EXCRETORY SYSTEM is a collection of organs  the body that helps in removing harmful products in the body before  they become toxic. 

Excretory system

Excretion is the process by which the body removes harmful products from the body before they become poisonous. (Toxic)

2.    The excretory organs include:

  1. Kidneys
  2. Lungs
  3. Liver.
  4. Skin.


There are two kidneys located at the back of the abdomen.

They are bean shaped and reddish in colour.

The major functions of the Kidneys.

  1. Kidneys filter blood in order to remove harmful products which is passed to the bladder.
    1. The kidneys help in controlling the amount of water and salts in the blood.

Substances excreted by the Kidney.

  1. urea.
    1. Uric acid
    1. Excess water
    1. Excess salt.

Position of the kidney.

position of kidney

Structure of the kidney


Functions of parts of the Kidney.

Renal artery

It carries oxygenated blood to the kidneys.

Renal veins

They carry deoxygenated blood away from the kidneys.


It receives blood that should be filtered.

The Pyramid

It contains nephrones that filter blood.

The Pelvis

It receives harmful substances filtered by the kidney.

The ureta

It carries urine from the pelvis to the urinary bladder.

The urinary bladder.

It temporarily stores urine before it is passed out.

The urethra

It passes out urine from the bladder out of the body.

Diseases of the Kidney.

  1. Gonorrhoea
    1. Kidney stones.
    1. Nephritis
    1. Bilharzia
    1. Kidney cancer
    1. Kidney failure/Uremia.

How to care for the Kidneys.

  1. avoid a lot of salt in food.
    1. Avoid drinking a lot of alcohol.
    1. Drink water regularly.
    1. Urinate as soon as you feel the bladder is full. Don’t hold urine for a long time.
    1. Eat a balanced diet
    1. Have regular body exercises.


1.    The lungs act as both the respiratory system and excretory system.

2.    It is an excretory system because it excretes carbondioxide and water vapour.

  2.    It is a respiratory system because it helps the body to get oxygen for the process of respiration.

3.    Respiration is the process by which the body uses food and oxygen to produce energy, water and carbondioxide.

4.    The equation for respiration is

Food + Oxygen = Energy + Heat + Water + Carbondioxide.

Note: Water and Carbondioxide are by products of respiration and the major products are energy and heat

The products of respiration.

  1. Energy
  2. Heat
  3. Carbondioxide.
  4. Water.

Note. Carbondioxide and water are given out when we breathe out. Heat and energy are used by the body.

The respiratory system

respiratory system

Functions of different parts of the respiratory system

The nose

It contains mucus and cilia which help to trap dust and bacteria.

Note: Air is warmed and moistened in the nose.


It prevents foreign bodies from entering the trachea.

Note: If food enters the trachea, choking and coughing will occur to clear the passage.

Trachea (wind pipe)

It conducts air into the lungs

Note: A trachea is made up of cartilages to keep it open.

Alveoli (air sacs)

a.    It is where gaseous exchange takes place.

  • Air sacs are adapted to this function by being surrounded by many blood capillaries and having thin walls.

The pleural cavity

It produces pleural fluid.

Note: The pleural fluid cushions the lungs and reduces friction between the lungs and the ribs.


  1. Breathing is the act of taking in and out of air.
  2. There are two types of breathing:
  3. Inspiration (inhalation) – breathing-in.
  4. Expiration (exhalation) – breathing-out.


What happens when you breathe-in (during inspiration)

  1. The ribs move up and outwards.
  2. The diaphragm flattens to create space for the in coming air.
  3. The volume of  the lungs/chest increases.
  4. Air is drawn-in.

Note:  Inspiration is also known as inhalation.


What happens when you breathe-out (during expiration)

a 1
  1. The ribs move to their original position.
  2. The diaphragm becomes dome shaped.
  3. The lungs go back to their original volume.
  4. Air is expelled.

Note:  Expiration is also known as exhalation.



  1. Gaseous exchange takes place in the alveoli.
  2. The air we breathe-in contains more oxygen than the one we breathe-out.
  3. The air we breathe out contains more carbondioxide than the one we breathe-in.
  4. When air reaches air sacs, oxygen diffuses through the walls of the air sacs.
  5. Carbondioxide in the blood also diffuses into the air sacs and it is eventually expelled through the trachea and the nose.

An alveoli

an alveoli
  • Diffusion is the process by which molecules move from areas of high concentration to areas of low concentration.

Table showing approximate composition of inspired and the expired air

 Inspired airExpired air

Note:  The concentration of nitrogen we breathe in and out does not change because it is not used in our bodies.

Rate of breathing

  1. Under normal conditions, the rate of breathing is always between 10 to 16 times per minute.
  2. The breathing rate increases because there is need for more oxygen for respiration to meet the energy demand of the body.


Factors that can increase the rate of breathing

  1. Physical activity.
  2. Fear
  3. Fright
  4. Diseases related to the respiratory system

Diseases, Infections related to Lungs

  1. Lung cancer
  2. Tuberculosis
  3. Whooping cough
  4. Asthma
  5. Bronchitis
  6. Pneumonia
  7. Diphtheria
  8. Emphysema
  9. Influenza

Lung cancer

  1. This disease destroys the cells of the lungs.
  2. Lung cancer commonly affects smokers and people who work in factories which produce a lot of smoke.


  1. It destroys the lungs especially air sacs.
  2. A person with TB coughs a lot, becomes very thin, sweats a lot and has continuous chest pain.

Whooping cough(pertussis)

Bacteria cause whooping cough.


  1. A person with asthma finds it difficult to breathe.
  2. The air passage is blocked by over production of mucus.



  1. Caused by a virus but worsened by smoking.
  2. This is a disease that affects the air passage.
  3. A person with bronchitis coughs continuously and experiences breathing problems.
  4. This disease is common to people who smoke.


It is an air borne disease caused by a bacteria and it affects both human beings and animals.


          It is an airborne disease caused by a virus.

          (Prevention and control of immunizabe diseases; revise P.5)

How to care for the lungs

  1. Avoid dusty places/Wear nose protective gear when in dusty places.
  2. Do a lot of physical exercises.
  3. Eat meals with a balance3d diet.
  4. Stop smoking and keep away from smokers.
  5. See a health worker in case of respiratory illness.


1.       The liver is a reddish brown organ in the body which removes dead blood cells from the blood.

2.       It receives oxygenated blood through the hepatic artery.

  • It receives digested food from the alimentary canal through the Hepatic portal vein.

Functions of the liver

1.       As an excretory organ, the liver removes dead blood cells from blood for the purposes of making bile.

2.       The liver regulates blood sugar.

  • The liver stores vitamins and mineral salts.
  • The liver detoxicates some poisonous substances in the blood before the kidneys filter it.
  • The liver produces heat that is distributed to other parts of the body.
  • The liver changes the stored fatty into glucose for energy.

Diseases of the liver.

1.       Cirrhosis of the liver (hardening of the liver due to malnutrition).

2.       Hepatitis (a water borne disease caused by a virus)

  • Liver abscess (Boils which form pus in the liver caused by a germ.
  • Liver cancer

Care for the liver.

1.       Avoid drinking a lot of alcohol.

  • Boil drinking water to prevent hepatitis.
  • Eat a balanced diet.
  • Immunization against hepatitis.


1.       The skin is both an excretory and sensory organ.

2.       It is an excretory organ because it excretes salt, excess water and sweat.

3.       The skin has two main layers:

a) The epidermis

b) The dermis.

          The functions of the skin

  1. It regulates the body temperature.
  2. It covers the body to protect it from germs.
  3. It protects the body from serious damage.
  4. It excretes sweat, salt and water.
  5. The skin prevents the body from dehydrating.

The structure of the Skin

execretory system

Parts of the Skin.


1        It is the outer most layer of the skin.

  • it protects the inner layer from harm.
  • It is further divided into three layers in the order of:

a) Conified layer

b) Granular layer.

c) Malpigian layer.

          The Conified layer.

1.       The Conified layer is made up of dead cells which provide protection against harm, bacterial, fungal and viral infection.

2.       It also controls the loss of water from the body since it is waterproof.

          The granular layer.

          It is made up of living cells which die and continue making up the Conified layer.

          The Malpigian layer.

1.       It contains a pigment called melanin, which determines skin colour.

2.       It also gives protection against ultra Violet rays from the sun.

          THE DERMIS

          The dermis is the inner most layer of the skin and it contains the following:

  1. Sweat gland
  2. Sebaceous glands
  3. Nerve endings
  4. Blood capillaries
  5. Fats

Sweat gland

The sweat glands produce sweat which cools the body.

Sebaceous glands

These produce oil which keeps the skin moist, smooth and soft.

Nerve endings

The help in feeling. Eg touch, pain heat etc.

Blood Capillaries.

They carry to and from the skin. The carry food nutrients to the skin, oxygen and other materials the skin will require.


They prevent heat loss from the body. They act as insulators.


  1. Ring worms.
    1. Athelete foot.
    1. Leprosy
    1. Coerns
    1. Skin cancer

Ring worms.

1.       Ring worms are caused by fungus.

2.       It spreads through:

  1. By body contact.
  2. Sharing clothes with infected person.


Scabies is a skin disease caused and spread by itchmites.

Athlete foot

1.       It is caused by a fungus and spread through infested socks and shoes.

2.       It can be prevented by:

  1. Changing socks.
  2. Drying the feet before putting on socks or shoes.
  3. Disinfect shoes and socks with athelete foot powder and spray.


1.       Leprosy is caused by bacilli bacteria and spread through:

  1. Air
  2. Body contact.


1.       They are caused by wearing very tight shoes.

2.       Prevention is by wearing well fitting shoes.

Care for the skin.

1.       Wash your skin/bathe with clean water and soap.

  • Carry out physical exercises for proper functioning of the skin.
  • Protect your skin from sharp and hot objects.
  • Avoid using skin-lightening creams.
  • Wear lose clothes to allow proper aeration of the body.
  • Eat meals with a balanced diet for a healthy skin.

test to do