Understanding ANASTOMOSIS and COLLATERAL CIRCULATION

CIRCULATORY ANASTOMOSIS

Arteries do not always end in capillarie; in many cases they unite with one another, forming what are called anastomosis

Anastomoses occur normally in the body in the circulatory system, serving as backup routes for blood to flow if one link is blocked or otherwise compromised. There are many examples of these in the body. However clinically important examples include:
Circle of Willis (in the brain)
scapular anastomosis (for the subclavian vessels)
joint anastomoses - clinically very important. Almost all joints receive anastomotic blood supply from more than one source. Examples include knee (and geniculate arteries), shoulder (and circumflex humeral), hip (and circumflex iliac) and ankle.
pelvic anastomoses
abdominal anastomoses
hand and foot anastomoses (which include the palmar and plantar arches)
Coronary: anterior and posterior interventricular ries of the heart circle of Willis

Coronary anastomoses are a clinically vital subject:

The coronary anastomosis is the blood supply to the heart. The coronary arteries are vulnerable to arteriosclerosis and other effects. Inadequate supply to the heart will lead to chest pains (angina) or a heart attack (myocardial infarction).
Coronary anastomoses are anatomically present though functionally obsolete. There was some suggestion that they may be helpful if a problem develops slowly over time (this will need to be verified) but in the case of the pathogenesis of CHD(coronary heart disease) they do not provide a sufficient blood flow to prevent infarction.
There are anastomoses between the Circumflex and right coronary arteries and between the anterior and posterior inter-ventricular arteries. In the normal heart these anastomoses are non-functional.

Collateral Circulation

What is collateral circulation?
This is a process in which small (normally closed) arteries open up and connect two larger arteries or different parts of the same artery. They can serve as alternate routes of blood supply.
Everyone has collateral vessels, at least in microscopic form. These vessels normally aren't open. However, they grow and enlarge in some people with coronary heart disease or other blood vessel disease (such as in the case of stroke). While everyone has collateral vessels, they don't open in all people.

How does collateral circulation help people with heart disease?
When a collateral vessel on the heart enlarges, it lets blood flow from an open coronary artery to an adjacent one or further downstream on the same artery. In this way, collateral vessels grow and form a kind of "detour" around a blockage. This collateral circulation provides alternate routes of blood flow to the heart in cases when the heart isn't getting the blood supply it needed

How does collateral circulation help people with stroke?
When an artery in the brain is blocked due to stroke or transient ischemic attack (TIA), open collateral vessels can (but not always) allow blood to "detour" around the blockage. This collateral circulation restores blood flow to the affected part of the brain. However, not all people can develop “collateral circulation,” so prevention of heart disease and stroke should always be the gold standard.