Blood supplying these, having passed through their capillary network ends up in the hepatic portal vein, which drains into the liver and through a hepatic capillary bed, where products of digestion are removed, processed and stored. A second, smaller but equally important portal system is found connecting the brain and pituitary gland. Anastomoses Arteries do not always end up as capillaries. They become more frequent as you get further from the heart i.e. as the arteries get smaller, so that arterioles tend to form a network. If you cut an artery which forms part of an anastomosis it will bleed from both ends.
Anastomoses form the basis of collateral circulation.
This is seen in the head of the femur, scaphoid after fracture and central artery of the retina, and in coronary arteries supplying heart muscle - end arteries. These are important shortcuts from artery to vein cutting out capillary bed. These are seen as a. preferential thoroughfares - areas of a capillary bed are deferentially supplied with blood under different demands. Areas are then restricted by closing precapillary sphincters. Absent in newborn, atrophy in old age - so wrap up newborns and grannies.