THE IMPORTANCE OF
EXCRETING WASTES
Many by-products of metabolism are toxic to the
body and need to be excreted
 Example:

Carbon Dioxide (produced during cellular respiration)
is removed by the lungs
 Toxic wastes are removed from the digestive system
by the large intestine
 Alcohol is transformed by the liver into compounds
that can be removed by the kidneys

KIDNEYS

The kidneys play a
crucial role in:
1.
2.
3.
Removing waste
Balancing blood pH
Maintaining water
balance
DEAMINATION
Deamination- the removal of an amino group
from an organic compound
• Most people consume more protein than is
required to maintain tissues an promote cell
growth
• Excess protein is often converted into
carbohydrates
• Proteins, however, contain nitrogen! (and
carbohydrates do not)
The nitrogen atom in a protein is attached to two
hydrogen atoms (amino group)
 This amino group molecule must be removed
from the body
 The by-product of deamination is ammonia
(water soluble gas)

AMMONIA
Ammonia is extremely toxic (0.005mg can kill a
human)
 Fish avoid a build of ammonia by continually
excreting it through their gills
 Since land animals must find a way to store their
waste products, ammonia is not an option

UREA AND URIC ACID
In the liver, two molecules of ammonia combine
with one another and carbon dioxide (another
waste product) to form urea
 Urea is 100 000 times less toxic than ammonia
 Uric acid is another waste product that is formed
by the breakdown of nucleic acids

WATER BALANCE
•
•
•
•
Regulated by the kidneys
Humans may survive for weeks without food
Water, however, is more essential and humans
will die after a few days with no water
We lose about 2L of water a day (urine,
perspiration, exhaled air)
•
Humans must replenish all water lost during the
day
Loss of 1% body water = thirst
– Loss of 5% body water = extreme pain
– Loss of 10% body water = death
–
(Buy a Brita!...or else)
THE URINARY SYSTEM ANATOMY
OVERVIEW OF THE URINARY SYSTEM
•
Kidneys have a mass of about 0.5kg and can hold
as much as 25% of the body’s blood at any given
time
Renal Arteries – branch from the aorta and carry
blood to the kidneys
OVERVIEW OF THE URINARY SYSTEM
Wastes are filtered from the blood by the kidneys
and are carried to the urinary bladder by the
ureters
 A urinary sphincter muscle is located at the
base of the bladder and acts as a valve

When 200mL of urine has been collected in the
bladder, the bladder stretches and nerves send a
signal to the brain
 At 400mL the signal becomes stronger (more
stretching = more signal)
 At 600mL the sphincter releases, urine enters
the urethra and the bladder is voided

STRUCTURE OF THE KIDNEY
•
1.
2.
3.
The kidney has three main structures
The cortex – outer layer of connective tissue
The medulla – the inner layer beneath the
cortex
The renal pelvis – a hollow chamber where the
kidney and ureter is joined
NEPHRONS - ANATOMY
•
Nephrons are the one million slender tubules
that make up the functional units of the kidney
Afferent arterioles – small branches that carry
blood to the glomerulus
Glomerulus – high pressure capillary bed that is
the site of filtration
Efferent arterioles – small branches that carry
blood away from the glomerulus to a capillary net
GLOMERULUS
MORE ANATOMY
Peritubular capillaries – network of small blood
vessels that surround the nephron
Bowman’s capsule – cuplike structure that surrounds
the glomerulus
Proximal tubule – section of the Bowman’s capsule
with the loop of Henle
Loop of Henle – carries filtrate from the proximal
tubule to the distal tubule
STILL MORE
Distal Tubule – conducts urine from the loop of Henle
to the collecting duct
Collecting Duct – tube that carries urine from
nephrons to the pelvis of the kidney