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UNIT 3: HOMEOSTASIS

Ch 7: Maintaining an Internal Balance - Homeostasis - Feedback Loops - Thermoregulation. UNIT 3: HOMEOSTASIS. 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

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UNIT 3: HOMEOSTASIS

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  1. Ch 7: Maintaining an Internal Balance - Homeostasis - Feedback Loops - Thermoregulation UNIT 3: HOMEOSTASIS

  2. 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. 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.

  4. 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.

  5. http://www.okc.cc.ok.us/biologylabs/Images/Homeostasis%20Images/Feedback_loop.gifhttp://www.okc.cc.ok.us/biologylabs/Images/Homeostasis%20Images/Feedback_loop.gif

  6. 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

  7. 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.

  8. 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.

  9. http://fig.cox.miami.edu/~cmallery/150/physiol/c44x10thermo-reg.jpghttp://fig.cox.miami.edu/~cmallery/150/physiol/c44x10thermo-reg.jpg

  10. 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

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