Kidney function

Most people have two kidneys and despite their relatively small size,
they receive approximately 20 per cent of the blood leaving the heart.
They're bean-shaped organs, the size of a fist, weighing about 150g.
They're located near the middle of the back, just below the rib cage,
one on each side of the spine. The right kidney sits just below the
diaphragm andbehind the liver; the left below the diaphragm behind the
spleen, and is slightly larger.
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What do your kidneys do?
Healthy kidneys clean your blood and make hormones that keep your
bones strong and your blood healthy.
Each kidney has a million tiny filters, called glomeruli. They filter
about 200 litres of blood per day, sifting out about two litres of
waste products (including excesssalt) and extra water.
The wastes and extra water that's left becomes urine, which flows to
the bladder through tubes called ureters. The bladderstores urine
until releasing it during urination, and the cleansed blood returns to
the heart and recirculates through the body.
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Fluid balance
By removing just the rightamount of excess fluid, healthy kidneys
maintain what is called the body's fluid balance, meaning the correct
amount of water stays in the body.
In women, fluid content stays at about 55 per centof total weight, in
men about 60 per cent. The kidneys maintain these proportions by
balancing the amount of fluid that leaves the body against the amount
entering.
Blood pressure is closely related to water balance; the more water
there is inthe body, the higher the blood pressure.
Fluid comes into our bodies from what we drink, and from high-liquid
foods such as soup. If we drink a lot, healthy kidneys remove the
excess fluid and we pass more urine. If we don't drink enough, or it's
a hot drink, the kidneys retain fluid and we don't pass much urine.
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Other functions of the kidney
Healthy kidneys also produce a range of hormones, including:
*. Erythropoeitin (EPO), which is carried in the blood to the bone
marrow where it stimulates the production of red blood cells. These
cells carry oxygen throughout the body.
*. Renin and angiotensin, that regulate how muchsalt and fluid the
body keeps, and how well theblood vessels can expand and contract.
This, in turn, helps control blood pressure (as well as the effects of
the kidney on fluid balance).
*. Clacitriol (Vitamin D) is activated by the kidneysand controls the
amountof phosphate and calcium in the bones and blood.
Many drugs are removed from the body through secretion by the kidney
into the urine. The kidney also breaks down certain proteins and
creates glucose when you are fasting.
When kidneys fail, harmful wastes build up in your body, your blood
pressure may rise, and your body may retain excess fluid; leading to
ankle swelling and shortness of breath (water in the lungs). Lack of
EPO causes tiredness due to anaemia and lack of active Vitamin D
causes bone pain, and occasionally fractures./