2. Excretory product Excretory Excreted as
organ
Carbon dioxide Lungs Gas in expired air
Excess mineral salts Kidneys Constituent of urine
Nitrogenous waste products:
1. Mainly urea (indirectly from Skin Constituents of sweat, but
deamination of proteins) only in small quantities for
2. Uric acid (from breakdown of nitrogenous waste products.
nucleic acids)
3. Creatinine (from breakdown of
muscle tissue)
Excess water Kidneys Main constituent of urine
Skin Main constituent of sweat
Lungs Water vapour in expired air
Bile pigments (from Liver Constituent of faeces, via the
intestines
breakdown of haemoglobin)
4. *Excess mineral salts and
nitrogenous wastes
(urea, creatinine, uric
acid) are harmful if they
are allowed to
accumulate in the body.
*
5. *Two main processes are involved in the
formation of urine within each kidney
tubule:
*1. The ultrafiltration of very small
molecules from the blood.
*2. Selective reabsorption of useful
materials.
*
6. *Blood passes from
the branches of the
renal artery into the
glomeruli in the
renal capsules.
*
7. * A protein-rich diet will result in more urea being
present in the urine. This is because urea is formed
when proteins are deaminated in the liver.
* Taking in more liquids or water-rich food increases
the water potential of the blood. Hence, more urine
is excreted. This also happens in cold weather when
sweat secretion is reduced.
* Taking in lots of salty foods will result in the excess
salts being excreted in the urine.
* Sugar can also appear in the after urine after taking
in lots of sugar-rich foods.
*
8. *The water potential of the
blood has to kept relatively
constant because drastic
changes of water potential
can cause serious problems.
*
9. *Osmoregulation is the
control of water and
solute levels in the blood
to maintain a constant
water potential in the
body.
*
10. *The kidneys remove metabolic
waste and control water and
solute levels in the blood. As a
result, the kidneys also play a
vital role in the control of blood
volume (amount of blood in the
body) and blood pressure.
