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Chapter 12

Key Concepts

Compare the methods of excretion earthworms and grasshoppers.

Describe the roles of the liver, kidneys, lungs, and skin in human excretion.

Predict which areas of the skin have the most sweat glands.

Key Words






Malpighian tubules



Urinary bladder

Adaptations for Excretion
Section Objectives

Describe how excretion helps maintain homeostasis.

Explain how metabolic wastes are removed from protists and hydra.

Compare the excretory structures of the earthworm and grasshopper.


Must remove metabolic wastes from body.

If not, organisms dies.

Definition: Process by which wastes and excess substances are removed from an organism.

Also removes excess heat

Helps keep body temperature constant

Organs are : lungs, kidneys, liver, skin

Works with other systems to keep homeostasis.

Major Metabolic Wastes

CO2 – formed during cellular respiration ( DS )

H2O– formed during cellular respiration ( DS )

Nitrogen compounds

ammonia, urea, uric acid

Mineral salts

NaCl, KSO4

All others poisonous at high levels

Excretion is not elimination or defecation of feces

Excretion in Protists

Simple process

Diffusion out through cell membranes into surrounding environment


Carbon dioxide

Mineral salts

Ammonia ( NH 3 )

Soluble in water

Ameba and paramecium

Active transport


Contractile vacuoles

Water ejected from cell

Excretion in Hydra

Freshwater organisms

Diffusion directly into water environment

Water enters by osmosis

No contractile vacuole, so pumped out through cell membrane

Active transport

Excretion in Earthworms

Has organs


Found in pairs

One on each side

Body fluid enters nephrostrome

Funnel shaped opening

Cilia beat to move fluid to each segment

Reach opening, large bladder

Drains to outside by nephridopore

Urine – dilute solution consists of water, mineral salts, ammonia, urea

Urea = ammonia and CO 2

Soluble in water



Since the earthworm lives in a moist environment, it has no problem excreting the soluble nitrogenous wastes ammonia and urea. The production of large amounts of urine – about 60 % of the earthworm’s body weight each day – results in the rapid removal of the highly toxic ammonia.


Malpighian tubules

Open circulatory system

Diffusion and active transport

Uric acid, feces through anus

Uric acid does not dissolve in water

Secreted as solid or semisolid

Saves water

CO2 diffuses from body tissue into tracheal tubes



12-1 Section Reviews
Today’s Quiz: Put all answers on loose-leaf

1. What is excretion ?

2. List the major metabolic wastes.

3. Why does excretion in the earthworm require specialized organs?

4. What animals excrete uric acid, and how does it help them?

5. Order the following nitrogenous waste products from least to most poisonous: urea, ammonia, uric acid.

Human Excretory System
Section Objectives

Identify the principle metabolic wastes of the human body.

Describe the excretory functions of the liver.

Draw and label the parts of the human urinary system, and describe the process of urine formation.

Explain the excretory functions of the lungs and skin.

The liver is the largest internal organ and is an important organ in the human excretory system.


Purifies the blood

Changes harmful substances into inactive and less poisonous forms.

Substances returned to bloodstream and finally excreted from body by kidneys.

Disease called cirrhosis

Causes death

People at Risk

Junk Food

Coffee drinkers



Exhaust from cars

Birth control pills

Candida Patients


Chronic pain sufferers

Exposed to pesticides

Exposed to Heavy metals

Gas station workers

Auto mechanics

Long term prescription drug therapy

Athletes using steroids

Excretion of Bile

Made by liver

Contents: bile salts, cholesterol, hemoglobin parts from worn out RBC

Some parts metabolic wastes

Collects in gall bladder pass through bile duct to small intestines

Helps digest and absorb fats

Leaves body in feces


Yellow skin

Formation of Urea

Ammonia is converted to urea by a series of reactions called orinthine cycle.

The cycle begins when one molecule of ammonia and one molecule of carbon dioxide combine with one molecule of orinthine ( 5 carbon amino acid ) to form citrulline ( 6 carbon amino acid ).

Citrulline combines with another molecule of ammonia to form arginine ( 6 carbon amino acid ).

Arginine is hydrolyzed, forming ornithine and urea. The ornithine is reused in the cycle.


The Urinary System

Made up of:

2 kidneys


Urinary bladder



Inside Your Kidney
Diagram showing the parts of the kidney and the nephron

Kidney Processes


Kidney ( s ) stops working:

Artificial kidney machine may be used to filter blood.



Rid body of carbon dioxide and water ( in the form of water vapor )

Cellular respiration ( Ch. 11 )

The Skin

As you already know, sweat comes out of pores in your skin.  As you may not know, sweat is a mixture of three metabolic wastes: water, salts, & urea.  So as you sweat, your body accomplishes two things: 1) sweating has a cooling effect on the body, and 2) metabolic wastes are excreted.

Functions of the Skin


out microorganisms and foreign materials

Skin from drying out

Because it is waterproof

Secretes small amounts of urea and salts in sweat

Major role remove excess heat

Blood vessels open wider

Flushed appearance

Sweat evaporates

Cools body

Keeps heat in when cold

Blood vessels narrow

Body sweats less

12-2 Section Reviews
Today’s Quiz: Put all answers on loose-leaf

1. Name the organs of excretion in humans.

2. Name the parts of the urinary system.

3. Describe the two stages involved in the formation of urine by the nephron.

4. In what way is the nephron’s filtrate different from urine?

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