In anatomy or zoology, lacking valves; having no valve structures, especially referring to blood vessels or other anatomical features.
From the prefix 'a-' (without) plus 'valvular' (having valves, from Latin 'valva,' a folding door). The term is primarily used in medical and anatomical contexts.
In most animals, capillaries are avalvular—they lack the one-way valves found in veins and arteries, which is why blood can only flow in one direction through them due to pressure differences, not mechanical gates.
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