1. SBI 4U: Metablic Processes
UNIT 4: HOMEOSTASIS
Ch 7: Maintaining an Internal Balance
- Homeostasis
- Feedback Loops
- Thermoregulation
Section 1.3

2. SBI 4U: Metablic Processes
HOMEOSTASIS
Homeostasis: the maintenance of a steady internal environment despite a constantly changing external environment.
Homeostasis is a dynamic equilibrium. It allows all body systems to work within an acceptable range.
our bodies maintain a stable internal environment of 37 °C, 0.1% blood glucose, blood pH of all work within a small acceptable range.
Section 1.3

3. Feedback Systems
To carry out homeostasis the body needs monitoring and feedback systems:
Kidneys – monitor water levels, pH levels
Pancreas – regulates blood sugar levels
Hypothalamus – regulates body temperature
...

4. SBI 4U: Metablic Processes
Feedback Loops
The way homeostasis is maintained is by means of feedback loops.
The body uses mainly negative feedback loops, processes in which a mechanism is activated to bring the body back to its normal level, to maintain a steady-state.
Section 1.3

5. 3 important components to these systems:
SBI 4U: Metablic Processes
3 important components to these systems:
Coordinating Centre:
recognizes an organ is
working outside its normal
limits, sends message to…
Effector /
Regulator:
returns the
body to its normal
state
Sensor/Monitor:
notices changes in the
normal state
and sends a signal to…
Section 1.3

6. Example: Room temperature falls below 20 °C:
thermostat
turns on
the furnace
Furnace
heats
up room
thermometer
detects the drop
sends a message to

7. Once the room reaches 20 °C again, the thermostat turns the furnace off:
turns OFF
the furnace
Room
stops
heating up
thermometer
detects the RISE
sends a message to

8. Negative feedback
Negative feedback refers to the fact that a change in a variable triggers the coordinating center to counteract any further changes.
Therefore small changes are kept from becoming large.

9. Ex. When CO2 levels in the blood increase due to an increase in cellular respiration:
Brain analyzes
information and
sends a message
to the chest muscles
Deeper and
more frequent
Inhalation
and exhalation
gets rid of excess CO2
Sensors in
the blood vessels
detect high CO2 and
pass the information
to the brain -

10. Positive feedback systems
SBI 4U: Metablic Processes
Positive feedback systems
less common
designed to accept changes in the body and further promote them, therefore, small changes become amplified.
Allow for the body to accomplish something in a very small amount of time.
Section 1.3

11. Example: Labour
Sudden decrease in progesterone --> contraction in the uterus --> cause oxytocin release --> stronger contractions --> baby moves closer to the uterine opening --> more oxytocin released --> even stronger contractions :( --> baby eventually expelled :) --> contractions stop, which stops oxytocin :) :) :).
Hmwk: p 337 #1,2,4,5,6,9

12. SBI 4U: Metablic Processes
THERMOREGULATION
Homeostasis of body temperature within a range in which the organism functions optimally (optimal range).
Ectotherms: animals which depend on air temperature to maintain their metabolic rate, ie. invertebrates (organisms without backbones; fish, amphibians, reptiles)
Their activity is governed by their environment.
Overcome by different behaviours or evolutionary adaptations.
Section 1.3

13. Endotherms: animals which are able to maintain their body temperature regardless of the environmental conditions (birds and mammals).
If the temperature drops then metabolic rate increases and the organism shivers to create heat.

14. SBI 4U: Metablic Processes
The hypothalamus is the region of the brain responsible for maintaining a constant internal temperature (coordinating centre)
Important to note that the core temperature of the body is usually different from the peripheral temperature at the extremities.
Section 1.3

15. How we respond to temperature change:
SBI 4U: Metablic Processes
How we respond to temperature change:
Section 1.3

16. How we respond to temperature change:
Thermoreceptors in the brain detect if we are too hot and send a message to the hypothalamus
Hypothalamus sends a nerve impulse to
the sweat glands to start sweating (evaporative cooling)
the skin blood vessels to dilate to increase the amount of blood reaching the skin in order to give off the excess heat
Both these changes cause body temperature to lower back to normal levels. ( - feedback)

17. SBI 4U: Metablic Processes
Too cold:
Thermoreceptors in the skin tell the hypothalamus it is too cold
Hypothalamus sends nerve signals to
the skin blood vessels to constrict and reduce the amount of blood flow to the skin thus preventing heat loss,
the skeletal muscles to contract and cause us to shiver to generate heat.
Smooth muscles around body hair contract causing the hair to become erect to conserve heat
Body temperature increases back to normal levels (- feedback).
Section 1.3