Human Excretory System Grade 11

1. E X C R E T O R Y S Y S T E M .
• Life of every organism depends on certain basic processes. Excretion is one among them. Different organisms follow different
modes of excretion. In complex organisms including humans, there is a specialized system for excretion called human excretory
system.
• Excretion is a process in which metabolic waste is eliminated from an organism. In vertebrates this is primarily carried out by the
lungs, kidneys, and skin. This is in contrast with secretion, where the substance may have specific tasks after leaving the cell.
Excretion is an essential process in all forms of life

2. L E S S O N
O B J E C T I V E S .
At the end of the lesson, learners will be able to :
• Explain the purpose of the kidneys, bladder, and urethra.
• Describe the excretory system.
• Demonstrate an understanding of the path of excretory system

3. E X C R E T O R Y I N VA R I O U S O R G A N S
Excretory
organs
include:
The lungs.
The kidney or
bladder.
The liver.
The alimentary
canal (gut) and
The skin.

4. T H E L U N G S
The lungs are part of the respiratory system, but they
are also important organs of excretion. They are
responsible for the excretion of gaseous wastes from the
body. The main waste gas excreted by the lungs is carbon
dioxide, which is a waste product of in cells throughout
the body. Carbon dioxide is diffused from the blood into
the air in the tiny air sacs called in the lungs). By
expelling carbon dioxide from the blood, the lungs help
maintain acid-base . In fact, it is the pH of blood that
controls the rate of breathing. Water vapor is also
picked up from the lungs and other organs of the
respiratory tract as the exhaled air passes over their
moist linings, and the water vapor is excreted along with
the carbon dioxide. Trace levels of some other waste
gases are exhaled, as well.

5. T H E K I D N E Y S &
B L A D D E R .
The paired kidneys are often considered
the main organs of excretion. The
primary function of the kidneys is the
elimination of excess water and wastes
from the bloodstream by the production
of the liquid waste known as . The main
structural and functional units of the
kidneys are tiny structures called
nephrons. filter materials out of the
blood, return to the blood what is
needed, and excrete the rest as urine.
As shown in the Figure , the kidneys
are organs of the urinary system, which
also includes the ureters, bladder, and
urethra — organs that transport, store,
and eliminate urine, respectively.

6. T H E L I V E R .
• The liver (shown in the Figure) has numerous major
functions, including secreting bile for digestion of lipids,
synthesizing many proteins and other compounds, storing
glycogen and other substances, and secreting endocrine
hormones. In addition to all of these functions, the liver is
a very important organ of excretion. The liver breaks
down many substances in the blood, including toxins. For
example, the liver transforms ammonia — a poisonous
by-product of protein catabolism — into urea, which is
filtered from the blood by the kidneys and excreted in
urine. The liver also excretes in its bile the protein
bilirubin, a byproduct of hemoglobin catabolism that forms
when red blood cells die. Bile travels to the small
intestine and is then excreted in feces by the large
intestine.

7. T H E A L I M E N TA R Y
C A N A L ( G U T )
• True metabolic wastes are excreted by
means of the flow of bile from the liver into
the intestine. The destruction of cells in
animals produces bile pigments—residues
of hemoglobin and other pigments—which
may be considered to be the principal
metabolic wastes eliminated via the
alimentary canal

8. T H E S K I N .
The is part of the integumentary
system, but it also plays a role
in excretion through the
production of by sweat glands in
the dermis. Although the main
role of sweat production is to
cool the body and maintain
temperature , sweating also
eliminates excess water and
salts, as well as a small amount
of urea. When sweating is
copious, as in the Figure ,
ingestion of salts and water may
be helpful to maintain

9. T H E U R I N A R Y
S Y S T E M .
• Consist of paired kidneys, renal artery, renal
vein, ureter, bladder and urethra.
• Each kidney is supplied with blood by a renal
artery (impure, oxygenated blood) and drained
by a renal vein (pure, deoxygenated blood).
• Urine exits each kidney through a duct called the
ureter.
• Both urethers drain into a common urinary
bladder, and urine is expelled through a urethra

10. S T R U C T U R E O F K I D N E Y.

11. C O N T I N U AT I O N O F S T R U C T U R E T H E
K I D N E Y.
• Microscopically each kidney is composed of over 1 million tiny tubules called
nephrons.
• The nephrons of the kidneys produce urine.

12. T H E N E P H R O N
• The nephrons of the kidneys produce urine.
• Some nephrons are located primarily in the renal cortex, but others dip down into
the renal medulla.
• The nephron, the functional unit of the vertebrate kidney, consists of a single long
tubule and a ball of capillaries called the glomerulus.

13. N E P H R O N
• https://study.com/learn/lesson/nephron-parts-function-location.html

14. T H E F U N C T I O N O F T H E K I D N E Y I N
U R I N A R Y F O R M AT I O N .
An average person produces between 1 - 2 liters of
urine daily. Urine production requires 3 distinct
processes:
• Glomerular filtration at Malpighian
body (Glomerulus & Capsule of
Bowman.)
• Tubular reabsorption at convoluted
tubules.
• Tubular secretion at convoluted
tubules.

15. U R I N A R Y F O R M AT I O N .

16. G L O M A R U L A R
F I LT R AT I O N .
• Blood enters kidney via renal artery (impure /
oxygenated).
• This branches many times eventually
forming many afferent arterioles, each of
which delivers blood to an individual kidney
nephron.
• The diameter of afferent (incoming) arteriole is
greater than diameter of efferent arteriole (
• Pressure of blood inside glomerulus is increased
due to difference in diameter of incoming & out-going
arterioles.

17. G L O M E R U L A R
F I LT R AT I O N C O N T …
• Increased blood pressure helps to force
following components of blood out of
glomerular capillaries into cavity of
capsule of Bowman:
• Most of the water;
• Most/all of the salts;
• Most/all of the glucose;
• Most/all of the urea.

18. T U B U L A R
R E A B S O R P T I O N
.
 Only about 1% of glomerular filtrate
leaves body (rest - useful substances) is
reabsorbed into the blood .
 Tubular reabsorption & occurs via 3
mechanisms.
They are:
 Osmosis
 Diffusion
 Active
Transport

19. T U B U L A R
R E A B S O R T I O
N C O N T. .
Reabsorption varies
according to body's
needs  enabling
body to retain most
of its nutrients.
Processes of
tubular reabsorption
occur in following
order:
Proximal
convoluted tubule
(PCT).
Loop of Henle
Distal convoluted
tubule (DCT

20. T U B U L A R
R E A B S O R P T I O N :
P R O X I M A L
C O N V U L A T E D T U B U L E .
 Most of volume of filtrate solution is
reabsorbed in proximal convoluted tubule.
 This includes some water and most/all of
glucose.
 Solutes are selectively moved from
glomerular filtrate to BLOOD plasma by
active transport.
 Rest of the glucose, amino acids, & high
amounts of ions, are reabsorbed again
later.

21. T U B U L A R
R E A B S O R P T I O N :
L O O P O F H E N L E .
• Water, urea, & salts contained within ascending
limb of Henle eventually pass into distal
convoluted tubule (DCT).
• DCT reacts to amount of anti-diuretic hormone
(ADH) in blood:
• The more ADH is present in blood, the more water
is re-absorbed into it.
• Because presence of ADH in blood causes cells of
DCT to become more permeable to water,
therefore they allow more water to pass from
tubular fluid back into blood. This results in more
concentrated urine.

22. Tubular
reabsorption IN
the loop of
henle.
If level of ADH in blood is
reduced then cells in DCT
becomes less permeable to
water
• less water is
able to pass
from tubular
fluid back into
blood - which
results in less
concentrated
urine.

23. T U B U L A R
S E C R E T I O N .
• Involves substances being added to tubular fluid.
• Removes excessive quantities of certain dissolved substances
from body.
• Maintains blood at a normal healthy pH (pH 7.35 to pH 7.45)
• Substances that are secreted into tubular fluid (for removal from body)
include:
• Potassium ions (K+),
• Hydrogen ions (H+),
• Ammonium ions (NH4
+),
• creatinine,
• urea,
• some hormones, and
• some drugs (e.g. penicillin).

24. K I D N E Y A N D H O M E O S TA S I S
• Homeostasis  the property of a system in which variables are regulated so that
internal conditions remain stable.
• The kidneys are organs of homeostasis for 4 main reasons:
• Excrete metabolic waste such as urea (primary metabolic waste of humans).
• Maintain the water salt balance in the body.
• Maintain the acid-base (pH) balance in the body.
• Secrete hormones.

25. K I D N E Y A N D H E M E O S TA S I S .
• Through hormone ADH,water is kept constant. (Refer to
reabsorption in DCT)
• Salt is reabsorbed through hormone Aldosterone by means of a
Sodium pump mechanism.
• Aldosterone is a hormone that
• increases the reabsorption of sodium (Na) & water &
• release (secretion) of potassium (K) in kidneys.