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.