1. Maintaining an Internal Balance

2. Homeostasis
body systems are constantly adjusting to changes in the external environment to maintain a constant internal environment or homeostasis

3. Optimal Human Body temperature: 37ºC blood glucose level: 0.1%
blood pH: 7.35
hormone levels, blood pressure & flow, etc.
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4. Image from: http://msalvarez1. edublogs
Many body systems interact to maintain homeostasis:
-nervous system: receives sensory information from environment, and transmits signals
throughout the body to regulate homeostasis
-excretory system: rids body of waste and maintains clean internal environment
-endocrine system: regulates levels of essential hormones
-circulatory system: carries hormones & other chemicals, and distributes heat throughout the
body
-immune system: protects body from and fights infections
-digestive system: liver controls amino acid levels, detoxifies harmful substances, manufactures blood proteins
-integumentary system: important for maintaining constant body temperature

5. Homeostatic Mechanisms
sensor
integrator
effector
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6. Negative Feedback
sensors signal integrator (coordinating centre) to counteract any detected changes

7. (Image from: http://www.freewebs.com/sandra02n/)

8. Thermoregulation
the regulation of body temperature by negative feedback mechanisms
very important for homeotherms
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9. Image from: http://schoolworkhelper.net/2010/07/thermoregulation/

10. Ectotherms use external environment to regulate body temperature
include invertebrates, fish, amphibians, reptiles
behavioural & some physiological mechanisms allow ectotherms to remain somewhat homeothermic

11. Endotherms use internal mechanisms to regulate body temperature
e.g., birds, mammals
high energy demands
torpor, hibernation, and estivation are behavioural mechanisms that help endotherms to survive in harsh climates

12. Image from: http://www. nature
Requires a lot of energy to maintain constant internal body T

13. Positive Feedback
signals integrator (coordinating centre) to increase any detected changes
less common than negative feedback
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14. Image from: http://pespmc1.vub.ac.be/feedback.html

15. Positive Feedback
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