The Excretory System
Functions
• Excretion - Filtering metabolic wastes
• Wastes
– Excess salts
– Carbon Dioxide
– Urea – produced when amino acids are used
for energy
Skin
• Sweat
– Excess water, salt,
small amounts of
urea
Lungs
• Excrete CO2 when
energy is produced
by the
mitochondria
Liver
• Converts amino
acids to useful
compounds
• Produces urea as
waste
Kidneys
• Remove waste
products from the
blood
• Maintain blood pH
• Regulate water
content of blood
Urinary System
The Urinary Organs:
• Kidneys: filters that
take waste out of
the blood and
make urine
The Urinary Organs:
• Ureters: tubes that
carry urine to the
bladder
The Urinary Organs:
• Bladder: a muscular
bag that collects
urine
The Urinary Organs:
• Urethra: a tube that
carries urine out of the
body
Kidneys
Kidney Regions
Renal
Cortex
Renal
Medulla
Renal
Pelvis
Blood Flow
• Waste-laden blood
enters kidneys through
the renal artery
• Clean filtered blood
leaves the kidney
through the renal vein
Nephron
• Structural units of
the kidney
• Over 1,000,000 in
each kidney!
– 3 cm long
– 0.03 mm wide
• Filter the blood
• Reabsorb water,
glucose, and salt
Glomerulus
Nephron
Glomerulus
Loop of Henle
Bowman’s Capsule
Filtration
• Blood pressure
forces blood
through the
glomerulus
– All blood is filtered
every 45 minutes
Filtration
• Filtrate
– Water, urea,
glucose, salts, amino
acids, and some
vitamins
• Proteins, cells, and
platelets are too large to
pass through and remain
in the blood
Reabsorption
• Most of the filtrate
reenters the blood
• Active transport
– Amino acids, fats,
glucose
• Osmosis – 99% of
water reabsorbed
Urine
• Forms in Kidneys
– Loop of Henle
• Made up of urea,
excess salts, and water
– Concentration
variation
• Kidney  Ureter 
Bladder
Bladder
• Hollow muscular organ
• Flexible cells
• Nerves tell the brain
when the bladder is full.
– After 200 ml have
accumulated
– After 1 minute reflex
subsides
• Holds approximately
500 ml
Kidney Disease
Dialysis
• http://www.kidneypatientguide.org.uk/site
/HDanim.php