory system?

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During angiogenesis how do new capillaries form by branching out from existing ones while maintaining a closed circulatory system?

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The circulatory system is a closed loop from start to finish. Unless pathological, there shouldn’t be a free “open end”.

So, when a capillary needs to grow, it does so by producing more epithelial cells and they sort of make a pocket or outward pouch in one of these side of these capillaries and then when more epithelial cells grow this pocket extends to make a tube or branches into multiple tubes, but these tubes are still closed. There is a “tip cell” at the end of them that prevents blood leaking out and directs the blood vessel growth into areas with low oxygen.

You can sort of think of this as the original capillary being stretched out in that direction. Imagine if you get a really stretchy tube and you stick your finger inside it and try to poke through the wall from inside out. There is no gap or hole at your finger tip, but there is effectively a “new tube” surrounding your finger. This is kind of like what happens to capillaries in angiogenesis except nothing it being stretched, they’re just producing new capillary wall in that direction.

I don’t think I’ve explained it very well but if you google a diagram of angiogenesis, hopefully that in combination with my comment will make sense if my comment doesn’t do the job on it’s own. If not, I’m happy to try to clarify.