Post on 08-Feb-2016
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HomeostasisChapter 30 pg 302
Objectives of class
• To define what is meant by the external and internal environment
• To Define homeostasis• To investigate examples of homeostasis in
humans• To discuss how diffusion and exchange works
in homeostasis in humans• To look at methods to improve diffusion and
exchange
External Environment
• The term external environment refers to the surroundings in which an organism lives.
e.g. external environment for Amoeba is fresh water.
Most organisms apart from humans have little ability to control their external environment.
Thermal imaging of humanWhite is hottestRed, orange, green
blue and purple is cooler
Internal Environment
• The internal environment refers to the surroundings of the cells in a multi-cellular organism. E.g. tissue fluid in humans
• All organisms have the ability to control their internal environment to some extent
Homeostasis
• Homeostasis is the ability of an organism to maintain a constant internal environment.
• Homeostasis involves a combination of many processes acting together to control the internal environment.
Examples of homeostasis in humans
Examples of Homeostasis in Humans
• Maintaining body temperature at 370C despite changes in external environment.
• Keeping the pH of the blood and tissue fluids very close to pH7.4
• Preventing the build up of toxic chemicals in the body.
• Maintaining sufficient levels of oxygen in the body.
• The maintenance of homeostasis in humans involves many organs and organ systems e.g.
1. Body temperature is controlled mainly by the skin.
2. Blood plasma and tissue fluid pH is controlled by the kidneys.
3. The prevention of the build up of toxic waste is controlled by the liver and kidneys.