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I got curious what really happens to the cut blood vessels after they were operated on at an arbitrary point... and how the blood circulation remains consistent(, especially if the blood vessel is a significant one, - of course not artery, but - I wouldn't think capillaries really matter).

This question came up since I can't imagine that a vein, which was connected to capillaries earlier, could do its duty and transport CO2-rich blood back to the heart after it's cut any more... I'd kinda expect that it becomes a dead end.

How does a human organism solve this?

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What happens when a blood vessel is cut during surgery?

Blood vessels (not just veins, but arteries also) are transected (cut), ligated (tied off), and/or cauterized (burned closed) in just about every surgical procedure ever. When done appropriately, this does not cause a problem because there is more than one path from the heart to the tissue and more than one path from the tissue back to the heart. This is called collateral circulation and often involves vascular anastomoses. In some cases collaterals are quite abundant, for example, the rectal plexus, the vascular supply relevant to the title to your question. Hemorrhoids are, in fact, the result of a very particular kind of venous branching, a porto-systemic communication. The rectal and anal circulation are drained through two parallel pathways, the portal circulation (through the superior rectal vein) and the systemic circulation (through the middle and inferior rectal veins). The portal circulation returns blood from the gastrointestinal system to the liver (and from there to the inferior vena cava and the heart), where the systemic circulation returns blood directly to the inferior vena cava (without passing through the portal system of the liver). When the pressure in the portal system increases (whether through pathological portal hypertension, or other, temporary nonpathological conditions, e.g., pregnancy), blood is shunted from the portal arm through to the systemic arm, engorging the vessels in a few specific areas. The rectal plexus is one of them, and is a clear demonstration of the principle that there is more than one path back to the heart.

An important part of good surgical technique is identifying which blood vessels can be cut, tied, or burned, and which ones can't (or will result in complications if they are).

  • 1
    This is an outstanding answer. I really appreciate your ability to explain A&P in a succinct, understandable fashion. That's a real talent. – Carey Gregory Feb 14 '19 at 5:46
  • @CareyGregory Thanks! Your specific positive feedback is actually quite useful :) – De Novo Feb 14 '19 at 5:54
  • Just as a nice to know: This is why rectal suppositories are quite effective: They immediately enter the blood stream and bypass the liver via the V. cava inferior. – Narusan Feb 14 '19 at 10:25

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