Cambridge iGCSE Biology Notes on excretion and the kidneys

1. EXCRETION AND THE KIDNEYS

2. EXCRETION
• The removal from organisms of:
- toxic materials,
- the waste products of metabolism (chemical
reactions in cells including respiration) and
- substances in excess of requirements.

3. Excretion Egestion
• EGESTION:
Is the passing out of food that has not been
digested, as faeces, through the anus.

4. Excretory organs
• Lungs
• Kidneys
• Liver
• Skin

5. LUNGS: carbon dioxide and water
vapour (incidental)

6. KIDNEYS: urea, water, salts, toxins,
hormones, drugs.

7. LIVER: bile pigments.

8. SKIN: water, salts, urea
(incidental losses)

9. EXCRETORY PRODUCTS AND
INCIDENTAL LOSSES
Exretory products Incidental losses
LUNGS Carbon dioxide water
KIDNEYS Urea, water, salts, toxins,
hormones, drugs
LIVER Bile pigments
SKIN Water, salt, urea

10. LIVER
Functions
• Regulation of blood sugars.
• Production of bile.
• Deamination
• Storage of iron.
• Manufacture of plasma proteins.
• Detoxication: breaking down of alcohol, drugs
• Breaking down of hormones.
• Storage of vitamins

11. Alcohol and the liver
• The liver receives all the useful and harmful
molecules that the gut absorbs from food.
• Drugs or poison are harmful molecules.
• Alcohol is a drug. It affects the normal working of the
body.
• It is absorbed from the stomach and liver.
• The cell of the liver convert alcohol in another
substance which does not pass through the rest of
the body´s circulation.

12. Alcohol
• In working to protect other tissues the liver is likely
to harm itself.
• The substance produced from alcohol can be
dangerous to the liver cells in high concentration.
• It can cause a serious disease called cirrhosis.
• If the liver is damaged by excessive alcohol
consumption, then the hole body is affected.
• E.g: Blood glucose concentration cannot be
controlled efficiently.

13. KIDNEYS:
Structure:
- Fairly solid,oval, red-brown and attached to the
abdominal cavity.
- Renal artery: ?
- Renal veins: ?
- Longitudinal section: 3 main parts:
- cortex, medulla and pelvis.
- Leading from the pelvis is a tube, called ureter, which
carries urine that the kidney has made to the bladder.

16. NEPHRON
• Is a single glomerulus (tangle of blood capillaries),
with its renal capsule, renal tube and blood
capillaries.
• Kidneys are made of thousands of nephrons.
• Each nephron begins in the cortex, loops down in
the medulla, back into the cortex, and then goes
down again through the medulla to the pelvis.
• In the pelvis the nephrons join up with the ureter.

17. Kidneys and nephron

18. KIDNEY: FUNCTION
• 1) FILTRATION:
- Blood is brought to the renal capsule in a
branch of the renal artery.
- Only small molecules can go through. They
are squeezed out of the blood into the renal
capsule.
- Water, salt, glucose and urea.
- Most proteins are too big, so they stay
in the blood along with blood cells.

19. KIDNEY:FUNCTION
• 2) REABSORPTION:
- Some of the substances in the fluid in the renal
capsule are needed by the body.
- All of the glucose, some of the water and some of
the salts need to be kept in the blood.
- Usefule substances in the kidney tubule are
reabsorbed and pass back into the blood in the blood
capillaries wrapped around each kidney tubule.
- The remaining fluid continues on its way along the
tubule
- In the collecting duct it is mostly water, with urea
and salts dissolved in it. It is called URINE.

21. THE BLADDER STORES URINE
• The urine from all the nephrons flows into the
ureters which take it to the bladder.
• The bladder stores urine.
• When it is fulled, the sphincter muscle opens
and the urine flows along the urethra and out
of the body.

23. DIALYSIS
• Maintenance of glucose and protein concentration in
blood and diffusion of urea from blood to dialysis fluid,
which has water, glucose, salts that should be present
in the blood. Inside the machine the blood is
separated from the dialysis fluid by a partially
permeable membrane.
• Dialysis does the work of damaged kidneys.
• Patients need to be treated two or three times a week
and the treatment lasts for several hours
(disadvantage
• Application of dialysis in kidney
machines:

26. The best treatment is a KIDNEY
TRANSPLANT but:
THE IMMUNE SYSTEM CAN REJECT TRANSPLANTS:
• The person receiving the transplant is the recipient.
• The person from whose organ the body was taken is the donor.
• The recipient´s immune system recognises the donor organ as
being “foreign”, and attaks it. This is called REJECTION.
• The recipient is given drugs called immunosuppresants. The
trouble is that they stop the immune system from doing its normal
job, so the person is more likely to suffer from all sorts of
infectious diseases.
• The chances of rejection are reduced if the donor is a close relative
of the recipient, because they are more likely to have antigens on
their cells which are simmilar to each other, so the recipient´s
immune system is less likely to react to the donated organ as it
were ¨foreign¨.

27. Successful kidney transplantshave
advantages over dyalisis treatment
• In the long term, a transplant is much
cheaper.
• The patient´s life is less disrupted once they
have recovered from the operation.