Difference between Arteri es & veins ?
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Answer:
Capillaries are tiny, extremely thin-walled vessels that act as a bridge between arteries (which carry blood away from the heart) and veins (which carry blood back to the heart).
The walls of veins and arteries are both made up of three layers:
Outer. Tunica adventitia (tunica externa) is the outer layer of a blood vessel, including arteries and veins. It’s mostly composed of collagen and elastic fibers. These fibers enable the veins and arteries to stretch a limited amount. They stretch enough to be flexible while maintaining stability under the pressure of blood flow.
Middle. The middle layer of the walls of arteries and veins is called the tunica media. It’s made of smooth muscle and elastic fibers. This layer is thicker in arteries and thinner in veins.
Inner. The inner layer of the blood vessel wall is called tunica intima. This layer is made of elastic fiber and collagen. Its consistency varies based on the type of blood vessel.
Unlike arteries, veins contain valves. Veins need valves to keep the blood flowing toward the heart. Theses valves are particularly important in the legs and arms. They fight gravity to prevent the backflow of blood. Arteries don’t need valves because the pressure from the heart keeps the blood flowing through them in one direction.