1. SBI 4U: Metablic Processes
UNIT 3: HOMEOSTASIS
Ch 7: Maintaining an Internal Balance
- Homeostasis
- Feedback Loops
- Thermoregulation
Section 1.3

2. SBI 4U: Metablic Processes
HOMEOSTASIS
Although the world around varies over time, our bodies maintain a stable internal environment
37 degrees Celsius, 0.1% blood glucose, blood pH of 7.35
Homeostasis: the maintenance of a steady-state internal environment despite a constantly changing external environment.
Homeostasis is called a dynamic equilibrium as it allows all body systems to work within an acceptable range.
Dynamic equilibrium is a condition that remains stable within fluctuating limits.
Blood pressure, blood pH, and blood glucose levels and body temperature...all work within a small acceptable range.
To do this the body needs monitoring and feedback systems,
Kidneys – monitor water levels
Pancreas – regulates blood sugar levels
Hypothalamus – regulates body temperature and osmotic pressure...
Section 1.3

3. SBI 4U: Metablic Processes
3 important components to these systems:
A monitor which notices changes in the normal state and sends messages to the
Coordinating Centre which recognizes an organ is working outside its normal limits and sends a message to a
Regulator which returns the body to its normal state.
Example: When exercising CO2 levels in the blood increase due to an increase in cellular respiration.
Sensors in the blood vessels notice this and pass the information to the brain.
The brain analyzes the information, sends a message to the muscles around the chest cavity.
The muscles allow for deeper and more frequent inhalation/exhalation. This gets rid of the CO2 returning levels in the blood back to normal.
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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.
Example: Room temperature falls below 20 degrees Celsius
the thermometer sends a message to the thermostat to turn on the furnace.
Once the room reaches 20 again, the thermostat turns the furnace off.
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.
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5. SBI 4U: Metablic Processes
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6. 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.
Example: before and after pregnancy/labour.
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
Section 1.3

7. SBI 4U: Metablic Processes
THERMOREGULATION
The maintenance 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.
This limitation is overcome by different behaviours or evolutionary adaptations: reptiles sun themselves, tuna's circulatory system keeps their internal organs at a higher temperature than the surrounding water.
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.
Section 1.3

8. SBI 4U: Metablic Processes
The hypothalamus is the region of the brain responsible for maintaining a constant internal temperature.
Important to note that the core temperature of the body is usually different from the peripheral temperature at the extremities.
How we respond to temperature change (Figure 2, p 339).
Too hot:
Sensors in the brain tell the hypothalamus it is too hot
Sends a nerve impulse to
the sweat glands to start sweating and to
the skin blood vessels to dilate to increase the amount of blood reaching the skin as the skin can give off the excess heat
Both these changes cause body temperature to lower back to normal levels.
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9. SBI 4U: Metablic Processes
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10. SBI 4U: Metablic Processes
Too cold:
Thermoreceptors in the skin tell the hypothalamus it is too cold
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 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.
Homework: p341 #1,2,3,5,7,8,10
Section 1.3