By now we know that gaseous waste are
 
thrown out of the body by respiration. But
 
our body also produces some nitrogenous
 
waste which are also thrown out of the
 
body. So the biological processes which
 
are required for the removal of harmful
 
metabolic wastes from our body are known
 
as excretion. So in this lesson we'll
 
study excretion in detail. Different
 
organisms have different ways to excrete
 
out the waste products from their body.
 
Many unicellular organisms like amoeba
 
excrete out the waste by simple diffusion.
 
On the other hand many multicellular
 
organisms like all the animals they have
 
specialized organs for this. For example
 
all the humans have kidneys to excrete
 
the waste from their body. So let's study
 
the process of excretion in human beings.
 
The extretory system in us is located in
 
the abdominal region of our body.
 
It consists of a pair of kidneys ,a pair
 
of ureter, a urinary bladder and
 
urethra. The basic filtration unit in an
 
excretory system are the kidneys. The
 
kidneys removes nitrogenous waste like
 
urea and uric acid from the blood and
 
excrete them out of our body in the form
 
of urine. This urine then passes
 
from the kidneys to the ureters and then
 
to the urinary bladder and urinary
 
bladder the urine can get stored
 
temporarily. From this urinary bladder
 
the urine goes out of the body through
 
the urethra.
 
Let's see how this kidneys function?
 
Kidneys are the bean shaped organs
 
which are present in the abdominal
 
cavity of our body. They are present on
 
either side of the backbone. The outer
 
side of the kidneys is convex while the
 
inner side is concave. From this inner
 
concave side renal artery enters the
 
kidney and
 
renal vein and ureter come out from the
 
kidney.
 
Now this is the detailed diagram of the
 
kidney. Don't get frightened after seeing this.
 
Let's see the simplified version of this
 
and these are the nephrons in the
 
kidneys. There are millions of the nephron
 
each kidney. These nephrons are the basic
 
filtration unit present in the kidneys.
 
Now let's have a look on the structure
 
of nephron. It has a cup like
 
structure called Bowman's capsule.
 
This bowmans capsule has a cluster of
 
capillaries in it. This cluster of
 
capillaries it's called glomerulus.
 
Glomerulus receives the blood supply
 
from renal artery. This blood has all
 
the absorbed food in it. So as this blood
 
passes down the nephron, the kidneys
 
reabsorb amino acids, glucose, salts and
 
excess water from it. The material thus
 
left unabsorbed is called urine. This
 
urine is then collected by the
 
collecting ducts and then passed on to
 
the ureters. From ureter it is
 
passed on to urethra via urinary bladder
 
and thus the urine is excreted out of
 
the body. You'll be fascinated to know that
 
in a healthy adult the initial filtrate
 
In kidneys is about 180 litres, but the
 
amount excluded out is only one litre.
 
Let's summarize quickly the main organs
 
of excretion in our body our kidneys .The
 
main filtration unit in these kidneys
 
are nephrons. These nephrons have three
 
parts bowmans capsule, glomerulus and
 
collecting duct. Glomerulus receives the
 
blood supply from renal artery.
 
This blood is full of absorbed food. This
 
absorb food is reabsorbed in these
 
nephrons and the left over part is
 
called urine. The urine is then
 
collected by the collecting ducts and
 
it's transferred to the ureter. From
 
the ureters the urine is passed out
 
through the urethra via urinary bladder.
 
Now you know how important are these
 
kidneys for our bodies, but have you ever
 
thought what would happen if these
 
kidneys get damaged or in case of kidney
 
failure.
 
Don't worry you're not going to die.
 
The science has made such a progress
 
that if our kidneys completely fail, we
 
have artificial kidneys for us to do the
 
work.
 
The artificial kidneys are the devices
 
that remove nitrogenous waste materials
 
from our body by dialysis. As in this
 
whole process blood is being dialyzed so
 
this process is known as hemodialysis. In
 
this process the blood from the
 
patient's body is taken out to the
 
dialysing filter from there it is being
 
filtered and the filter blood is then
 
passed again to the body of the patient.
 
this dialysing filter has a
 
semi-permeable membrane. It is suspended
 
and dialysing fluid which is isotonic to
 
blood, that is the osmotic pressure of
 
the dialysing fluid is same as the
 
osmotic pressure of the blood.
 
Let's have a look at it when the blood
 
from the patient's body is taken out and
 
it's past the dialysing tube, it gets
 
filtered by the process of osmosis. The
 
waste materials from the blood are
 
removed in the dialysing fluid as it is
 
isotonic to blood and then the filter blood
 
is sent back to the patient's body. So
 
now can you tell me the difference
 
between the functioning of our real
 
kidneys and these artificial kidneys?
 
Yes you got it right these artificial
 
kidneys cannot absorb glucose, amino acid
 
salts and the water present in the blood.
 
Now let's see excretion in plants.
 
Excretion in plants.
 
Yes plants also have these products which
 
are to be excreted
 
out of their body. Now let us see
 
some of the various products present in
 
plants and the methods by which they get
 
rid of them. Some of the waste products in
 
plants are oxygen and excess water.
 
Oxygen is excreted out through stomata,
 
while excess water is excreted out
 
through transpiration. Plants excrete out
 
their other waste products either by
 
storing them in vacuoles or by storing
 
them in leaves that eventually fall off.
 
Moreover as we know that plants have
 
many dead cells. So plant store some of
 
the waste materials in these dead cells
 
which are then removed periodically.
 
Plants also secrete some of the waste
 
products in the soil around them. Some of
 
the waste materials in the plants are
 
even useful like gums, resins, tannins and
 
essential oils etc.
