What is the main function of veins?

Veins are responsible for returning deoxygenated blood from capillaries back to the heart. They act as capacitance vessels, meaning they can expand to accommodate varying blood volumes.

How do veins differ from arteries in structure?

Veins have thinner walls and larger lumens than arteries. Their thickest layer is the tunica adventitia (unlike arteries where the tunica media is thickest), and they contain valves to prevent backflow.

What are the three main types of veins?

Veins are classified into three main types: large veins (e.g., superior and inferior vena cava), medium-sized veins (e.g., splenic, renal veins), and small veins/venules (postcapillary and muscular venules).

What is the purpose of venous valves and where are they found?

Venous valves are semilunar folds that ensure unidirectional blood flow toward the heart. They are most numerous in limb veins but absent in veins like the superior vena cava, inferior vena cava, and portal vein.

What causes varicose veins?

Varicose veins result from chronic venous insufficiency due to valve failure. This leads to dilation and tortuosity of veins, commonly affecting the great saphenous vein.

How is blood flow in veins assisted?

Venous return is assisted by the skeletal muscle pump, valve action preventing backflow, and muscle loops near tributary entries acting as sluice gates.

Veins – Structure, Valves & Venous Return