Osmosis video - Artery and vein histology

Arteries are blood vessels that carry oxygen-rich blood from the heart to the body tissues, whereas veins are blood vessels that carry oxygen-poor blood from the body tissues back to the heart. The walls of both the arteries and veins are made up of three layers: the tunica intima, the tunica media, and the tunica adventitia.

The tunica intima is the innermost layer and is made up of a thin layer of endothelial cells that line vessels' lumen. The tunica media is the middle layer and is composed of smooth muscle cells and connective tissue. The tunica adventitia is the outermost layer and consists of connective tissue that anchors the vessel to surrounding tissues. Arteries typically have a thicker tunica media and a narrow lumen, compared to veins which have thinner tunica media, and a wide lumen.