28.2 & 28.3: HomeostasisKey Concept: Homeostasis is the regulation and maintenance of the internal environment.Key Concept: Body systems interact to maintain homeostasis

• Homeostasis is the regulation and maintenance of a stable internal environment – this includes temperature, fluids, salts, pH, nutrients, and gases.

• Homeostasis is maintained through internal control systems that respond to change.

Control Systems have 4 parts• Sensors, aka receptors, gather information about conditions in &

out of the body.

• Control center, often the brain, receives info from the sensors and compares these values to the ideal values.• If they are out a range, a message is sent through the communication

system.

• Communication system: Communication is controlled by the nervous system and endocrine system which carry messages to all parts of the body and tells them how to respond to changes.

• Target: Any organ, tissue, or cell that changes its level of activity in response to a message.

• http://www.youtube.com/watch?v=XZxuQo3ylII

Control systems work together through feedback• Feedback: Information from sensor that allows a control center

to compare current conditions to a set of ideal values.• Feedback loop: Sensorcontrol centercommunication

systemtargetsensor….

• Negative feedback loops: control system counteracts any change in the body that moves conditions above or below a set point (reversing change to return conditions to their set points)-most functions in the body are regulated this way.• Ex.: Thermostats, holding your breath

• Positive feedback loops: Control center uses information to increase rate of change away from set points.• Ex.: Cut finger increases clotting factors in blood.

Body systems interact to maintain homeostasis• Example: Thermoregulation – the process of maintaining a steady body temperature• Requires closer interaction of the respiratory, circulatory, nervous, and endocrine systems.

Homeostasis can be disrupted for several reasons• Sensors fail to detect changes in internal or external

environment• Wrong messages sent or correct ones fail to reach targets.• Serious injuries overwhelm homeostatic mechanisms.• Viruses or bacteria change body’s internal chemistry.