We all know that fluids naturally want to move downwards – there aren’t any rivers that flow uphill! The reason, of course, is gravity. So have you ever wondered why we don’t have to regularly hang upside down to get the blood back from our feet up to our lungs and heart?
It’s the job of our circulatory system to keep blood flowing upwards as well as down, and most of the time, it works just fine. Sometimes though, the power of gravity is too much for even our well-engineered biology to overcome. And when circulation fails, blood can pool in our lower body and lead to over-filled veins that begin to bulge – these are what’s known as varicose veins.
Circulation 101: the difference between veins, arteries, and capillaries
In order to understand why our circulatory system can sometimes fail, you first need to know how it works. The system includes your heart, your lungs, and all the various vessels - i.e. tubes - you have to carry blood around such as arteries (which carry blood away from the heart), veins (which carry blood back to it) and capillaries (the tiny blood vessels which join the two and are responsible for getting blood to each individual cell). This network of large and small vessels is responsible for oxygen delivery, nutrient delivery, and waste removal; if your body were a town, they’d be the roads necessary to allow delivery drivers and garbage trucks to get to everyone’s home.
Your arteries deliver the oxygen-rich blood that your cells need, and when they use it, they create carbon dioxide. Your veins then return this ‘used’ blood back to your heart, from where it’s pumped to the lungs to filter out the carbon dioxide and fill back up on oxygen. Think of it as couriers returning to the warehouse to reload, and garbage trucks heading off to empty before coming back.
And this whole system is kept running by the non-stop pumping of your heart!
Your anti-gravity body: how blood flows up as well as down
Gravity offers both benefits and challenges to your circulatory system. It helps to make light work of pumping blood all the way down to the tips of your toes. But the return path? That’s where the problems can begin.
Blood traveling in your veins must overcome gravity on its arduous climb back to your heart. Especially when it’s coming all the way back from your lower legs, this ‘uphill’ movement poses a difficulty for your circulatory system – and frankly, if your heart alone had to move your blood with zero help, it wouldn’t manage. So the human body, incredible thing that it is, evolved two key adaptations to conquer the pull of gravity.
The extra ‘hearts’ inside your calf
Did you know you have another heart inside each calf? Okay, not really! But there’s a good reason that the soleus muscle located at the back of your calf is often called a ‘peripheral heart’, as well as the ‘calf-muscle pump’. Like the heart, it plays an essential role in keeping things flowing, because your heart is simply too far away from your legs to generate the necessary pressure to push blood all the way back up them.
Every time you take a step, the soleus muscle contracts, meaning it gets shorter and fatter. This compresses the veins deep within your leg – and much like when you squeeze a tube of toothpaste, the blood inside the vein is forced to move upwards. When the muscle relaxes, the pressure on the vein is released, and more blood can flow in from below.
Venous valves for one-way blood flow
So when the soleus muscle relaxes, why doesn’t that blood that just got squeezed upwards simply fall back down? It’s all down to the other tool your body uses to keep the system running effectively: valves.
Unlike arteries, veins are divided into a long row of smaller sections, blocked off from each other by a series of one-way valves. The valve has two flaps that point slightly upwards so that they can be easily pushed open from below, but not from above. Pressure from underneath the value opens it up to allow blood through, and when the pressures eases, the flaps fall back down and cover the gap once more, effectively closing the valve to prevent blood from flowing back to where it just came from.
What causes venous valves to weaken?
To perform properly, every component in your circulatory system needs to be operating effectively. As with all systems, the strength is limited by its weakest link. And when it comes to the venous system, the part that tends to fail the easiest is the one-way valves.
Rarely, and possibly due to genetics, people can actually be born without venous valves. More commonly though, these valves get weaker or wider due to ageing or hormones, until they’re no longer able to seal off the vein section completely between heartbeats or ‘calf squeezes’. This makes them less effective at preventing blood from flowing back down.
Perforating veins, which connect superficial veins by the skin’s surface to ones deep in the leg, are thin-walled and have many valves, which makes them particularly prone to developing valve problems.
So, what actually causes varicose veins to develop?
How weak valves lead to bulging veins
Varicose veins form when blood begins to collect inside the veins, usually because the venous valves have stopped working correctly. No longer able to fully prevent blood from flowing backwards, gravity wins and the blood pools in a section of vein below the faulty valve(s), caused it to become enlarged.
Often appearing dark purple or blue, varicose veins are visible below the skin and might look swollen, lumpy or twisted. Veins that are located furthest from your heart are the most likely to be effected, such as those in your lower legs.
Weakened valves – and hence varicose veins – may be caused by genetics or simple ageing, but can also occur due to pregnancy, when the body creates more progesterone. This hormone relaxes the vein walls which, combined with the increased blood volume and pressure that occurs at this time too, makes it much easier for a valve to fail.
Another contributor to varicose veins in the leg is the simple fact that walking and standing places increased pressure on the veins in the lower body, due to gravity. (Conversely, putting your legs up above your heart would reduce the pressure). As do conditions that place pressure on your abdomen such as constipation and certain tumors.
Inactivity causes varicose veins too!
However, as we’ve explained, valves are only one half of the body’s anti-gravity arsenal. While it’s unlikely that a soleus muscle will ever ‘go wrong’, if you’re not walking (or otherwise exercising that muscle), it’s just not helping.
So during prolonged periods of inactivity – such as sitting down for a long-haul flight or desk job, or being confined to a bed due to illness or injury – when the soleus muscle isn’t pumping, your valves have to do all the work on their own. And under that extra strain, it’s easier for them to malfunction.
Is there a solution to varicose veins?
Varicose veins affect about one in every five adults on the planet, and more than two in five women aged 50 and above. So if you’re suffering from them, know that you’re not alone – and plenty of effort has been put into finding treatments and solutions!
Graduated compression socks and graduated compression pantyhose can reduce the severity of varicose veins and even prevent them from developing in the first place, by helping to keep blood flowing upwards. They do this by applying comfortable pressure that gets firmer the further down the leg you go, to make it harder for blood to move downwards even if your valves aren't fully sealed.
Of course, if you experience any difficulty with what you suspect are varicose veins, visiting your physician is always a sensible step towards finding ways to prevent them from worsening or to find relief from the swelling and discomfort. Chances are, they'll recommend compression hosiery!