Representative Normal Pulmonary Precapillary Vessels
Left: A large elastic pulmonary artery has intact elastic layers and intervening smooth muscle.
Middle: A muscular pulmonary artery of the acinus has a thin muscular media between inner and outer elastic laminas. There is little adventitia.
Right: An intra-acinar arteriole has a single elastic layer and no media. These vessels become muscularized in hypertensive states.
Elastic van Gieson stain
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