Transcript UNIT 3: HOMEOSTASIS - Grade 12 Biology

UNIT 3: HOMEOSTASIS
Ch 7: Maintaining an Internal Balance
- Homeostasis
- Feedback Loops
- Thermoregulation
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...
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.
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.
http://www.okc.cc.ok.us/biologylabs/Images/Homeostasis%20Images/Feedba
ck_loop.gif
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
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.
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.
http://fig.cox.miami.edu/~cmallery/150/physiol/c44x10thermo-reg.jpg
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