Tissue arrangement in the internal elastic lamina of the rat muscular pulmonary artery.

The arrangement of tissue in the internal elastic lamina of muscular pulmonary arteries in rats has been studied. It consists of long plates of elastic tissue joined to each other by side branches, thus forming a continuous branching network. The thick plates are orientated parallel to the long axis of the vessel. This is similar to the arrangement in the saphenous and splenic veins in the dog. Systemic arteries show a different arrangement, usually a single fenestrated sheet. The differences between systemic and pulmonary arteries can be explained by considering the different biomechanical forces acting on them.