Answer :
Answer:
[circulatory system]
Explanation:
organs
[heart]
[veins]
[artery]
[aorta]
[lung]
[blood vessels]
veins
[the veins consist of three layers]
inner layer-
[comprised of endothelium and subendothelial and is lined with endothelial cells called the tunica intima]
middle layer-
[lined with smooth muscle called tunica media]
outer layer-
[lined with connective tissue called tunica externa or tunica adventitia]
[the inner layerof the vein is in direct contact with endothelial cells]
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