Vein Structure

The circulatory system of arteries, veins and capillaries -- the machinery of body's blood flow system -- is about 60,000 miles long. Veins are located extensively throughout the body.

Function

Veins primarily function to deliver deoxygenated blood from the body's tissues and organs to the heart. Veins are made up of three layers called tunica adventitia, tunica media and tunica intima.

Tunica Adventitia

The tunica adventitia is the outer layer of the vein consisting of connective tissues, collagen and elastic fibers. Proteins are worker molecules or substances that are necessary for virtually every activity in your body. Elastic fibers are made of proteins, and their elastic nature give veins flexibility, allowing them to withstand fluctuating pressure of venous blood. Collagen, also made of protein, adds additional structure and support to the vein.

Tunica Media

The tunica media is the middle layer of the vein that consists of smooth muscle and elastic fibers. Smooth muscle enables vein contraction, assisting blood flow throughout veins.

Tunica Intima

The tunica intima is the innermost layer and has direct contact with blood. It consists of smooth endothelial cells. Endothelial cells are layers of cells that typically line and protect body organs. Valves line this internal layer, preventing the backward flow of blood.

References

• Random Facts: 37 Interesting Facts About the Human Body
• Teach PE: Veins
• National Institute of General Medical Sciences: Proteins are the Body's Worker Molecules
• RCSB Protein Data Bank: Collagen