1. EXCRETION
WHAT IS EXCRETION?
Learning Objective:
Define excretion and explain the importance of removing nitrogenous
and other compounds from the body.

2. WHAT IS EGESTION?
• EGESTION is the
removal of undigested
material from the
alimenary canal.
• The undigested
material is not formed
in body cells and has
never been absorbed
into the cells.
• Undigested material is
not a product of
metabolic processes.

3. WHAT IS SECRETION?
• SECRETION in the process involved in producing and
releasing useful substances from the cells.
• Example: digestive juices, hormones, sweat, milk

4. WHAT IS EXCRETION?
• EXCRETION is the process
by which metabolic waste
products and toxic
materials are removed
from the body of an
organism.

5. METABOLISM
CATABOLISM ANABOLISM METABOLISM
Chemical Chemical The sum of
reactions in reactions in all the
which which simple chemical
complex substances reactions
substances are built up within the
are broken into more body of an
down into complex organism
simpler ones. substances.

6. METABOLIC WASTE PRODUCTS
• Carbon dioxide
• Excess mineral salts
• Nitrogenous waste products
• Mainly urea (indirectly from deamination of amino acids)
• Uric acid (from breakdown of nucleic acids)
• Creatinine (from breakdown of muscle tissue)
• Excess water
• Bile pigments (from breakdown of haemoglobin)

7. Excretion product/waste Excretory organ Excreted as
Carbon dioxide Lungs Gas in expired air
1. Excess mineral salts Kidney Excreted in urine
2. Nitrogenous waste
products Skin Excreted in sweat,
• Urea from deamination of but small
excess amino acids quantities of
• Uric acid from breakdown nitrogenous waste
of nucleic acids product in sweat
• Creatinine from breakdown
of muscle tissue
Excess water Kidney Excreted in urine
skin Excreted in sweat
lungs Water vapour in
expired air
Bile pigments Liver Excreted through
faeces

8. IMPORTANCE OF EXCRETION
• Metabolic reactions produce metabolic waste
products.
• If these waste products accumulate in the body,
they can become harmful.