KEY CONCEPT Biology is the study of all forms of life.

Conditions within the body must remain within a narrow range in order for organisms to stay alive. Homeostasis is the regulation and maintenance of the internal environment of living things. Homeostasis involves keeping the internal environment within set ranges. Example: Body temperature. Cold temperatures can lead to goose bumps. Blood flow to the skin decreases. Tiny muscles contract the pores and the skin around body hairs conserve heat.

Organisms must maintain homeostasis to survive in diverse environments. Predict: What will happen to the skin in hot temperatures? Draw conclusions: Why is it so important to maintain homeostasis within the body?

Control systems help maintain homeostasis. sensors gather data control center receives data, sends messages communication system delivers messages to target organs, tissues targets respond to change pore sweat glands hair follicle muscle goose bump

Homeostasis is usually maintained through negative feedback. Negative feedback systems return a condition to its normal (set) point. Most functions in the body are regulated by negative feed back loops Examples: Respiratory rates, thermoregulation, blood sugar levels, hunger and thirst levels, water levels

Negative feedback loops are necessary for homeostasis. Feedback compares current conditions to set ranges. Negative feedback counteracts change. Negative Feedback Loop O2 / CO2 level returns to normal Holding breath, CO2 levels rise, Control system forces exhale, inhale

Positive feedback increases change. Torn vessel stimulates release of clotting factors platelets fibrin white blood cell red blood cell blood vessel clot Growth hormones stimulate cell division The release of hormones to stimulate labor in humans.

A disruption of homeostasis can be harmful. Homeostasis can be disrupted for several reasons. sensors fail targets do not receive messages injury illness

Short-term disruption usually causes little or no harm. Effects usually last a few days or a few weeks. Example: cold or flu virus Long-term disruptions can cause more damage. Example: Diabetes is a serious long-term disruption of homeostasis. 1 2 3 4 Pancreas cells attacked;insulin declines Blood glucose levels rise, Body burns fat; blood more acidic, Cells impaired; all organs damaged. pancreas fats kidneys

Behaviors and adaptations can help maintain homeostasis. Behavior: If you are cold, put on a jacket. Adaptation – polar bears have hollow hair. Summarize: What is homeostasis and why is it important? Fig 2.3 – The polar bear can maintain homeostasis in very cold climates. Its hollow hair is one adaptation that helps the bear retain its body heat. SEM Magnification: 450X