(6) More on controlling ion
concentrations and removing waste products
and the problems resulting from malfunctioning kidneys
and kidney failure (plus mention of associated liver function)
The ions essential for life are
absorbed into the blood stream in the gut from digested food.
If the water or
ion content of the body is wrong, too much water may move into or out of the
cells and damage them.
content of the body – ions are lost via the skin when we sweat (you can
taste it on your skin) and
excess ions are lost via the kidneys in the urine.
For example, the kidney controls
the sodium ion (Na+) concentration from digested food containing
Any excess of any ion needs to
be removed e.g. by the kidneys and subsequent excretion of urine.
Water and ions, such as sodium (Na+) enter the body when we eat and drink
and are then absorbed into the bloodstream.
Any imbalance in the ion
concentrations of the cells will result in the wrong quantity of water being
absorbed by osmosis and this reduces the correct functioning of the cell.
It is the kidney maintains the ion
concentration balance in your blood.
If the ion or water content of the
body is not right it can upset the balance between ions and water. It
can result in too little or too much water being absorbed into the cells
by osmosis. The wrong amount of water in cells damages them inhibiting
their normal function.
Ions are lost in sweat, but this is
not a regulated system, which is why the correct balance of ions is
maintained by the kidneys.
The appropriate amount of ions is
reabsorbed into the blood after filtration in the kidney and any excess
ions removed from the body in the urine.
As already described, humans need to remove waste
products from their bodies to keep their internal environment relatively
Know and understand that waste products that have to
be removed from the body include urea, produced in the liver
by the breakdown of amino acids and removed by the kidneys in the urine,
which is temporarily stored in the bladder.
We take in protein in our food e.g.
meat and cheese, which is broken down into amino acids (H2NCHRCOOH,
R is variable). The amino acids are then converted (via
coding) into the proteins we actually need.
we cannot store amino acids in our body, so the excess must be dealt
with in some way. The amino acids can be converted into fats and
carbohydrates (C, H and O compounds) which can be stored in the body,
but neither of these groups of molecules contain nitrogen - whose excess
must be removed in some way by the liver and kidneys.
conversion occurs in the liver (can also be done by the kidney) and involves a process called deamination.
Toxic ammonia (NH3) is produced as a
waste product of the process and this must be converted by the liver
into non-toxic urea, formula O=C(NH2)2.
The urea is soluble and transported to the kidneys, where it can be
filtered out and excreted from your body in urine.
Summary of the three primary kidney functions in terms of cleaning the blood of waste products and maintaining
the correct concentrations of various substances.
(i) The kidney removes urea, formed
from the waste of excess amino acids.
The body can't store proteins,
so excess amino acids are converted into storable fats and carbohydrates and
the waste product of the process is urea.
Urea is a poisonous substance so
on its release from the liver into the bloodstream it is filtered out by the
kidneys before storage in the bladder prior to excretion in urine.
(ii) The kidney adjusts the water content of
the blood e.g. to avoid you becoming dehydrated.
(iii) The kidney also adjusts the concentration of
ions like sodium (Na+), potassium (K+) and chloride
(Cl–) in the blood.
A healthy kidney
produces urine by:
first filtering the blood,
excess ions such as sodium are removed, though some ions are lost in sweat,
reabsorbing all the sugar,
reabsorbing the dissolved ions needed by the body,
reabsorbing as much
water as the body needs,
releasing urea, excess ions and water as urine.
Obviously, if any of the above functions of the kidney
are not working correctly
there will be problems! So, some notes on malfunctioning kidneys
and kidney failure
Urea, the waste product from
excess amino acids, is released by the liver and filtered out by the kidneys
and excreted via the bladder in urine.
People whose kidneys do not
function properly may die because toxic substances accumulate in their
If the kidneys are not working
properly-efficiently then potentially toxic substances including
ammonia can build up
in your blood stream and your body is unable to deal with the
If you lose your ability to
control the levels of ions and water in your body it can have fatal
If kidney function deteriorates to
the point of complete kidney failure your life is in danger.
Their lives can be saved by
using dialysis machines or having a healthy kidney transplanted.
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