Veins hold up to 70% of the entire blood and are very distensible. They can endure huge changes in volume, resulting from a haemorrhage or transfusion. Some veins can constrict in response to nerve stimulation.
Blood samples are normally taken from veins, having thinner walls, larger diameters and lower blood pressure compared to arteries. Larger veins possess one-way valves ensuring that blood travels in the correct direction and preventing the development of undue back pressure. Sometimes valves cease to function, causing veins to distend permanently, with blood flowing backwards and collecting in the vein. Swollen and enlarged veins are called varicose – usually blue or dark purple. In appearance, they may be twisted, lumpy or bulging. Varicose veins are usually due to weak vein walls and valves. In rare cases, causes may be: previous blood clot, swelling or tumour in the pelvis, abnormal blood vessels. Varicose veins’ symptoms include pains, dry skin and colour changes in the lower leg, heavy legs, swollen feet and ankles or muscle cramps. Varicose veins are a common condition, affecting up to 35% of adults. The first recorded case of varicose veins dates back in 86 BC, when the Roman general Caius Marius described his suffering. Giraffes have the greatest pressure in their legs amongst all animals. Yet, they never get varicose veins because of their extremely thick skin. Up to 75% of men are affected by varicocoele, which is a vein enlargement that occurs in the left testicle and cause discomfort. Any vein can become varicose, but as standing and walking put extra pressure on the lower body, they most frequently develop in the calves. Trunk varicose veins are near the skin surface and are thick and knobbly; they are visible and often very long. Reticular varicose veins are red and are sometimes grouped together into a network. Telangiectasia varicose veins, a.k.a. thread veins or spider veins are small clusters of blue or red veins that can appear on your face or legs. Women are more likely to be affected by varicose veins than men because female hormones tend to relax the walls and valves of veins. Risk increases if a close family member has varicose veins. As you get older, your veins start to lose their elasticity and valves inside them become less efficient. Being overweight puts extra pressure on your veins and valves, as they have to work harder to send the blood back to your heart. The impact of body weight on the development of varicose veins is thought to be more significant in women.