They are frequently associated with pregnancy and there may be hormonal factors associated with their development. They are primarily of cosmetic concern and do not present any medical concerns.
Varicose veins, swollen tortuous veins, are called varices in medical terms.
Yes, seek medical advise as this could indicate a clot forming.
Nothing - it's when your veins aren't blue that there's a problem.
Varicose Veins.
malfunctioning valves in veins
The answer to that is varicose veins.
Blood is not blue. That found in veins are slightly darker than those found in arteries (usually). You may have seen drawings in which the veins are blue but is just to indicate that these blue vessels are veins.
Venopathy; phlebopathy
varicocele
Blood vessels
It is a clot in the (phlebitis) inflammation of the superficial veins.
The veins and their tributaries are collectively called the venous system. The other part of the circulation is the arterial system.