The Excretory System in the Human
Objectives
Explain the role of the excretory system in homeostasis
the ability and necessity to maintain constancy of body
temperature, fluid balance and chemistry.
State the function, location, products of the
skin/lungs/urinary system.
Refer to the different methods of temperature regulation
in animals -- Ectotherms and Endotherms
Explain temperature regulation in
humans.
Outline the basic macrostructure & function for the
urinary excretory system - Kidney/Ureters/Urinary
Bladder/Urethra
Explain the role of Kidney in regulating body fluids.
Describe the processes of filtration , reabsorption
and excretion in the medulla & renal pelvis.
Describe pathway of urine from kidney to urethra
Excretion is the removal of metabolic waste
from the body
Metabolism is the sum of all the chemical
reactions in an organism
Excretion is one of the 7 characteristics of living
things (MRS NERG)
Plants do not have the same need for excretion as
animals. Some of their wastes are stored in
vacuoles. Some stored waste is lost when plants
lose their leaves, bark, seeds etc.
Stomata & Lenticels
Plants lose water and oxygen.
Water and oxygen are lost
through the stomata on the
under surface of leaves
during the day and the
lenticels on stems.
At night plants lose carbon
dioxide through their stomata
and lenticels
Homeostasis
Homeostasis is the maintenance of a constant
internal environment in an organism.
Homeostasis means that humans maintain a
constant temperature (37C), fluid balance etc.
Temperature regulation in animals
It is important to maintain a constant temperature
because temperature regulates enzyme controlled
reactions in the body.
Animals use 2 methods to control their
temperature:
1. Ectotherms: Gain or lose heat from or to
their external environment (cold blooded
animals) e.g. fish and frogs
2. Endotherms: Generate their
own heat from metabolic reactions (warm
blooded animals) e.g. birds and
mammals
Temperature regulation in humans
The skin plays a major role in temperature
regulation in humans
It consists of 2 layers
1. Outer epidermis
2. Inner dermis
Beneath these layers is subcutaneous
tissue which contains adipose tissue
Epidermis
1. Malpighian layer – cells are constantly
dividing by mitosis to produce new
epidermis cells
2. Keratin is a waterproof layer on the
surface of the skin
3. Specialised cells in the malpighian layer
produce a coloured pigment called melanin
which gives colour to skin (freckles and
moles occur where melanin is quite
concentrated)
The SKIN
4. Melanin protects skin against UV light.
Dermis
Consists of connective tissue containing a tissue called
collagen.
It contains a variety of structures e.g. nerve receptors,
sweat glands etc.
Functions of Skin
1. Protection
– The epidermis protects the body and acts as a barrier
against entry of pathogens.
- Dermis – protects internal organs
- Melanin – protects skin from harmful UV light
2. Vitamin production
Vitamin D is produced in the skin in following
exposure to UV light. Vitamin D helps intestine
absorb light.
3. Food Store
Fat is stored in the adipose tissue
4. Sense Organ
Skin has a variety of receptors e.g touch and
hot/cold receptors
5. Excretion
Sweat glands in the skin secrete water and salts
form the body.
6. Temperature regulation
a) In cold conditions the skin helps retain heat by
1. Erector muscles contract forming goose
bumps and this causes hairs to stand on end and
trap a layer of warm air that reduces heat loss
from body.
2. Blood vessels contract
(vasoconstriction) and this
reduces heat loss from
the skin.
3. Muscles relax and contract
very rapidly and we shiver
which Produces heat to
raise our body temperature
b. In warm weather we reduce our
temperature by 1. producing sweat
and when this water evaporates it
cools down our skin. (in normal
weather we can lose about 1 litre of
sweat per day). 2. When we get too
hot blood vessels in our skin expand
(dilate) and come near the surface of
the body. This increases heat loss
from the body and cools us down.
Our faces turn red.
Quiz
Controlling body temperature
Body temperature is controlled by the thermo-regulatory centre in the
________. It is kept at 370C as this is the best temperature for
__________ to work in. If the body becomes too hot then blood
vessels _________ and sweat glands release ________. If the body is
too ______ then blood vessels constrict and muscles start to
__________.
Words
–
sweat, enzymes, cold, dilate, shiver, brain
LEARNING CHECK
•
•
•
•
•
•
•
What is an endotherm?
What is an ectotherm?
List the functions of the skin.
What is our normal body temperature?
What happens when we get too hot ?
What happens when we get too cold?
What part of the brain detects changes in
our temperature?
Excretion & Homeostasis
Role of excretory system in homeostasis
1. Regulates body temperature
2. Controlling osmosis
3. Controlling concentration of body fluids.
4. Removing wast products of metabolism
from the body.
Organs of excretion
1. Lungs – excrete water and carbon dioxide
2. Skin – excretes water & salts as sweat
3. Kidneys – Main excretory organ in
humans. They excrete water, salts and urea
in the form of urine.
OUR EXCRETORY SYSTEM
Quiz
• What is excretion?
• What role does excretion play in
homeostasis in the body?
• Name the main waste products of the body.
• Name the main excretory organs of the
body.
The Urinary System
Consists of:
2 kidneys
Two ureters
The Bladder
The Urethra
 The urinary system consists of the kidneys, the bladder and
some ducts (tubes).
Kidneys are:
Fist sized organs located just below the
diaphragm in the small of the back.
Kidney bean shaped with a depression called
the hilium
Blood from the Aorta enters the kidney
through 2 renal arteries
Every minute about 20% of our blood passes
into the kidneys
Cleaned blood leaves the kidneys through the
renal vein into the vena cava
 A section through the kidney shows an outer darker region
(cortex) and a lighter inner zone (medulla).
Cortex
Pelvis
Medulla
Ureter
Quiz
– Identify Cortex, Medulla, Pelvis, Ureter
D
A
B
C
A = Cortex
B = Medulla
C = Ureter
D = Pelvis
KIDNEY LS
 The kidneys work by filtering the blood and then absorbing
back what the body needs to keep. The wastes are allowed
pass to the bladder, for storage and release.
Filtration
Pelvis
Cortex
Reabsorption
Medulla
Ureter
 As urine is produced, it flows into the renal pelvis, then into the
ureter, to the bladder.
1. Filtration—In the outer cortex,
small molecules like glucose,
amino acids, water, urea and
salts filter out of the blood into
narrow tubules.
2. Reabsorption—blood vessels
reabsorb back useful nutrients
from the tubules. Urea, excess
salts and water, are allowed to
continue down the tubule and
on to the bladder.
3. Secretion is the production and release of chemicals
from cells.
Some substances, especially potassium and hydrogen
ions, are secreted from the blood into the tubule in the
cortex region.
When the blood becomes too acidic, hydrogen ions
are secreted into the urine.
By controlling the hydrogen ion concentration in the
blood, the kidneys control blood pH.
The bladder stores the urine, which flows through the
urethra to the outside.
3. Urine is composed of about 96% water, urea, salt, and traces
of other substances such as hormones.
Quiz
– Identify Site(s) of Filtration and Reabsorption
Filtration
Pelvis
Cortex
Reabsorption
Medulla
Ureter
LEARNING CHECK
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•
•
•
What is filtration?
What is reabsorption?
What is secretion?
What is the difference between the kidney
and the bladder?
• What is urine?
Homeostasis – Water Levels in the
Body
 Being a land animal, we have a continuous need to
conserve water.
 Water must be taken in daily and its loss must be carefully
regulated.
 Water is taken in as food and drink, and is also formed
inside the cells during some reactions, especially
respiration.
 Water is lost from the body through our lungs, skin,
intestines and kidneys.
Water is lost from the body through a number of ways:
 Lungs – some water gets evaporated as we exhale from our
warm, damp lungs.
 Skin – by evaporation from cells and through sweat.
 Intestines – in the faeces (undigested food).
 Kidneys – in dissolving the poisons and wastes we wish to
excrete from the body.
 We have no control
over the amount of
water lost each day
from the lungs, skin or
intestines.
 So the kidneys are
the water control
(osmoregulatory)
organs of the body –
conserving or
eliminating water as
the body requires.
LEARNING CHECK
• Name the ways we gain water.
• Name the ways we lose water.
• What is osmoregulation?
Functions of the Kidney
1. Excretion – Kidney removes waste products from the blood
stream and changes them to urine.
2. Osmoregulation – Kidneys control water content of the
body.
3. Salt Concentration – Kidneys control the salt concentration
of body fluids e.g. blood. If we eat too much salt the kidney
will increase the salt content of our urine.
4. pH Control – Kidneys control the pH of body fluids e.g.
blood. Normal pH of blood is 7.4