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Think about…
18.1 The concept of homeostasis
18.2 Regulation of blood glucose level
Recall ‘Think about…’
Summary concept map
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18.1 The concept of homeostasis
Do you know what
homeostasis is?
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18.1
The concept of homeostasis
What is homeostasis?
• ability of the body to maintain a
stable internal environment
- composition of blood and tissue fluid
- body temperature
- blood pressure
• important for body to function properly
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18.1
The concept of homeostasis
What is homeostasis?
For example:
Our body is exposed
to changes in the
external environment,
e.g. air temperature
homeostasis
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18.1
The concept of homeostasis
What is homeostasis?
blood
For example:
The condition of
blood and tissue
fluid is kept
constant for proper
functions of cells
capillary
body cell bathed
in tissue fluid 6
18.1
The concept of homeostasis
Parameters of the internal
environment to be kept stable
What parameters
must be kept
constant in our body?
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18.1
The concept of homeostasis
1 Water content in blood
water content affects water potential
in blood
of tissue fluid
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18.1
The concept of homeostasis
1 Water content in blood
enter the
cells
or
leave the
cells
If water potential of tissue fluid is different
from that of the cells, water will …
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18.1
The concept of homeostasis
1 Water content in blood
If too much water is gained …
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18.1
The concept of homeostasis
1 Water content in blood
If too much water is lost …
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18.1
The concept of homeostasis
1 Water content in blood
If too
much
waterfunction
is lost …
cells
cannot
properly and may even die
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18.1
The concept of homeostasis
1 Water content in blood
• regulated by kidneys (腎)
ureters
kidneys
urinary
bladder
urethra
mammalian urinary system
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18.1
The concept of homeostasis
2 Glucose level in blood
• for respiration in cells
energy + CO2 + water
glucose + O2
- level in blood is kept steady to ensure
a sufficient supply
- as it is water soluble, any change in
level affects water potential of the
tissue fluid
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18.1
The concept of homeostasis
2 Glucose level in blood
In humans,
• normal range is 90–100 mg/cm3
• maintained by
liver
pancreas
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18.1
The concept of homeostasis
3 Gas content in blood
• in respiration
glucose + O2
energy + CO2 + water
content in blood is kept steady
to ensure a sufficient supply
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18.1
The concept of homeostasis
3 Gas content in blood
• in respiration
glucose + O2
energy + CO2 + water
dissolves in blood
too much / too little
affects pH of blood and tissue fluid
affects enzyme activity
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18.1
The concept of homeostasis
3 Gas content in blood
• regulated by
breathing
heartbeat
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18.1
The concept of homeostasis
4 Body temperature
• normal range is 36.5–37C
• kept steady for enzymes to function
properly
• regulated by
skin
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18.1
The concept of homeostasis
4 Body temperature
What are the effects of
failing to regulate body
temperature?
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18.1
The concept of homeostasis
4 Body temperature
C
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>37.5
death
CNS breakdown
fever
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loss of consciousness
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muscle failure
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18.1
The concept of homeostasis
Mechanism of homeostasis
• by negative feedback mechanism
(負反饋機制)
Let me explain
What does
with an example.
that mean?
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18.1
The concept of homeostasis
Negative feedback mechanism
When the room temperature
(RT) is higher than the set
temperature (S) …
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18.1
The concept of homeostasis
Negative feedback mechanism
RT > S
thermostat turns compressor
on, cooling the air back to set
temperature
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18.1
The concept of homeostasis
Negative feedback mechanism
When the room temperature
(RT) is lower than the set
temperature (S) …
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18.1
The concept of homeostasis
Negative feedback mechanism
thermostat turns compressor
off, allowing room temperature
to increase
RT < S
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18.1
The concept of homeostasis
Negative feedback mechanism
Three components:
Receptor Detects changes in the level
of the parameter
Control Processes information from
centre
receptor and coordinates
different organs
nervous system or
endocrine system
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18.1
The concept of homeostasis
Negative feedback mechanism
Three components:
Receptor Detects changes in the level
of the parameter
Control Processes information from
centre
receptor and coordinates
different organs
Effector Produces a response opposite
to the original change
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18.1
The concept of homeostasis
Negative feedback mechanism
When level of parameter is higher than normal,
receptor
normal level of
parameter
control
centre
effector
response to
decrease the level
back to normal
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18.1
The concept of homeostasis
Negative feedback mechanism
response to
increase the level
back to normal
receptor
control
centre
effector
When level of parameter is lower than normal,
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18.1
1
The concept of homeostasis
Homeostasis is the ability of the
body to maintain a stable internal
environment.
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18.1
The concept of homeostasis
2 Homeostasis is important for the
survival of organisms because
it provides a stable internal
environment for cells to function.
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18.1
3
The concept of homeostasis
Importance of regulating
Parameter
the parameter
water
Water
• To keep a stable water
content in
potential
potential in cells so
blood
that they can carry out
metabolic activities
properly
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18.1
3
The concept of homeostasis
Importance of regulating
Parameter
the parameter
Glucose
• To provide sufficient
content in
glucose to cells for
blood
respiration
water
• To keep a stable water
potential
potential in blood
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18.1
3
The concept of homeostasis
Importance of regulating
Parameter
the parameter
Gas content • To provide sufficient
in blood
oxygen
oxygen to cells for
respiration
• To maintain a stable pH
for enzymes to work
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18.1
3
The concept of homeostasis
Importance of regulating
Parameter
the parameter
Body
• To maintain a stable
temperature temperature that is
optimal for enzymes
to work
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18.1
The concept of homeostasis
4 The nervous system and the
endocrine system coordinate
different organs to achieve
homeostasis.
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18.1
5
The concept of homeostasis
Negative feedback mechanism
results in responses that have
opposite effects to the changes in
the parameter, so that the level of
the parameter can be restored to
normal.
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18.2 Regulation of
blood glucose level
How do the liver and
pancreas regulate our
blood glucose level?
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18.2
Regulation of blood glucose level
Roles of liver and pancreas
• they work together
• pancreas secretes hormones
insulin
glucagon
both act on liver but with
opposite effects
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18.2
Regulation of blood glucose level
Roles of liver and pancreas
Insulin decreases blood glucose level
excess
glucose
liver cells
glycogen
stored in
muscles
liver
Body cells take in more glucose
body cells
glucose
CO2 + water
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18.2
Regulation of blood glucose level
Roles of liver and pancreas
Glucagon increases blood glucose level
liver cells
stored
glycogen
glucose
Let’s see how blood
glucose level is
regulated by negative
feedback mechanism.
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18.2
Regulation of blood glucose level
Roles of liver and pancreas
higher
than
normal
pancreas secretes
more insulin and
less glucagon
liver cells
and body
cells
normal blood
glucose level
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18.2
Regulation of blood glucose level
Roles of liver and pancreas
higher
than
normal
pancreas secretes
more insulin and
less glucagon
liver cells
and body
cells
Decrease level by:
1 converting more glucose to
glycogen in liver cells
2 increasing glucose uptake and
oxidation by body cells
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18.2
Regulation of blood glucose level
Roles of liver and pancreas
Increase level by:
converting stored glycogen
to glucose
lower
than
normal
pancreas secretes
more glucagon
and less insulin
liver cells
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18.2
Regulation of blood glucose level
Failing to regulate blood
glucose level
What will happen if blood
glucose level is too high?
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18.2
Regulation of blood glucose level
Failing to regulate blood
glucose level
blood glucose level too high
water leaves cells by osmosis
normal metabolism affected
glucose passes out in urine
diabetes mellitus
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18.2
Regulation of blood glucose level
Failing to regulate blood
glucose level
it results when the pancreas
fails to produce or does not
produce enough insulin
diabetes mellitus
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18.2
Regulation of blood glucose level
blood glucose level (mg/100cm3)
200
healthy person
150
level returns to normal
within a short time
100
normal
1
2
glucose intake
3
time (hrs)
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18.2
Regulation of blood glucose level
blood glucose level (mg/100cm3)
200
diabetic
150
level remains high and
then drops very slowly
100
normal
1
2
glucose intake
3
time (hrs)
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18.2
Regulation of blood glucose level
blood glucose level (mg/100cm3)
200
diabetic
150
the drop is due to the loss
of glucose in urine
100
normal
1
2
glucose intake
3
time (hrs)
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18.2
Regulation of blood glucose level
diabetic
glucose level in urine
1
glucose intake
2
time
3 (hrs)
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18.2
Regulation of blood glucose level
Diabetics need
insulin injections
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18.2
Regulation of blood glucose level
blood glucose level (mg/100cm3)
injection of insulin
200
150
diabetic
level drops quickly
100
normal
1
2
glucose intake
3
time (hrs)
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18.2
Regulation of blood glucose level
Failing to regulate blood
glucose level
How about if the blood
glucose level is too low?
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18.2
Regulation of blood glucose level
Failing to regulate blood
glucose level
blood glucose level too low
insufficient supply of glucose
for respiration
neurones cannot function
person becomes unconscious
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Pancreatic hormones
Pancreatic hormones regulate blood glucose
levels
– The pancreas secretes two hormones
•
Insulin
– Signals cells to use and store
glucose
•
Glucagon
– Signals cells to release stored
glucose into the blood
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http://www.sunyniagara.cc.ny.us/val/pancreas2.jpg
The islets are
composed of three
cell types: alpha
cells, beta cells,
and delta cells.
These cells cannot
be readily
distinguished
without special
stains.
The insulin
producing cells are
called  cells and
make up about 70%
of the islet cells.
The glucagon
producing cells are
called  cells and
make up about 15 20% of the islet
cells.
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http://www.cytochemistry.net/microanatomy/Endocrines/pancreas2.jpg
SECRETORY
ROLE
CELL CHARACTERISTICS
 cells of islets
of Langerhans
Glucagon
15 - 20% of the islet cells;
generally more peripherally
located in the islet; more uniform
in size; cytoplasm appears to be
more densely packed than the 
cells
 cells of islets
of Langerhans
Insulin
70% of the islet cells; generally
more centrally located in the islet
Acinus cells
Digestive
enzymes
Usually oriented in a circular
pattern
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Glucose
balance
Body
cells
Insulin
take up more
glucose
Beta cells
of pancreas stimulated
to release insulin into
the blood
Liver takes
up glucose
and stores it as
glycogen
High blood
Blood glucose level
declines to a set point;
stimulus for insulin
release diminishes
glucose level
Stimulus:
Rising blood glucose
level (e.g., after eating
a carbohydrate-rich
meal)
Homeostasis: Normal blood glucose level
(about 90 mg/100mL)
Blood glucose level
rises to set point;
stimulus for glucagon
release diminishes
Liver
breaks down
glycogen and
releases glucose
to the blood
Stimulus:
Declining blood
glucose level
(e.g., after
skipping a meal)
Alpha
cells of
pancreas stimulated
to release glucagon
into the blood
Glucagon
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– Diabetes can be detected
•
By a test called a glucose tolerance test
Blood glucose (mg/100mL)
400
350
300
Diabetic
250
200
150
Normal
100
50
0
0
1
2
1
2
3
Hours after glucose ingestion
4
5
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Diabetes is a common endocrine disorder
– Diabetes mellitus
• Results from a lack of insulin or a failure of cells to
respond to it
– 2 types of diabetes
• Type I (insulin-dependent)
– Autoimmune disease
– Beta cells destroyed, no insulin made
• Type II
– Body cells fail to respond to insulin
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Diabetes type I and type II
Type I - autoimmune
disorder (destroys
ability to produce
insulin)
Type II - due to aging, lifestyle,
heredity and other lifestyle (diet)
factors decreased
responsiveness by cells of target
organs to insulin
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 Complications
related to
Diabetes
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Insulin Pump
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People with diabetes mellitus (糖尿病)
need to check blood glucose level and
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People with diabetes mellitus (糖尿病)
need to receive insulin injections
several times a day…
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This greatly affects
our daily activities.
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A new device consists
of a glucose sensor
and an insulin pump
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The sensor checks the
blood glucose level
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A suitable amount of
insulin is released
automatically into the
body
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18.2
Regulation of blood glucose level
more insulin and
less glucagon secreted
1 more glucose
high blood is converted to
blood
glucose
glucose
glycogen in liver
level
level falls
2 more glucose is
oxidized by body cells
1
normal blood glucose level
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18.2
1
Regulation of blood glucose level
normal blood glucose level
low blood
glucose stored glycogen
is converted to
level
glucose in liver
more glucagon and
less insulin secreted
blood
glucose
level rises
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18.2
Regulation of blood glucose level
2a If the blood glucose level is too
high, cells lose water by
osmosis and their metabolic
activities will be affected.
Glucose may be lost in urine .
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18.2
Regulation of blood glucose level
2bIf the blood glucose level is too
low, cells cannot obtain enough
energy
energy for metabolism and they
may die.
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1
What is the relationship between
diabetes mellitus and insulin?
When the pancreas fails to secrete
enough insulin, a person will have
diabetes mellitus.
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2
Why do people with diabetes mellitus
need to check their blood glucose levels
and receive insulin injections regularly?
Since the blood glucose level varies
with body activities, it is necessary to
check the level and inject suitable
amounts of insulin regularly.
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3
What other modern advances in
science and technology may help control
or cure diabetes mellitus?
Other than insulin injections, diabetes
mellitus may be controlled or cured by
pancreas transplant.
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Homeostasis
is brought about by
nervous
system
endocrine
system
through
negative feedback
mechanism
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Homeostasis
is the maintenance of a
stable internal environment
parameters include
water content
in blood
body
temperature
glucose level gas content
in blood
in blood
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glucose level in blood
is regulated by
insulin
glucagon
act on
secreted by
pancreas
liver
body cells
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