A very important organ system in the body is called the excretory system.
The excretory system consists of a group of organs that remove unnecessary materials, or wastes from
body fluids. Note that the large intestine, which removes solid wastes, is not considered as part of the
excretory system—it is part of the digestive system.
The three main parts of the excretory system in the body are:
Lungs
The lungs, which remove waste gases like carbon dioxide and excess water vapour
Skin
Lungs
The skin, which releases wastes dissolved in perspiration.
Skin
Lungs
Urinary
System
And the urinary system, which removes wastes in the form of urine.
We’ll start by looking at the lungs. If we have a look (click) at this little section here.
And zoom in on it,
Alveoli
These air sacs surrounded by capillaries are called alveoli.
Alveoli
A waste product from cellular respiration, carbon dioxide or CO2, is dissolved in the blood coming
into the lungs.
Alveoli
This diffuses from the capillaries into the alveoli.
CO2
Alveoli
click
CO2
CO2
Alveoli
And it goes into the tubes called bronchioles
CO
CO22
CO2
CO2
And from the bronchioles….
Alveoli
CO
CO22
Alveoli
Into larger tubes called bronchi, then through the trachea, and finally out of the body.
Alveoli
A small amount of water from the blood also enters the alveoli as water vapour
H2 O
Alveoli
(pause and click)
H2 O
H2 O
Alveoli
And like CO2, moves into the bronchioles
HO
H22O
H2 O
H2 O
And from there…
Alveoli
HO
H22O
Alveoli
Through the bronchi, trachea and out of the body. When the air is very cold, the water vapour we breath out
condenses into tiny droplets, which we see as a fog. This is why people say we can “see our breath” when it
is really cold out.
The Skin
Now, we’ll look at another organ involved in excretion, the skin. The skin has 2 to 5 million sweat
glands distributed all over our body. These enable us to perspire.
The Skin
The main purpose of perspiration, or sweating is to cool the body when it is too hot. When water in
sweat evaporates, (click) it takes heat away from the body.
The Skin
And although sweat is mostly water, it does contain some dissolved substances such as urea and lactate, as
well as some minerals. Urea and lactate are waste products. Minerals include sodium or salt, potassium,
calcium, and others.
The Urinary
System
Most of the excretion in our body take place through the urinary system. Let’s take as look at the
major organs and parts of the urinary system.
aorta
renal
artery
The word “renal” means having to do with kidneys. The renal artery branches off of the large artery called
the aorta and brings blood from the heart into the kidneys. This is the right renal artery, bringing blood to
the right kidney.
aorta
renal
artery
Here is the left renal artery, bringing blood to the left kidney.
renal
artery
renal
artery
right
kidney
Here is the right kidney. Notice kidneys are shaped a bit like a bean.
renal
artery
renal
artery
renal
artery
right
kidney
left
kidney
Here is the left kidney. This drawing has removed the outer surface so we can get a better idea of what it
looks like inside. As we’ll see, the main purpose of the kidneys is to filter the blood and remove waste
products from it.
right
kidney
renal
vein
Inferior vena cava
renal
artery
renal
artery
left
kidney
The renal vein takes blood that leaves the kidneys into a large vein called the inferior vena cava and
back to the heart. This is the right renal vein, which takes blood out of the right kidney.
right
kidney
renal
vein
Inferior vena cava
renal
artery
Here is the left renal vein, which takes blood out of the left kidney.
renal
artery
left
kidney
renal
vein
renal
artery
renal
artery
right
kidney
left
kidney
renal
vein
renal
vein
right
ureter
Ureters are tubes leading from the kidneys down to the bladder. They carry urine. This is the right
ureter.
renal
artery
renal
artery
right
kidney
left
kidney
renal
vein
renal
vein
right
ureter
left
ureter
And here is the left ureter.
renal
artery
renal
artery
right
kidney
left
kidney
renal
vein
renal
vein
right
ureter
left
ureter
bladder
The bladder is a hollow organ with muscular walls. It stores urine that comes from the ureters.
renal
artery
renal
artery
right
kidney
left
kidney
renal
vein
renal
vein
right
ureter
left
ureter
bladder
sphincter
At the bottom of the bladder, there is a valve or sphincter, which can open to let urine out of the
bladder.
renal
artery
renal
artery
right
kidney
left
kidney
renal
vein
renal
vein
right
ureter
left
ureter
bladder
sphincter
urethra
The tube leading out of the bladder is called the urethra. Urine runs through the urethra when the
sphincter shown here and a lower one, called the external sphincter are both open.
We’ll start with the whole urinary system…
And we’ll take a closer look at a kidney. In later biology courses, you will learn names for all the
parts of the kidney and regions within the kidney.
A
Nephron
A part we’ll look at here is very important. It is called a nephron. Nephrons are very tiny. An
average kidney contains up to 1.3 million nephrons.
A
Nephron
Here is a diagram representing a single nephron.
a nephron
We’ll enlarge it a bit.
from renal artery
a nephron
Blood from the renal artery enters here. This is blood that hasn’t been filtered yet.
from renal artery
to renal vein
a nephron
And blood leaves the nephron in this blue vessel and goes into the renal vein. This blood has been
filtered by the nephron.
from renal artery
to renal vein
a nephron
urine goes to ureter
Through this duct, urine leaves the nephron, goes into the center of the kidney and then the ureter.
unfiltered
blood
filtered
blood
a nephron
Unfiltered blood goes through the nephron where it is gradually filtered (pause). The filtered blood
leaves the nephron and goes into the inferior vena cava and back to the heart (wait till dissolved).
unfiltered
blood
filtered
blood
a nephron
We’ll look at this process again. The liquid filtered out of the blood is called the filtrate. As it passes through these
yellow tubules it becomes urine. Urine contains wastes that are filtered from the blood. The process is actually much
more complex than what is shown here. You will learn about this in more detail in later biology courses.
unfiltered
blood
filtered
blood
a nephron
We’ll summarize by saying (click) unfiltered blood enters here, (click) filtered blood leaves here and
(click) urine leaves here.
Urine from the nephrons passes into the center of the kidney,
And it fills this region and makes its way down the ureters (pause and watch) and into the bladder.
As time goes on, the bladder gradually fills with urine.
sphincter
And as more urine enters it, the bladder expands to hold it. After a certain amount of expansion,
nerves are triggered, which go to the (click) sphincter and cause it to open
When this sphincter and a lower one controlled voluntarily are both opened, urine leaves the bladder and it
is emptied. In this way, the urinary system has removed, or excreted many waste products from our body.
Acknowledgements for Images Used
"Urinary system" by Jordi March i Nogué [1] - Own
work. Licensed under CC BY-SA 3.0 via Wikimedia
Commons - http://commons.wikimedia.org/wiki/File:
Urinary_system.svg#/media/File:Urinary_system.svg
Acknowledgements for Images Used
"TranspirationPerspirationCommonsFL" by Minghong.
Licensed under CC BY-SA 3.0 via Wikimedia Commons http://commons.wikimedia.org/wiki/File:Transpiration
PerspirationCommonsFL.jpg#/media/File:Transpiration
PerspirationCommonsFL.jpg
"Lungs diagram simple" by Patrick J. Lynch,
medical illustrator - Patrick J. Lynch, medical
illustrator. Licensed under CC BY 2.5 via
Wikimedia Commons http://commons.wikimedia.org/wiki/File:Lu
ngs_diagram_simple.svg#/media/File:Lungs
_diagram_simple.svg
Acknowledgements for Images Used
"Respiratory system complete en" by LadyofHats The image i did myself as sources i used the books:
Sobotta "atlas der anatomie des menschen" ISBN. 3
541 02828 9 , Churchill livingstone "gray's anatomy"
ISBN. 0 433 01505 8, Interamericana. McGraw-hill
"atlas forografico de anatomia del cuerpo humano"
ISBN. 968 25 1677 3. Also used several online
diagrams like ([1] and [2]) Image renamed from
Image:Respiratory system complete.svg. Licensed
under Public Domain via Wikimedia Commons http://commons.wikimedia.org/wiki/File:Respiratory
_system_complete_en.svg#/media/File:Respiratory_
system_complete_en.svg
Acknowledgements for Images Used
"KidneyStructures PioM" by Piotr Michał
Jaworski; PioM EN DE PL - Own work.
Licensed under CC BY-SA 3.0 via Wikimedia
Commons http://commons.wikimedia.org/wiki/File:Kid
neyStructures_PioM.svg#/media/File:Kidney
Structures_PioM.svg
Acknowledgements for Images Used
"Nephron illustration" by Burton Radons Own work. Licensed under CC0 via
Wikimedia Commons http://commons.wikimedia.org/wiki/File:
Nephron_illustration.svg#/media/File:Ne
phron_illustration.svg