Red blood cells (RBCs), also known as erythrocytes, deliver oxygen to the tissues in your body. Due to hemoglobin, blood is red.
Veins carry blood toward the heart. Veins carry deoxygenated blood toward your heart and are often located close to your skin.
Veins don’t have a muscular layer like arteries do, so they rely on valves to keep our blood moving to prevent a backflow of blood.
This outermost layer is composed of connective tissue with varying amounts of elastic and collagenous fibers to provide structural support and shape to the vessel.
The tunica media consists of smooth muscle cells intermingled with elastic fibers. It supports and helps regulate the internal vessel diameter to help blood flow and pressure. This layer is much thicker in arteries than in veins.
It comprises a single layer of endothelial cells and connective tissue that serves as a frictionless contact surface for blood flow. This layer has many valves to prevent the backflow of blood.