Thursday, 16 September 2021

Kidneys are the body’s miniature control room

THERE are countless examples of human inventions inspired by nature in a field known as biomimetics.

From the wings of a plane to various adhesives modelled on the lining of gecko feet, nature’s clever solutions help us to develop our own technologies.

In fact, Gustave Eiffel based the criss-crossing network of metalwork in his famous tower on the minute bone fibres of the human femur.

It should come as no surprise then that the kidneys are no different when it comes to inventive inspiration.

In fact, so exemplary are they at filtering our blood of impurities and waste products that, as I write, a team of researchers in Singapore is working on a membrane-based water purification system that mimics the way the membranes in the kidneys filter our blood to make low pressure, and therefore cheaper, versions of those already in existence.

Of course, the work of the kidney is far more efficient and complex than anything we have yet created ourselves.

This filtering of our blood is the best known function of our kidneys and is vital for life.

In essence, the kidneys are made up of countless miniscule blood vessels that squeeze fluid in and out of tubes that run alongside, taking waste products and electrolytes no longer needed into urine for us to get rid of.

If one delves deeper though into its other achievements, we see that there is more to these characteristically shaped organs than meets the eye. They are certainly not just glorified sieves.

There is a tremendous amount of blood flow to the kidneys. In fact, in a single hour, the kidneys receive around 68 litres of blood and manage to filter about 200 litres a day.

Because of their intricate connection with our circulation, they are well placed to contribute a significant role in the control of our blood pressure.

If, for example, our blood pressure drops, the kidneys notice this from the reduced blood flow around them and so produce a cascade of chemical messengers.

Some of these cause our bodies to retain more fluid in the blood and others constrict our vessels in an overall combined process that brings the blood pressure back up.

Fortunately, this system can also be reversed should our blood pressure be too high so is often a target for the various blood pressure medications at our disposal.

The kidneys don’t stop there though. Our bone health is intimately linked to how they function.

By producing a hormone called calcitriol, which is an activated form of vitamin D, they help the absorption of calcium in our intestines - vital for bone formation and development.

If they sense low oxygen levels in our blood, they can produce another hormone called erythropoietin which stimulates the production of oxygen carrying red blood cells (erythrocytes) to boost those levels.

The kidneys are essentially like mini-control rooms that keep the balance of everything in our bodies just right — a vital process known as homeostasis.

It is rather convenient then that we have two kidneys. It is not the only organ we have two of but why some and not others?

This is a tricky question to answer. The liver is one of a kind, as is the heart (although octopuses have two ancillary hearts to help out the main one) yet we have two lungs, two eyes and two kidneys.

Whereas the lungs bud from a single source, the kidneys develop separately and this is likely an evolutionary step that has carried on from a very early stage in our evolutionary history.

Either way, it means that if one kidney is damaged or removed in some way, we are able to function perfectly fine with the remaining one. In Greek, kidneys were known as “nephros”, hence the name for the study of kidneys, nephrology. This is a vital part of medicine, not least because of the wider impact on the body, as explained above.

When we think about problems with kidneys, most likely one will think of dialysis. This is the process of artificially filtering the blood through complex machines when the kidneys are unable to do so themselves.

This is a remarkable feat of medical engineering, first developed by Dr Willem Kolff in 1943.

Since then, the technology has come on leaps and bounds and there are now about 30,000 people on dialysis in the UK alone but it is needed in those with only the most severe kidney disease.

There is an umbrella term known as chronic kidney disease that can often be quite alarming to hear but actually encompasses everything from the most severe kidney dysfunction to the very mild.

As doctors, we measure various things in people’s blood to check how well their kidneys are functioning.

In general there is a calculated standard of filtration called the estimated glomerular filtration rate, or eGFR, which ideally should be above 90 but is fine below this down to about 60. Any lower and we like to keep a closer eye on things as it can mean that there is a problem.

As we get beyond 50 years of age, there is a steady decline in kidney function anyway but it is good practice to check this more regularly.

If your eGFR does dip below this, your GP might ask you to provide a urine sample to check if any larger proteins are getting through the kidneys’ filter.

Depending on this result, there are certain medications that might help to prevent any further deterioration in your kidney and your GP might ask you to check your blood tests more frequently.

Most often, things remain quite stable but if there is an ongoing decline then sometimes it is worth a trip to the nephrologists.

Although there is a vast array of conditions and problems that can affect kidney function over time, the main culprits are hypertension (high blood pressure) and diabetes.

Managing your blood pressure therefore and preventing diabetes are your best bets in order to retain healthy kidneys.

For those of you with diabetes, a good control of your sugars and blood pressure is even more vital in preventing damage.

This aside, making sure that you are well hydrated is very important – your urine should be straw-coloured and if it is darker than this, it is a sign you are not drinking enough water.

Good hydration also protects against bladder infections and kidney stones, the latter of which is excruciating.

For more information, NHS choices (www.nhs.uk) is a really useful website and has plenty of suggestions for how to reduce blood pressure and prevent diabetes.

• Next time: the skin.

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