Download Excretory System

The Excretory System
The excretory system is the name
given to the skin, lungs and kidneys
which release metabolic wastes to
the outside of the body.
The kidneys, skin and the lungs are the
principle organs of excretion in the
human body. These organs remove the
harmful wastes of cellular respiration CO2 and metabolism of amino acids by
the liver - Urea.
The skin moves wastes out of the body by
dissolving them in the sweat it pours out on
to our skin. It is the wastes within the sweat
that will make you smell.
•The kidneys remove wastes and excess
salts by filtering the blood. They produce a
watery substance called urine.
•Within the urine can be found: urea, salts,
blood cells, hormones, minerals.
•Kidneys control the amount of water
leaving the body, in doing so they regulate
your water homeostasis.
Kidney Structure (Figs. 39-8 & 39-9)
The kidney contains millions of nephrons.
These structures that remove waste while
resorbing useful molecules.
This
Blood
fluid
travels
with
Blood
wastes
fromvessels
renal
travelsare
The
fluid
ininto
artery,
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to
decends
to
the
with
Bowman's
capillaries,
the
tubules
and
The
distal
tubule
loop
of
Henle
and
capsule
then
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and
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and
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into
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valuable
proximal
filtration.
water
tubule.
The
and
this
sends
with
the
distal
(osmosis)
pressure
and
forces
urine
to the renal
tubule.
food
the
molecules
fluid
portion
pelvis.
(active
of thetransport).
blood out.
Water, ions and small molecules filter
from the blood into the Bowman's
capsule. 180 l filtered/day, with only 1
litre excreted as urine (resorbtion).
Cells in the tubules and collecting ducts
pump ions to the blood capillaries by
active transport, water follows as a result
of osmosis. This ensures 99% of H2O and
salts are recovered and that wastes like
urea remain in the tubules for excretion.
Urine travels
from the renal
pelvis in the
kidney out to
the bladder via
the ureters.
Urine is
released
through the
urethra.
Homeostasis of Body Fluids
The kidneys enable the tissue fluid of the
body to remain at a constant concentration.
We lose 1 L from lungs/day, 100mL via
feces, 1 L via kidneys, up to 10 000 mL
through the skin. This water loss can cause
serious problems for our body. Our kidneys
must regain this H2O but too much water is
not good either.
What our kidneys control
•by increasing the permeability of the
collecting duct to water (retain water).
• if you drink too much, the distil tubule
will become impermeable to water
(release H2O)
•Pumping of ions can have an influence
on the concentration of salt in the urine,
which in turn is important for blood
buffers and blood pH.