Le milieu intérieur
The kidney has never enjoyed the metaphoric power of the heart, in any literature, in any language, at any point in time.
Yet rightly considered, the kidney is the very stuff of philosophy.
While you are reading quietly in your armchair by the fireplace, your heart, that simple, sturdy, vulnerable pump, sends around 5 litres of deep red oxygen-rich blood every minute, to every niche and cul de sac of your body. One litre of that precious elixir, a fifth of the total, flows through your kidneys. Every minute.
Each kidney holds a million tiny filters, the glomeruli (a Latin word for tiny wonderful round globules) measuring around 250 µm in diameter. They work unceasingly, day and night, to sort out what must be retained – the blood cells, the larger proteins – and what must be examined further to get the balance just right. The cells and proteins start on their solemn onward procession back to the heart. The salts and waters filter down further into the meat of your kidney, into a complex, bewildering web of tubules, loops and collecting ducts. There key decisions are constantly beiong made – how much water, what salts can be retained. What you need is added back into the mix returning to the heart. What you don’t need – toxins, drugs, the waste products of metabolism – all sail downwards to your bladder and thence to the outside world whence they came. The extra gram or so of sodium chloride in the pistachios you ate with your preprandial single malt. The pint of water so sweetly interlaced within a pint of Theakston best bitter lasts only a few minutes in your body - the filters kick into gear, the decision is made in the tubules to let the extra water go through to the keeper without offering a shot, and before you know it, the water is gone (while the warm inner glow persists).
So, you see, the kidney is defining very precisely your internal chemical composition your mileu intérieur, the complex personal soup which makes you quite different from the outside, uncaring universe.
The French father of physiology Claude Bernard (1813-1878) surely put it best, first defining a key philosophical concept - homeostasis:
‘La fixité du milieu intérieur est la condition de la vie libre et indépendante.’
‘The constancy of the internal environment is the condition for free and independent life.’.