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The job of the excretory system is to remove metabolic wastes from your body.
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Metabolic wastes are those that are created by the life processes within your cells.
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Remember that the wastes removed from your body by your digestive system (Feces) are not considered metabolic wastes.

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For this organ system, 4 is a magic number to remember.
For instance, there are 4 metabolic wastes created by your body.
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Water
Carbon dioxide
Salts
Urea

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Not only are there four metabolic wastes, there are 4 organs* that remove these wastes.
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Skin Lungs Liver Kidneys*
*(There are actually 4 components which make up our urinary system.)
1. Kidneys
2. Ureters
3. Urinary bladder
4. Urethra

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The largest organ in your body, the skin gets rid of metabolic wastes in the form of sweat.
Sweat consists of water, salts and urea.
The sweat is formed in specialized sweat glands in your skin.

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While your liver does not excrete anything from your body, it is responsible for filtering your blood and forming a nitrogenous waste called urea.
Once formed, the urea is then secreted back into your blood.
It’s molecular formula is (NH
2
)
2
CO
2
Thought question: Since Urea is a nitrogenous compound, from which component of human nutrition is this waste derived from?

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Your lungs help to get rid of two metabolic wastes:
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CO
2
H2O
Normal lung
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These wastes diffuse from the capillaries in your
Lung Cancer alveoli.
Emphysema Lung

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This system consists of 4 components.
1. Your Kidneys: You kidneys filter your blood and remove Urea, excess water and salts. These are combined to form Urine.
2. The ureters are tubes that transfer urine from the kidneys to the urinary bladder.
3. The urinary bladder is a temporary holding sac for urine.
4. The urine leaves your body through your uretha.

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Please turn over your note worksheet and try to answer the following questions.
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1. Name the four metabolic wastes.
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2. Name the four organs involved in excretion.
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3. Where are metabolic wastes created?
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4. Which chemical reaction(s) in your body produces water?
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5. Which chemical reaction produces salt?

Organ
Skin
Liver
Lungs
Kidneys
Function/Wastes excreted
Excretes water, salts and urea in the form of sweat.
Filters blood of nitrogenous wastes and creates Urea.
Excretes water and carbon dioxide during exhalation.
Filters blood of Urea, Salts and water and creates Urine. Secretes urine with help from the ureters, urinary bladder and urethra.