I've seen quite a few people lately suffering from swelling in their legs, many of whom had problems with their veins.
To understand how problems with the veins develop, I have to provide a brief anatomy and physiology lesson. Fresh blood that contains oxygen and nutrients is pumped from the heart to the legs via arteries. The blood then moves across very tiny blood vessels called capillaries - this is where the oxygen and nutrients move out of the blood into the surrounding tissues. Waste products and carbon dioxide then move from the tissues into the capillaries and then into veins for the trip up to the lungs, liver and kidneys where the waste products are removed from the body.
Venous blood would have a hard time moving upward against gravity toward the heart (unless you stand on your head) were it not for two nifty mechanisms. The first is the contractions of the muscles in the legs that push the blood upward like squeezing toothpaste out of a tube. The second is the one-way valves that prevent the blood from moving back toward the feet.
When you understand how the physiology of venous blood flow works, it makes it easier to understand how things can go awry. Gravity is the major obstacle to overcome. People who stand all day long are constantly battling the force of gravity - it is constantly trying to pull blood back toward the feet. This is why our feet tend to enlarge as the day progresses. Obese individuals suffer even more since the additional force of their extra weight on the blood in their veins causes even more swelling.
People who are inactive also tend to have more problems. Since they are not walking around, they don't receive the benefit of muscular contractions to squeeze the blood upward.
The constant effect of gravity on the veins also causes them to enlarge as we age. When this occurs, the valves in the veins become incompetent and leak (see diagram). This results in more blood pooling in the leg veins causing more dilation and more leaking - a vicious cycle leading to unsightly varicose veins.
Pooling of blood in the legs is called venous stasis. The blood can't move upward to have the waste products removed and the leg tissues, especially the skin, become unhealthy and start to break down. This can lead to rashes and itching called "stasis dermatitis," as well as ulcer formation and infections that can sometimes be very serious.
Treatment of venous stasis can be extremely difficult depending on the severity of the condition when he or she presents to the doctor. Sometimes the dilated veins can be surgically removed or closed off with injections.
Less severe cases can usually be treated with compression stockings and elevating the feet above the level of the heart. The stockings provide a force to counteract gravity. People who have developed rashes and ulcers may need to have medicated dressings. Response to treatment can take a long time and may require referral to a specialized wound care center. Serious infections may require antibiotics and surgery. Diuretics (water pills) are not very effective at treating the root cause.
The best way to treat venous stasis is to prevent it in the first place. People who spend a lot of time on their feet, or take long trips in planes, trains or automobiles, should walk frequently or do calf pumps or toe raises to help pump the blood out of the legs. They should also consider elevating the legs above the level of their chest on their breaks and after work. If they can't walk, they should consider wearing compression stockings during their work shift. Good hydration is also important to keep the blood from becoming too thick that may lead to blood clot formation.
Obese people with venous stasis must work on weight loss in addition to the prevention strategies above. I would be remiss if I did not mention that smoking also greatly increases the risk for developing vein deterioration. It also greatly increases the risk for tissue breakdown and ulcer formation due to decreased oxygen delivery.