FOR SENIOR HIGH SCHOOL

1. Excretion in humans
IGCSE BIOLOGY
OXFORD MANOR COLLEGE ABUJA, NIGERIA
INSTRUCTOR: MR MATHEW

2. What is Excretion?
• Excretion is the removal of toxic materials,
the waste products of metabolism and
excess materials.
• Metabolism means the chemical processes
going on in the body.
• One type of waste is not excreted from the
body - faeces! It is egested (the removal of
undigested food)
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3. Substances that needed to be excreted
substance source Organ of
excretion
Effect
Carbon dioxide Respiration in living cells Lungs Excess carbon
dioxide is toxic.
Urea, nitrogenous
waste
Breakdown of excess amino
acid by the liver
Kidney
Excess salt and
water
Food and drink Kidney and
skin
Bile pigment,
bilirubin
Breakdown hemoglobin liver
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4. • It is necessary for the body to rid itself of waste
products.
• It is also important to regulate the volume and
composition of body fluids.
• The excretory systems of the body do this.
• All vertebrate animals produce nitrogen waste
(urea) in one form or another. Your kidneys
filter out urea to produce urine, removing
nitrogen waste from your body.
• Kidneys also regulate water levels by excreting
different amounts of urine.
• Your lungs excrete carbon dioxide and water as
you breathe out.
• Your skin sheds excess salt through sweat.
Substances that needed to be excreted
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5. The human urinary system Kidneys = It produce urine which
contains urea, water and mineral salts.
Aorta = “dirty” Blood enters the
kidneys at high pressure via the aorta
Vena cava = “clean” blood leaves the
kidneys and enters the vena cava.
Renal arteries and vain = help to
supply the kidney with blood
Ureters= urine flow down the ureter
into the bladder
Bladder=were urine is stored until the
sphincter muscle is released.
Urethra = urine flow out of the bladder,
through the urethra to the
environment
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6. Where are the kidneys?
•The kidneys are a paired
organ system that are found
at the back of the abdominal
cavity just above the
umbilicus (belly button!)
•They sit either side of the
spinal column just below the
rib line, they are not
protected by the ribs and can
be damaged by a large impact
force applied to the area such
as a kick or punch.
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7. Function of the kidneys
• The kidneys have a vital role in homeostasis, they control the content of the
blood
• Kidneys act as filters to “clean the blood”
• They perform three main roles
1. Removal of urea from the blood
2. Adjustment of ions in the blood
3. Adjustment of the water content of the blood
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8. Blood enters the kidney
from renal artery
Filtered blood leaves the
kidney through renal vein
Nephron – the filter
Urine leaves kidney
through ureter
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9. Structure of Kidney
Each kidney has four parts:
• Cortex – the outer layer jammed pack full of filters
called nephrons. Filters the blood.
• Medulla – the middle layer which has the tubes
carrying filtered wastes to the centre of the kidney.
Contains Loop of Henle
• Pelvis – area where all collecting ducts come together
and connect with ureter.
• Ureter – transports urine to the bladder.
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10. Pelvis
Medulla
Cortex
Ureter
Renal
vein
Renal
artery
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11. Cortex
Medulla
Nephron
Ureter
Renal artery
R. vein
The unit of a kidney is the
nephron – it carries out
filtering and reabsorption.
There are roughly one million
nephrons in each kidney.
VIEW OF THE NEPRONE
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12. Blood is filtered
in the bowman's
capsule
Reabsorpti
on of useful
substances
at the
convoluted
tubule
Water levels of
urine adjusted
To bladder
PROCESSES OF THE NEPRONE
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13. Proximal convoluted tubule
Loop of Henle Urine collecting duct
Distal
convoluted
tubule
Capillaries off renal
artery
Glomerulus
Bowman’s capsule
Renal artery
• Blood arrives from the renal artery.
• Blood enters a ball of capillaries called Glomerulus.
• Theses capillaries sit in a filter called the Bowman’s
or renal capsule.
• Small molecules leave the capillary and enter the
capsule – glucose, amino acids, salts, urea and
water.
FILTRATION PROCESSES OF THE
NEPRONE
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14. Glomerulus
Bowman’s capsule
Convoluted or
kidney tubule
Urine collecting duct
Distal
convoluted
tubule
Capillaries off renal
artery
Renal artery
• The filtered blood
moves down the
nephron.
• In the convoluted
tubule cells reabsorb
the good stuff –
glucose, amino acids,
most salt and water.
• The rest – water and
urea – moves on
through the nephron.
REABSORBTION PROCESSES OF
THE NEPRONE
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15. Glomerulus
Bowman’s capsule
Loop of Henle Urine collecting duct
Convoluted
tubule
• As the urine moves
on more water is
saved in the loop of
Henle and collecting
duct
• This adjusts water
loss to suit the level of
water in the body.
RELEASE OF WASTE
PROCESSES OF THE NEPRONE
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16. Glomerulus
Bowman’s capsule
Proximal convoluted tubule
Loop of Henle Urine collecting duct
Distal
convoluted
tubule
Capillaries off renal
artery
Renal artery
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17. • Renal artery: brings blood to the kidneys
Contains waste products.
• Renal Vein: takes blood away from the kidneys. Purified
blood
• Convoluted Tubules: reabsorption of useful substances
happens here; including Glucose, most water and some
salts
• Bowman’s Capsule: This is where filtration takes place.
The filtrate contains useable & waste products
• Collecting duct: collects urine from nephrons and
transports it to the pelvis
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18. Composition of Urine
(what its made of)
• Water
• Urea
• NaCl (sodium chloride)
• KCl (potassium chloride)
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19. Formation of Urea
• Excess amino acids cannot be stored in the body.
• The liver breaks down nitrogenous compounds (amino acids
mostly).
• This is called deamination.
• This produces urea which must be removed from the
body.
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20. Deamination process
• The removal of an amino group from a molecule
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21. Deamination process
Amino acid + Oxygen  Carbohydrate + Ammonia
O
O
Used for energy
Toxic
How to get rid of toxic ammonia?
Carbon dioxide + Ammonia  Urea + water
Taken from the liver to the kidney
to be filtered and excreted
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22. Excess Water:
• Water content in blood & body must be kept constant
• If not regulated, the cells will take up water by osmosis
– they will eventually swell up, burst and die
• When the body excretes a large amount of water the
urine is light in colour & dilute
• When the body retains a large amount of water, the
urine is dark & more concentrated
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23. Important Liver
Functions:
• Converts excess amino
acids into urea –
through deamination
• Controls the amount
of glucose in blood,
with the help of the
hormone Insulin
• Stores excess
carbohydrates as
Glycogen
• Makes bile
Breakdown in the Liver
• Liver breaks down old red blood cells.
• Alcohol, other drugs and hormones are
also broken down by the liver – this is
called detoxification.
• Prolonged use of alcohol or drugs like
paracetamol can lead to liver failure.
• Liver also makes bile which is temporarily
stored in the gall bladder. Bile is broken
down and added to faeces.
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24. Function of the Skin
•Although the skins
main function is to
provide a protective
covering, it is also
involved in excretion
•Dissolved salt, lactic
acid & urea can exit
the body via sweat
glands
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25. Kidney disease
• Diabetes causes damage to the small blood vessels in
the kidneys.
• This process slowly destroys the filters and causes
problems due to build-up of the waste products in the
blood.
• The filters start to leak out too much protein into the
urine and this can be the first sign of diabetic kidney
disease.
• High blood pressure can also cause kidney damage
itself.
• Kidney disease may also result from infection, drugs
and kidney stones while some types may run in the
family.
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26. Treating kidney failure
1. Kidney dialysis
• This is the process of removing waste and excess fluid
from the blood using an artificial kidney machine that
filters or washes the blood.
• Blood is collected from a vein in the arm and passes
along a tube that is semi-permeable.
• The dialysis solution on the other side of the tube has
no urea so urea passes out of the blood.
• Treatment is required three times a week, each
lasting about five hours.
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27. Artery
Vein
Blood in
Blood out
Fresh dialysis fluid Used dialysis fluid
Constant temp.
Dialysis fluid
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28. Treating kidney failure
2. Kidney transplantation
• A kidney transplant may
be considered if your
doctor feels that your
general health is good
enough to stand up to
the operation.
• You also need drugs to
suppress the immune
system after surgery. This
is needed to stop
rejection of the foreign
tissue.
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29. • A donor kidney can come from a living person (usually
a blood relative such as a parent, brother, sister or
child).
• Or, from someone who has died in hospital and
permission has been given to use their kidneys.
• The transplant kidney is placed in the groin. Your own
kidneys are not removed.
• After a transplant the person no longer needs dialysis.
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30. Disadvantages of
Transplants
• A good tissue match is needed
for the donor kidney to reduce
rejection.
• Very expensive operation.
• Risk of rejection of the donor
kidney so immunosuppressant
drugs must be taken daily.
• Some religions do not allow
transplants.
Advantages of
Transplants
• Have a normal lifestyle
as no dialysis.
• Dialysis takes several
hours in hospital three
times a week and makes
a person very tired.
• Dialysis machines are
expensive.
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