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The Excretory System
• Function:
– Removal of metabolic wastes and excess
substances from cellular activities that build
up in bodily fluids
• This is not egestion which is the removal
of undigested food or feces
Major Metabolic Wastes
• Carbon Dioxide
– produced from cellular respiration
• Nitrogen Compounds
– produced by the breakdown of amino acids
– Ammonia, urea, uric acid
• Mineral Salts
• Water
Disposed of in urine and sweat
Organs of Excretion
• These organs work with the circulatory,
nervous and endocrine systems to help
keep the body’s internal environment
constant and maintain homeostasis
The Kidneys and the
Urinary System
• Composed of:
– Kidneys
– Ureters
– Bladder
– Urethra
• Summary:
– Kidneys produce urine
which passes to a tube
called a ureter
– Urine flows to the urinary
bladder where it is stored.
– During urination the stored
urine travels from the
bladder to the outside of the
body through the urethra
– Helps to maintain a proper
fluid balance in the body
Structure of the Kidney
– Cortex: outer part
where blood is filtered
– Medulla: middle part
made up of tubes called
collecting ducts that
carry filtrate to pelvis
– Pelvis: inner region
connected to ureter
Kidney Function
Filters the blood
Primary organ of “Osmoregulation”
(regulating water balance)
The Nephron
• Part of the kidney where filtering of the blood
– Each kidney has over a million nephrons
– Part of nephron lies in cortex, part in the medulla
Filtration and Reabsorption
in the Nephron
Renal vein
Bowman’s Capsule
Loop of Henle
Collecting duct
for urine
Parts of the Nephron
• Glomerulus:
– group of capillaries
in a tight ball at end
of nephron
– Where substances
filter out of blood and
enter nephron as
• Bowman’s
– cup shaped structure
that surrounds the
glomerulus and
receives filtrate from
• Loop of Henle
(Renal Tubule)
– Long loop of the
– Surrounded by
– Reabsorption of
certain parts of
filtrate back into the
bloodstream takes
place here.
from filtrate
How is Urine Formed?
• Process of filtration and reabsorption
– Filtration of materials from blood
– Reabsorption of certain useful substances
• Filtration:
– Blood enters kidney
under pressure forcing
filtrate through thin walls
of glomerulus into
Bowman’s Capsule
– Filtrate:
• Composed of water,
urea, glucose, amino
acids, various salts
• But:
– We need a lot of this fluid back!
– Otherwise we lose too much water, glucose
and salts
– On average about 180 liters of filtrate is
formed in 24 hours but only 1 to 1.5 liters of
urine is produced!
• Reabsorption:
– takes place in renal
tubule (Loop of Henle)
– Returns 99% of filtrate
back to the blood
• Most of the water
– By passive transport
• Glucose, amino acids
and most of the salts
– Mostly by active
– Way to conserve water
– Way to keep nutrients like glucose and amino
– Filtrate becomes very concentrated as urine
• Urine: made of urea, water and excess
• Interactive showing Nephron Function and
what is filtered and reabsorbed:
• The Excretory System and The Nephron
Regulation of Urine Output
• Hypothalamus (small area of brain)
– Secretes hormone called ADH (antidiuretic
• Fluid intake low = ADH secreted
– Stimulates reabsorption of water in nephron.
– Urine output decreases and is more
• Fluid intake high: ADH not secreted
– Less reabsorption of water in nephron
– Urine output increases and is relatively dilute
Kidney Disorders
• Kidney Stones:
– found when
substances crystalize
out of urine
– may may block kidney,
ureters, bladder
• Uremia:
– urine and other
wastes are not
filtered out of blood,
poisoning cells
• Kidney Dialysis:
– when the kidneys
fail, excess fluids
and wastes
accumulate in blood.
– use artificial kidney
to filter blood
• Gout:
– uric acid crystals are produced and accumulate
in joints
– Similar to arthritis
• Crash Course on the Excretory System
• Tutorials on Kidney and Nephron Function:
The Liver
• Helps to filter the blood and regulate
the makeup of body fluids
• Detoxifies Blood
– Removes substances such as drugs, alcohol and
certain toxins from the blood
– Changes them to an inactive form which is excreted
from the body by kidneys
• Breaks Down Worn Out Red Blood Cells
– RBCs don’t have nuclei and don’t live very long
– Part of the hemoglobin molecule is found in bile.
• Excretes Bile:
– the liver synthesizes and excretes bile into gall
bladder to add in fat digestion
• Forms Urea
– Excess amino acids from protein digestion are
broken down in the liver by deamination.
– Deamination:
• “amino group” is removed from amino acid
• changed to ammonia NH3
• ammonia is toxic to the body and is changed into urea
in the liver
– Kidneys filter out urea in the nephron and excrete
it from the body in urine.
Diseases of the Liver
• Cirrhosis:
– disease caused by
overloading liver with
harmful materials
such as alcohol
– Liver becomes
enlarged and
overgrown with
excess tissue
• Jaundice:
– Bile is not secreted properly
– Reabsorbed hemoglobin fragments form
bilirubin in the blood and make the skin look
jaundiced or yellow
• An excretory organ
• Give off carbon dioxide, and excess
water both metabolic wastes.
• Gives off sweat or
perspiration to help regulate
body temperature.
• Sweat is composed of 99%
water, salts and some urea.
• Also capillaries close to skin
surface help to eliminate or
conserve heat.
• Skin is the largest organ of
the human body.
• It protects the inner organs
and tissues of the body, and
has sensory cells to help us
detect changes in our
• It also has sebaceous
glands that produce oil that
help protect skin and keep it
soft and pliable.
Comparative Excretory
Systems in Animals
Excretion in Protists and Hydra
• Direct contact with cell
membrane and environment.
• Wastes diffuse out of cell
membranes or are excreted
through active transport
• Metabolic wastes include:
carbon dioxide, ammonia and
mineral salts
• Ammonia is the chief
nitrogenous wastes of protists
• Freshwater protists use contractile vacuoles and
active transport to remove excess water that is
constantly entering the cell by osmosis.
• Concentration of water greater outside cell than inside
so it moves across membrane by diffusion into cell.
• Salt water protists don’t have this problem.
Excretion in Earthworms
• Pairs of nephridia found in almost every segment
– Surrounded by capillaries and filter wastes from blood
– Wastes form a dilute urine which passes through a bladder
and out through the nephridiopore.
• Urine is water, mineral salts, ammonia and urea.
Don’t Forget!
• Thin outer skin is the respiratory surface
– Below skin are capillaries carrying blood with hemoglobin
• Live in moist soil and constantly secretes mucus to
keep skin moist
– If exposed to air and dries out it will suffocate
Excretion in Grasshoppers
• Malpighian tubules are bathed by blood from open
circulatory system
– Wastes enter tubules and pass into intestine
– Water and other useful substances are reabsorbed and
returned to body fluid
• Dry nitrogenous waste product: uric acid
– Helps conserve water
Don’t Forget!
• System of tracheal tubes for
gas exchange
– Branching air tubes carry air
directly to cells
– Muscle contractions pump air in
and out of tubes
• Spiracles: outside openings
that lead to tracheal tubes