Exceptions to the rule

Exceptions to the rule - Exceptions to the rule 1 Portal...

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Unformatted text preview: Exceptions to the rule 1. Portal circulations These differ from those already described in having two capillary beds. The largest portal system covers the spleen, pancreas, stomach, small intestine. 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. 2. Anastomoses Arteries do not always end up as capillaries. They often anastomose with other arteries, either of equal (in the brain) or unequal size (elsewhere). In limbs anastomoses are most common around joints: quite clearly they form an alternative route when the main road is obstructed by, say, flexion of the elbow: they will also allow equalisation of pressure. 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 as you get further from the heart i....
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