The Kidney and Urinary System
Kidney Roles
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Kidneys remove waste
from the blood, maintain
blood pH and regulate
osmotic balance in the
body.
We have two of them
because all of these are
important jobs and
constant!
Also, if one fails, we
have a backup.
Water Loss
• Humans’ water
reserves are depleted
faster than their food
reserves.
• We lose 2.0L of water a
day in perspiration,
urine and exhaled air.
• This is under normal
activity levels. Increase
exercise and you
increase the water lost.
Water Loss
 1% lost causes thirst,
 5% lost will bring
extreme pain and
collapse,
 10% lost will cause
death!
Waste Removal
• The liver produces ammonia, urea and
uric acid when it breaks down nitrogen
containing compounds like protein and
nucleotides.
• All of these are toxic and need to be
removed… the kidney is the right organ for
this job.
If you were unicellular…
• Unicellular organisms
use a contractile
vacuole to expel
waste from their
cytoplasm… since
you are not
unicellular, like most
complex animals, you
have an excretory
system.
Human Kidney and Urinary System
Simple Overview
• The kidneys can have as
much as 25% of the
body’s blood at any given
time.
• Renal arteries are what
pass blood to the
kidneys. They have
oxygen and glucose for
the kidney and they are
filled with toxic urea,
ammonia and uric acid.
Simple Overview
• The renal veins return
blood to your heart.
• Blood in these veins
has the right water
and salt concentration
and no urea as all of
these would have
been controlled by the
kidneys.
Simple Overview
• Wastes are filtered
from blood into the
kidneys and sent to
the bladder by the
ureters.
• The bladder has a
urinary sphincter
which acts as a valve
and causes urine to
stay put.
Bladder Trouble???
• When the bladder has 200ml of urine
accumulated it expands and stretch receptors
send a signal to the brain that it is time to go
urinate.
• At 400ml the messages become more frequent.
• At 600ml voluntary control is lost and the urinary
sphincter opens, urine passes out of the body
through the urethra and the bladder is voided.
Kidney Parts
• Kidneys have an outer layer of connective tissue
called the cortex, which encircles the kidney and
where the filtration of blood occurs.
Kidney Parts
• Kidneys have an inner layer under the cortex called
the medulla where the salt and water content of urine
are controlled.
Kidney Parts
• Under the medulla is the hollow chamber called the
renal pelvis which connects the kidney with the
ureter. This is where urine collects.
The Nephron
• The kidney has
around one million
small functional units
inside of it called
nephrons.
Afferent Arterioles
• The afferent arterioles supply blood to the
nephrons from the renal artery.
Glomerulus
• The afferent arterioles end in a high pressure
capillary bed called the glomerulus, which is the
site of filtration.
Efferent Arterioles
• The glomerulus is not
like a normal capillary
bed as it does not
transfer blood to a
venule; instead blood
exits the glomerulus
into the efferent
arterioles.
• This ‘cleaner’,
oxygenated blood will
continue around the
body.
Peritubular Capillaries
• The efferent arterioles lead to a network of
peritubular capillaries (true capillaries) which
surround the tubules of the nephron.
• They are important in urine formation as they can
give to or take ions away from the nephron.
Bowman’s Capsule
• The glomerulus is
surrounded by the
Bowman’s capsule.
• Most of the fluid in the
blood stream that
reaches the glomerulus
will pass into the
Bowman’s capsule.
• It, along with the afferent
and efferent arterioles
and the glomerulus are
in the cortex of the
kidney.
Proximal Tubule
• The Bowman’s capsule leads to a thin tubule called
the proximal tubule. This is where glucose is
reabsorbed back into the bloodstream, so it is not
lost in the urine.
Loop of Henle
• Urine goes from the
proximal tubule around
the Loop of Henle, which
descends into the
medulla of the kidney.
• The medulla cells around
the Loop of Henle spend
all their time pumping
sodium ions out of the
Loop of Henle in order to
create a hypertonic
medulla.
Loop of Henle
• This creates a water
gradient and water
leaves the Loop of
Henle, where it is in
high concentration
and re-enters the
bloodstream, where it
is in low
concentration.
• Hence, the Loop of
Henle is where water
is reabsorbed.
Distal Tubule
• Urine (or filtrate) then moves through the distal tubule.
This is an area where lots of salts (cations) are
reabsorbed.
Collecting Ducts
• Then urine is moved
to the collecting
ducts, which collect
urine from many
nephrons and lead
into the renal pelvis of
the kidney and out
through the ureters to
the bladder.
Homework
p. 348 #1,
3, 5