Final answer:
The two primary tissues found within a vein are the tunica intima and the tunica media, the inner and middle layers of the vessel, which are surrounded by the outermost tunica externa providing support and protection.
Step-by-step explanation:
Within a vein, two primary tissues can be identified, which are also referred to as tunics. These tunics are the tunica intima, the innermost layer composed of endothelium and a small amount of connective tissue, and the tunica media, which is the middle tunic composed of smooth muscle cells and elastic fibers. The tunica media is followed by the tunica externa, the outermost layer made up of connective tissue that supports and protects the blood vessel.
Unlike arteries, veins have a thinner tunica media and externa, as the blood pressure within veins is lower than in arteries. This structural difference is also complemented by the presence of valves in veins that help prevent backflow of blood, ensuring unidirectional flow towards the heart, especially from the lower limbs where blood must travel against gravity. The contraction of skeletal muscles further assists the movement of blood in veins back to the heart.